MBI 111 Exam 3

For latent TB/primary TB/TB infection:

- 1 antibiotic is taken for several months, or two antibiotics are taken for a somewhat shorter length of time. - Treatment is especially important for people who have other medical conditions that put them at high risk for developing active TB. - Some people with latent TB choose to "roll the dice" regarding reactivation and opt to not receive antibiotic treatment.

Creutzfeld-Jakob Disease (CJD)

- 10 -15% of CJD cases are "familial": Inherited due to a gene mutation - 85 - 90% of CJD cases are "sporadic": No known familial connection - Direct contact with infected brain or cerebral spinal fluid is the suspected mode of transmission for the CJD prion

Prevention of chickenpox:

- 2 doses of either the Varicella (VAR) vaccine or MMRV (measles, mumps, rubella, varicella) vaccine - 12 - 15 months of age - 4 - 6 years of age - VAR vaccine can be given to older kids and adults who have not had chickenpox or do not know whether or not they've had it. - Women who do not know their vaccination status or who are unvaccinated and do not know whether they have had chickenpox should receive the vaccine prior to becoming pregnant. Because the vaccine is a live, attenuated vaccine, it cannot be given to a women who is pregnant.

For active TB/secondary TB/TB disease:

- 4 antibiotic are taken for 2 months, plus two other antibiotics are taken for several more months. - Doctors, hospitals, and clinics report active TB cases to their local health department, and the health department is tasked with tracking active TB cases and identifying their contacts. - It is critical and mandatory that anyone with active TB receive antibiotic treatment and that they stick to the treatment plan for its duration. - Active TB patients that do not stick to their treatment plan present a risk to the uninfected because they have the communicable form of the disease. This is the reason the treatment is mandatory. - Because it is crucial that active TB cases stick to the treatment plan, a technique known as Direct Observed Therapy (DOT) can be employed for patients that are unlikely to comply with the plan on their own. In DOT a healthcare provider delivers the drugs and watches the patient take them.

TB Screening: Blood Test (IGRA)

- A blood sample is drawn by a healthcare provider. - the blood is sent to a lab where it is tested for certain types of immune responses in an assay called Interferon-gamma Release Assay (IGRA).

Antibiotic Resistant Tuberculosis

- A significant current threat to the world's health is antibiotic resistant M. tuberculosis. - Issues that have contributed to antibiotic resistance in M. tuberculosis that go beyond the aspects discussed in the video include: -- The antibiotics for TB often have side effects, so people stop taking them before the end of their treatment plan. -- Compliance with such a long treatment plan is difficult to maintain, so people stop taking the antibiotics. -- In certain less developed countries where TB is common and these antibiotics are in the greatest demand, antibiotic supplies can be inadequate, counterfeit antibiotics may be present, and the overall healthcare infrastructure is poor.

Capsid

- All viruses have a capsid - The capsid is a shell that houses and protects the genetic material (nucleic acid) - Capsids are made of protein -- The individual proteins that are used to build a capsid are called capsomeres -- Capsids of some viruses also contain molecules called spikes that project from the capsid --- Spikes are used for attachment to host cells

Hosts of Influenza Viruses: Birds, Pigs, and Humans

- An unusual feature of Influenza viruses is that some strains found in pigs, birds, and/or humans can infect species outside of their usual host range, in other words, a bird strain and a human strain could infect a pig at the same time (an unlucky pig!) - During these infections, the different viral strains can exchange genetic information, creating a hybrid Influenza strain with new or different genetic material - To understand how this can happen, remember that during the assembly phase of viral replication the many new copies of the viral genetic material that were produced during the synthesis phase are enclosed in capsids to create new virusesIf a cell is infected with two different viral strains, there is no means to correctly sort the viral genetic material during viral assembly, so some genetic material from each strain can be enclosed in a given capsid - Because a hybrid virus contains a mixture of genetic material, the surface molecules (antigens) found on these hybrid viruses can be significantly different from the original viruses (in the illustration of the hybrid virus above, the H molecules (blue) from the duck influenza virus have replaced the H molecules from the human influenza virus) - If a human becomes infected with the hybrid strain, illness can be severe since the human has no existing immunity (or even partial immunity) to the new surface molecules (antigens) of this new viral strain

Viruses and Cancer

- Cancer occurs when cell division gets out-of-control -- Unnecessary, abnormal cells accumulate, disrupting the normal functions of the body's organs - Oncogenes are genes that are involved in cancer development - Certain viral infections can result in out-of-control host cell division - Examples: -- Human papillomaviruses (HPV) & cervical cancer -- Hepatitis B virus & Liver cancer

The skin is highly defensive, so how do microbes penetrate the skin?

- Certain microbes can enter the skin via hair follicles and sweat glands which are open to the outside. - Certain microbes can enter the underlying tissues or the bloodstream via breaks in the skin such as cuts, punctures, surgical incisions, insect bites, burns, etc.

In what other ways can infectious diseases occur in the skin?

- Certain microbes can enter via the respiratory tract, and then cause disease in the skin. - Certain microbes can directly infect the surface of the skin.

Streptococcal Toxic Shock Syndrome

- Certain strains of S. pyogenes produce exotoxins that act as superantigens - Superantigens cause an inappropriate, excessive immune response that can lead to shock and death

TB prevention in "high risk" countries:

- Children are vaccinated with the Bacille Calmette-Guerin (BCG) vaccine. - The BCG vaccine was developed in the early 1900s when TB was a leading cause of death worldwide. - It contains live, attenuated Mycobacterium bovis (a strain that causes TB in cows) bacteria. - The BCG vaccine is most useful for preventing extrapulmonary TB in children. - Effectiveness of BCG vaccine in preventing latent or active pulmonary TB is not completely clear.

Variant CJD (vCJD)

- Consumption of beef contaminated with the vCJD prion is the suspected mode of transmission - This is a rare condition - UK accounts for 98% of cases - vCJD kills patients at a much younger age than traditional CJD

MDR-TB: Multidrug resistant TB

- Definition of MDR-TB: M. tuberculosis bacteria that are resistant to at least the two most commonly used TB antibiotics. - Although these strains can usually be treated effectively with the remaining types of antibiotics, patients tend to be sicker than those with non-drug resistant TB. - Resistance makes treatment more complex, and drug side effects more likely, because the common drugs are eliminated from the treatment plan. - The development of MDR-TB is an international concern.

XDR-TB: Extensively drug resistant TB

- Definition of XDR-TB: MDR-TB bacteria that are resistant to two additional TB antibiotics. - These strains are very hard to effectively treat with the remaining small number of antibiotics. - Patients with XDR-TB often die of their disease. - The development of XDR-TB is of extreme international concern.

"Staph Infection": Prevention

- Difficult disease to prevent because 20 - 40% of people carry S. aureus but have no disease - Hygiene, handwashing can help - Special antiseptic lotions can be used by people prone to repeat Staph infections - Disinfection of surfaces - Will not prevent all infections because S. aureus returns to disinfected facilities as soon as carriers return

Release by Budding

- Enveloped viruses are released from the host cell by budding - Viral capsid pushes against the cytoplasmic (cell) membrane which wraps around it, creating the viral envelope - Spikes have been placed in the cytoplasmic (cell) membrane during assembly - Host cell can sometimes survive budding

Adsorption (Attachment)

- Enveloped viruses: Envelope spikes bind specifically to protein or sugar receptors on the host cytoplasmic (cell) membrane - Naked viruses: Capsid proteins bind specifically to protein or sugar receptors on the host cytoplasmic (cell) membrane

Influenza symptoms:

- FEVER, chills, headache, body aches, fatigue, sore throat, dry cough, stuffy nose - Signs and symptoms of influenza are mostly the consequences of the immune response against the virus - The viral infection and immune responses against it can cause destruction of cells lining upper respiratory tract, trachea, bronchi, and that damage can lead to certain signs and symptoms as well, such as a cough

Treatment of chickenpox:

- Fever reducing medications such as acetaminophen (Tylenol) or ibuprofen (Advil) - Comfort treatments that reduce itching such as oatmeal baths or calamine lotion - immunocompromised patients will be prescribed the antiviral drug, acyclovir, or one of its derivatives

Prevention - Safety for Healthcare Professionals

- Healthcare providers caring for COVID-19 patients are at greater risk for contracting and spreading the virus - A higher level of personal protective equipment (PPE) is necessary for those who risk daily workplace exposure - Appropriate care must be taken when putting on or taking off the PPE which includes -- N95 facemask (filters out 95% of airborne pathogens) -- Eye protection -- Gloves -- Gown

Influenza Naming System

- Hemagglutinin (H) & Neuraminidase (N) are important molecules on the influenza viral surface - Hemagglutinin (H) is shown as tan forks and Neuraminidase (N) is shown as pink diamonds - The naming system for Influenza strains uses numbers to represent the molecular variations seen in H and N:H2N2, H3N2, H5N1, etc - For example, the 2009 "swine" flu was H1N1 and H3N2 has been circulating for the past several years

Influenza Mutations & Effect on Immunity

- Immunity develops in an infected person or a vaccinated person due to immune responses against certain surface proteins (antigens), sometimes referred to as spikes, on the influenza virus - Influenza viruses mutate frequently which can result in changes in the proteins (antigens) on their surfaces to which antibodies bind to neutralize the viruses - Influenza epidemics occur each year because the population as a whole is not immune to the new strains that evolve - This is the reason a new influenza vaccine is formulated each year (see above)

Prevention - Personal Safety

- In the absence of a vaccine against SARS-CoV-2, the best way to avoid becoming ill is to avoid exposure to the virus Avoidance involves: - Washing hands often - Use a hand sanitizer of >60% alcohol when washing is not an option - Maintaining a safe distance from others outside the home >6 feet - Covering the mouth and nose with cloth in public places to avoid spread from yourself to others - Clean and disinfect frequently touched surfaces often

Common misconceptions or points of confusion about influenza:

- Influenza is sometimes confused with the common cold due to some overlapping symptoms - Influenza is a much more serious disease than a cold - The term "flu" or "stomach flu" is sometimes used (inappropriately!) when a person has abdominal pain, vomiting and diarrhea (and no respiratory symptoms), although vomiting and diarrhea are not common symptoms of influenza - Diseases that are characterized by abdominal pain, vomiting and diarrhea are called gastroenteritis

Latent Viral Infections

- Initial cycles of viral multiplication and host cell damage/death - At some point, viral activities are controlled by the immune system but the viruses remain in a latent (inactive) state in the host's body - Some latent viruses remain in the host for years/life - Latent (inactive) viruses may reactivate (resume invasion and multiplication) at later times in the host's life and cause disease - Example: Herpes simplex viruses

Prevention:

- Injected inactivated influenza vaccine (the "flu shot") - Due to viral mutations, a new vaccine must be formulated and produced each year - Tamiflu is sometimes used to prevent influenza in the elderly and immunocompromised, especially if they are living in a group environment like a nursing home and there is an influenza outbreak - Hand washing

Acute Viral Infections

- Most common type of viral infection - Repeated cycles of viral multiplication and host cell damage/death - End when the host immune system eliminates the viruses or the host organism dies - Example: Influenza viruses

Viral Host Range

- Most viruses can infect just one cell type of a specific host organism - Host cells include eukaryotic cells (human, animal, plant, fungal, protist) and bacterial cells - Host range of a particular virus is dictated by presence of -- Host cell receptors needed for viral attachment -- Host cell machinery and molecules needed for viral multiplication

For extrapulmonary TB:

- Multiple antibiotics are taken for 12 months - If the disease is advanced before treatment begins, it is often incurable

Assembly

- New viral genetic material is "packaged" into new capsids - New spikes are placed in the host cytoplasmic (cell) membrane if the virus is enveloped

Treatment of shingles:

- Pain medication - Antiviral drug, acyclovir, or one of its derivatives, to reduce healing time, duration of pain, and shedding of the virus

Pertussis

- Pertussis begins with the catarrhal stage which involves cold-like symptoms - Infected person is not aware he/she has pertussis, but B. pertussis can be transmitted to others - Pertussis progresses to the paroxysmal stage which involves uncontrollable coughing - During the paroxysmal stage "extreme" coughing is the only means of clearing the mucus - Coughing due to pertussis can last as long as 3 months - Gasping for breath between coughs results in the characteristic "whooping" sound of pertussis

Pertussis: Potential Consequences

- Pertussis is a dangerous disease in small children and infants - Infant lose the ability to suck leading to malnutrition and dehydration - Infants have a significant risk of death - The cause of death is usually suffocation - Violent, relentless coughing in people of all ages can cause vomiting, break blood vessels in the eyes, and even cause bleeding in the brain and seizures - Survivors usually experience many secondary respiratory infections during convalescence due to damage in the respiratory tract

Prion Action in the Brain

- Presence of abnormal PrP causes normal PrP to become abnormal and accumulate in brain cells - Exactly how brain cells are damaged by accumulated abnormal PrP is not understood

Prion: Proteinaceous Infectious Particle

- Prions are infectious proteins, they are not cells or viruses - A prion is an abnormal form of an important brain protein (PrP) - The abnormal form of PrP has an incorrect structure and does not function in the appropriate way - Prions do not contain genetic material (DNA or RNA) - Prions cause neurodegenerative (brain) diseases

Prions Cause Transmissible Spongiform Encephalopathies (TSEs)

- Protein tangles & open spaces develop in the brain - Neurological damage occurs, eventually resulting in death

Pulmonary TB:

- Pulmonary TB is a chronic infectious disease affecting the lungs. - The term "TB" or "tuberculosis" used by itself usually refers to pulmonary TB. - The vast majority of TB cases are pulmonary.

Potential Complications Related to Strep Throat

- Scarlet Fever - Streptococcal Toxic Shock Syndrome - Rheumatic Fever - Glomerulonephritis

General Characteristics of Viruses

- Scientists in the late 1880s and 1890s discovered that infections could be caused by entities smaller than bacteria - Since most viruses are extremely small they were not seen until electron microscopes were developed in the 1930s - 1940s - Viruses are infectious particles, they are not cells - Viruses are obligatory intracellular parasites: In order to multiply, viruses must invade and take control of a host cell - Viruses are active only inside host cells - Viruses are inactive outside host cells

Examples of TSEs

- Scrapie in sheep and goats•Chronic wasting disease in deer - BSE (Bovine Spongiform Encephalopathy), "Mad Cow Disease", in cattle - Recognized during the 1980s in the UK - Creutzfeld-Jakob Disease (CJD) in humans - Kuru in humans

What are the symptoms of shingles?

- Shingles causes painful vesicles in a localized region (a patch) of the skin. - Where on the body a patch of shingles vesicles appears depends on which "tree" of nerves the virus used to travel from the spinal cord to the skin. - Shingles is a VERY painful disease because the nerves become inflamed. - This high level of pain is what makes shingles a consequential and dreaded disease.

TSEs

- Signs and symptoms: Altered behavior, premature dementia, memory loss, delirium, impaired senses, uncontrollable muscle contractions - TSEs take years to develop, but progress rapidly once they begin•No treatment exists - Death occurs within 1 year of diagnosis

TB prevention in the US (a "low risk" country):

- Skin or blood screening tests for certain groups of people (such as healthcare workers) to identify potential cases - Mandatory antibiotic treatment of active TB cases - Isolation rooms in hospitals for the care of active TB patients - Antibiotic treatment for close contacts of an active TB case - Antibiotic treatment for latent TB cases - Note: The BCG vaccine is not used in the US because after vaccination with BCG, the TB skin test will often be positive. This leads to unnecessary follow up diagnostic testing and emotional distress. From a public health standpoint, use of BCG vaccine also eliminates use of screening with the skin test as a way to find cases, which is the strategy used in the US to find cases.

Enzymes and Matrix Proteins

- Some viral capsids contain one or more enzymes that are needed to initiate the takeover of a host cells - Some viral capsids have matrix proteins in their capsids that help stabilize the viral structure

Gas Gangrene: Treatment

- Surgical removal of infected tissue - Debridement or amputation - Antibiotics - Sometimes hyperbaric (high oxygen) chambers

Extrapulmonary TB:

- The M. tuberculosis bacteria can sometimes spread and cause disease outside the lungs. - Multiple organs and tissues can be affected as shown in the diagram from researchgate.net: -- Extrapulmonary TB is most likely to occur in young children and the immunosuppressed. -- Extrapulmonary TB has a very high case fatality rate (higher than active pulmonary TB).

What happens during latent TB?

- The M. tuberculosis bacteria remain under immune system control in the lungs as long as the person's immune system is functioning well. - The person has no symptoms (remember, there is no disease yet, so it makes sense that there are no symptoms). - The M. tuberculosis bacteria cannot be transmitted (latent TB is non-communicable) because the bacteria are walled off in tubercles. - An amazing statistic is that approximately 2 billion people around the world have latent TB! - Approximately 5 to 10% of latent TB cases will reactivate, leading to active TB, which is a life-threatening disease.

Virus Characteristics

- The S proteins protrude from the viral surface resembling a crown, or corona - SARS-CoV-2 belongs to the genus β-coronavirus, family Coronaviridae - It is an enveloped virus with an unsegmented single-stranded positive-sense RNA genome - It is comprised of four main structural proteins: -- spike (S) glycoproteins -- envelope (E) glycoproteins -- membrane (M) glycoproteins -- nucleocapsid (N) proteins - The genome also codes for 16 nonstructural proteins that are involved in viral replication, maturation, and release. - Scientists published the genome sequence by January 10, 2020, just one month after it was first reported; it took over a year to sequence the SARS-CoV in 2003.

What does a positive IGRA result mean?

- The immune system of the person has fought M. tuberculosis bacteria at some point. - The person probably has latent TB. - The person is referred for diagnostic testing.

What does a positive skin test result mean?

- The immune system of the person has fought M. tuberculosis bacteria at some point. - The person probably has latent TB. - The person is referred for diagnostic testing.

Interpretation of the result depends on

- The size of the skin reaction (the diameter of the raised, (sometimes) red area) - Whether or not the person has a known TB exposure or not - Whether or not the person is HIV+ - Whether or not the person has certain other medical conditions

What is the Drug Treatment Plan for TB?

- The treatment plan varies with each type/stage of TB and is limited by the fact that there are only a handful of antibiotics that have antibacterial activity against M. tuberculosis. - M. tuberculosis bacteria replicate slowly compared to other bacterial species, therefore, antibiotic treatment has to go on for a very long time to ensure all of the bacteria are eliminated from the body. - Many of the anti-TB antibiotics have side effects which makes it difficult to convince patients to stick with their treatment plan.

What are the tests for TB?

- There are two tests that can screen people for TB: A skin test and a blood test. - A screening test result is not used for diagnosis. Positive screening test results must be followed up with one or more diagnostic tests for TB.

History of Covid

- Three β-coronaviruses have crossed the species barrier since 2000 1.SARS-CoV emerged in the Guangdong province of China in 2002 ultimately infecting 8,098 people and causing 774 deaths across 5 continents 2.Middle-East respiratory syndrome coronavirus (MERS-CoV) emerged in the Arabian peninsula in 2012 and remains a public health concern 3.SARS-CoV-2 was identified in December 2019 - Both SARS-CoV and SARS-CoV-2 likely originated from bats as the reservoir, with small mammals as intermediate hosts between bat and human. - MERS-CoV originated from a camel reservoir with direct transfer to humans. - In addition, four low-pathogenicity coronaviruses are endemic in humans. - As of May 2020, there are no approved treatments or vaccines for any coronavirus species.

"Staph Infection": Treatment

- Topical antiseptic and/or topical or oral antibiotics, often a combination of two or more antibiotics are used - Sometimes the furuncle or carbuncle must be cut open and drained to encourage healing - Antibiotic resistance is a major problem - MRSA: Methicillin-resistant S. aureus - Resistant to penicillin and many of its derivatives (and sometimes other types of antibiotics) - VRSA: Vancomycin-resistant S. aureus - Nearly impossible to treat

Pertussis: Actions of Exotoxins

- Tracheal cytotoxin kills ciliated epithelial cells (ciliary escalator) necessary for keeping the trachea (main airway) clear - Pertussis toxin causes production of excessive amounts of thick, "ropey" mucus in the airways of the respiratory tract - Death of large numbers of ciliated cells greatly reduces the ability to move the large amounts of thick mucus up and out of the airway

Prevention - Vaccines

- Under normal circumstances, vaccine development typically takes >15 years from exploration to clinical use. - In the case of a global pandemic with a novel virus, the development is fast-tracked and often involves eliminating stages of testing in animals. - Within the first 6 months of the COVID-19 pandemic, vaccine testing in humans began, largely due to a head start from previous coronavirus research. - Certain steps cannot be rushed, such as the wait to see whether antibodies against the virus develop in response to the foreign agent being introduced into the body. - The goal is to induce production of antibodies that bind to the virus, effectively blocking entry into the host cell.

Shingles (Zoster)

- Viral agent: Varicella zoster virus (also known as Human herpes virus 3, HHV-3) - Shingles will occur only in people who have had chickenpox! - Shingles occurs when Varicella zoster virus (HHV-3) reactivates in a person who had chickenpox previously:As the immune system fights Varicella zoster virus (HHV-3) during chickenpox, the virus travels along the peripheral nerves from the skin vesicles to the spinal cord where the virus becomes latent - Later on when the immune system becomes weakened (for any number of reasons), the virus can reactivate and travel back along the peripheral nerves from the spinal cord to the skin and shingles vesicles will appear - The location(s) of the shingles vesicles on the body is dependent on which nerves were used by the virus to move from the spinal cord to the skin - Shingles is more common in older adults than in younger adults because of the weakening of the immune system that occurs with aging.

Significance

- When does this happen? Human infections with bird or big influenza viruses usually occur in people, such as farmers, that have contact with live pigs or birds (it usually just affects that person and no outbreak occurs because these new strains usually are not transmissible from human to human) - Why is this important? An influenza outbreak or epidemic can occur if an additional mutation occurs that results in sustained human to human transmission of a pig, bird, or hybrid influenza virus - This is the scenario of the 1918 pandemic (pig or bird strain, there is debate about this) and the 2009 H1N1 epidemic (pig strain) - Fortunately the 2009 strain was not as virulent in humans as the 1918 strain

How do microbes enter the respiratory tract?

- When the host inhales droplets that contain microbes - When the host inhales airborne particles carrying microbes - When the host inhales fine mists (aerosols) of contaminated water - When the host inhales fungal spores - When the host transfers microbes from contaminated fingers or objects into the eyes, mouth or nose

Gas Gangrene: Prevention

- Wound cleansing - Surgical removal (debridement) of dead tissue - Antibiotics - Proper management of diabetes

Influenza Deaths

- influenza-related death is usually caused by a secondary bacterial pneumonia that develops in a patient with influenza, not directly by influenza virus, but sometimes influenza itself is the cause of a patient's death - In most flu seasons, most of the deaths occur in the elderly, but babies, toddlers, and children are also a group at significant risk - Because influenza and pneumonia are so tightly linked, they are listed together as a cause of death -- In the US, influenza & pneumonia are typically #8 on the top-10 leading causes of death -- Influenza is NOT a trivial disease!

Testing - 2 Types

1.Diagnostic tests - to determine if an individual is currently infected Types of diagnostic tests available: -- PCR test - this was the first available test; it amplifies and detects viral genetic material (RNA) if present in a person's secretions collected with a swab - Advantages: accurate if sample is taken approximately 3+ days post-exposure, option of at-home saliva test limits need for healthcare provider wearing PPE - Disadvantages: may not catch early infections, takes several days for results, rapid tests (results in less than an hour) lack accuracy Antigen test - this is a newer test that detects viral proteins (those that act as antigens) vs. genetic material - Advantages: results in a few minutes, good screening tool - Disadvantages: not as accurate as PCR test

Prevention of shingles

2 doses of the Shingrix vaccine for people 50 years old and older - Shingrix is much more effective in preventing shingles than the previous vaccine, Zostavax. - Vaccination against chickenpox also prevents shingles because the only people who can get shingles are those who have had chickenpox.

Testing - 2 Types continued

2.Antibody tests - to determine if an individual has had a past infection - This is a blood test to determine the presence of antibodies that appear 5+ days post-infection - Advantages: over 120 tests on the market, good tool to track spread of disease - Disadvantages: most tests are not FDA approved; quality is an issue - NOTE: Because this is a novel virus/disease, as of May 2020, we do not know if the presence of antibodies in the blood provides long-term protection against future exposure to SARS-CoV-2.

Prevention - Public Safety continued

2.DisinfectionThe EPA has an approved list of disinfectants for removal of the virus from most surfaces, particularly frequently touched surfaces such as doorknobs, light switches, ATM machines, faucets, etc.

Prevention - Public Safety continued 2

3.Ultraviolet radiation - UV radiation in the range of 240 to 280 nm is an effective germicide for removing airborne viruses and those on surfaces. - Inactivation results from destruction of nucleic acids due to the formation of thymine dimers that prevent replication and transcription. - This method has been used effectively in hospitals for many years, now, in the advent of SARS-Cov-2, authorities in other public places such as schools, offices, and mass transit are using the technology as a means of disinfection.

Basic Reproductive Number (R0) cont.

A contagious disease has a high R0 value (for example, measles transmitted via aerosol R0 = 12 − 18), compared to a disease that does not spread easily from person to person (for example, Ebola transmitted directly through body fluids R0 = 2). - The maximum R0 for COVID-19 was calculated (May 2020) in the 5 to 6 range, higher than earlier estimates from China of 2.2 to 2.7. - The R0 is crucial to determine what percentage of the population must be immune in order to halt the disease spread. - With an R0 of 5.7 for example, we know that at least 82% of the population must be immune, thereby preventing its spread through herd immunity. - The goal is to get the Re,the effective reproduction rate in the current (recovered/vaccinated) state of the population, to a value of 1 or less.

Direct damage to the host

Accumulated damage from viral multiplication cycle usually results in death of host cells and sometimes in tissue and organ damage

Attachment to host cells

Adhesion molecules on viral surface

Genetic Material

All viruses have genetic material - Genetic material is sometimes referred to as nucleic acid - Viral genetic material (nucleic acid) varies by viral type: RNA or DNA (never both) -- Some viruses have double-stranded DNA (like cells do) as their genetic material -- Some viruses have single-stranded DNA as their genetic material -- Some viruses have double-stranded RNA as their genetic material -- Some viruses have single-stranded RNA as their genetic material Linear or circular -- Some viruses have linear molecules of nucleic acid -- Some viruses have circular molecules of nucleic acid Single segment or multiple segments -- Some viruses have their genetic material in a single segment/circle -- Some viruses have their genetic material in multiple segments/circles

Prevention - Vaccines continued

As of May 2020, there are over 100 COVID-19 vaccines in development, the front-runners include: - Novavax Inc. has a vaccine in clinical trials in Australia -- Harmless copies of the spike protein are synthesized and extracted from insect cells, then packaged into nanoparticles for delivery via vaccine - Moderna Therapeutics began clinical trials in the United States in March 2020 -- Injects mRNA enclosed in a lipid nanoparticle, rather than a protein product, allowing the host cells to make the viral protein for recognition by the immune system - AstraZeneca/Oxford University clinical trials in the United Kingdom include children and the elderly -- A genetically modified adenovirus that cannot replicate in humans has been engineered to produce the SARS-CoV-2 spike protein

Pertussis (Whooping Cough)

Bacterial agent: Bordatella pertussis - B. pertussis bacteria are transmitted through the air and by droplets when infected people cough - Highly contagious•B. pertussis bacteria attach tightly to cells in the mouth and throat, multiply there and produce two exotoxins

Gas Gangrene

Bacterial agent: Clostridium perfringes - C. perfringes is an obligate anaerobe: These bacteria die in the presence of oxygen - C. perfringes can transform into endospores - Endospores are dormant and are not affected by oxygen - C. perfringes endospores are found in soil, fecal matter, intestines, and sometimes on the skin - If C. perfringes endospores enter a wound, they will germinate into actively growing bacteria IF -- The blood supply to the area of the wound has been interrupted resulting in oxygen-freeconditions and -- The tissue is dead or has started to die - Unlike necrotizing fasciitis, gangrene cannot occur in healthy tissue because the presence of oxygen prevents germination of the endospores into actively growing bacteria - Actively growing C. perfringes bacteria produce exoenzymes and exotoxins that kill additional tissue and promote bacterial spread - To make matters worse, the bacteria produce gasses that cause tissues to swell further cutting off blood flow - This results in even less oxygen delivery, more bacterial growth, and more tissue death - Eventually, exotoxins and bacteria will enter the bloodstream resulting in the patient's death

What causes tuberculosis?

Bacterial agent: Mycobacterium tuberculosis

Acne

Bacterial agent: Propionibacterium acnes - Common member of the normal microbiota - Contributing Factors: Skin types (genetically determined) that are prone to trap skin oil (sebum) and dead cells, excessive keratinization of the skin, and male hormones (promote overproduction of skin oil) - Acne begins when pores are blocked by excessive skin oil and dead cells - Black heads - P. acnes bacteria metabolize the oil (sebum) and produce products that induce inflammation in the pores leading to development of pustules (white heads) and/or papules

Scalded Skin Syndrome

Bacterial agent: Staphylococcus aureus - Certain strains of S. aureus produce exfoliative toxin - Exfoliative toxin can enter the bloodstream from a typical Staph skin lesion and spread throughout the body - Exfoliative toxin causes skin to turn bright red and causes top layers of the epidermis to peel away from the lower layers - Without outer skin layers, a patient becomes susceptible to serious secondary infections

"Staph Infection"

Bacterial agent: Staphylococcus aureus - Furuncle = Infected hair follicle or sweat gland -- S. aureus coagulates blood proteins in order to wall itself off from the immune system -- "Walling off" results in a pustule -- Painful due to inflammation -- Mistaken for a "spider bite" - Called a "sty" if an eyelash follicle is infected - Carbuncle = Invasion of tissue surrounding the furuncle - Staph infections can become life-threatening - Invasion of blood stream (septicemia) can result in organ failure and/or shock - Invasion of lungs can result in hard-to-treat pneumonia - Certain strains of S. aureus produce damaging exotoxins and/or superantigens

Streptococcal Pharyngitis (Strep Throat)

Bacterial agent: Streptococcus pyogenes - 80+ Antigenic types: Immunity to one type does not protect against others

Necrotizing Fasciitis

Bacterial agents: Certain invasive strains of Streptococcus pyogenes - Sometimes invasive strains of Staphylococcus aureus - Bacteria enter healthy tissue via a small abrasion or cut - Bacterial strains that cause NF grow rapidly and produce a number of exoenzymes and exotoxins that severely damage surrounding tissue and promote rapid invasion and spread of the bacteria - 25% case fatality rate

Impetigo

Bacterial agents: Staphylococcus aureus and/or Streptococcus pyogenes - Exotoxins (such as exfoliative toxin) produced by certain strains S. aureus and/or S. pyogenes bacteria cause blistering in the outer layers of the skin - Skin peels away and flaky or crusty scabs form - Can be itchy - Not usually a dangerous disease, but in rare circumstances impetigo caused by S. pyogenes can lead to glomerulonephritis - Immune responses cause permanent damage to the kidneys - Common in young children - Bacteria spread easily via direct contact and fomites

Cellulitis

Bacterial agents: Staphylococcus aureus and/or Streptococcus pyogenes - Rapidly progressing infection of the dermis and underlying tissues - Area becomes red, swollen, warm and very painful - Immunocompromised are at higher risk for cellulitis and further spread to the bloodstream or deeper tissues than are people with normal immune function

Prevention - Public Safety

Before areas can safely open to the public, a disinfection plan must be implemented to prevent spread in areas that typically host high numbers: schools, public transit, aviation, shops, restaurants, churches, etc. 1.Natural methods - Studies have shown that SARS-Cov-2 lasts hours to days (one study suggests a maximum of 7 days on the outer layer of mask) on surfaces, less in the sunlight. - Leaving items untouched for over 24 hours, or outside in direct sun can reduce the risk of transmission via a fomite.

Uncoating

Capsid (and envelope) breaks down and the viral genetic material (DNA or RNA) is released within the host cell

Scarlet Fever (Scarlatina)

Certain strains of S. pyogenes produce erythrogenic toxin - Erythrogenic toxin causes scarlet fever: a red skin rash, high fever, and sometimes "strawberry" tongue

Cystic Acne

Chronic inflammation affects deeper layers of the skin resulting in the pits and scars that characterize cystic acne

1964 - 1965 US Rubella Epidemic

Consequences of CRS during the epidemic: - 11,250 fetal deaths - 2,100 newborn deaths - 11,600 cases of deafness - 3,580 cases of blindness - 1,800 cases of intellectual and developmental disabilities

Pertussis: Prevention

DTaP vaccine - 5 doses - Ages 2, 4, 6 months - 3 doses required for basic immunity in infants - Age 15 - 18 months - Age 4 - 6 years Tdap vaccine - Age 11 - 12 years - At least once in adulthood - Antibiotic treatment of cases will reduce likelihood of transmission of B. pertussis to others - Contacts of pertussis cases can be given antibiotics to prevent infection

Public Health Pandemic Control

Effectively managing a pandemic involves 4 coordinated response measures: 1.Testing the population with speed and accuracy 2.Isolation of infected individuals 3.Contact tracing - identifying those who have been exposed to the virus 4.Quarantine - restricting movement of those who were exposed

Treatment - Convalescent Plasma

Extracting plasma from recovered patients and donating it to sick individuals has been carried out for over 100 years for a variety of diseases including measles, polio, and Ebola. - In March 2020, the FDA allowed treatment using donated plasma for patients suffering from life-threatening COVID-19. - The FDA considers it "promising" but not yet "safe and effective." - While the treatment is still considered experimental, anecdotal reports from patients state their condition improved significantly after the plasma was transfused.

Skin Test vs Blood Test (IGRA)

IGRA has fewer false positive results and only requires one visit to a healthcare provider, but is more expensive than the skin test.

Rheumatic Fever

Immune responses against S. pyogenes are misdirected - Against joint tissue leading to arthritis - Against heart tissue leading to permanent heart valve damage

Glomerulonephritis

Immune responses against S. pyogenes sometimes cause permanent damage to the kidneys

Are there any other effects of Varicella zoster virus (HHV-3)?

It is dangerous for a pregnant woman to become infected with varicella zoster virus (HHV-3) because the virus can cross the placenta and infect the developing fetus: - The virus can cause fetal damage such as missing limbs and cataracts of the eye if acquired by a pregnant woman. - The virus can also cause life-threatening disease in a newborn infant is acquired by a pregnant woman.

What does winter have to do with respiratory infectious diseases?

Many people believe (and people have believed this for many centuries), that cold air causes respiratory infectious diseases, but this is not the case - It is the dryness of winter air that promotes (but does not cause) these diseases - Dry winter air promotes upper respiratory tract infections because - Some pathogens survive for long periods of time when dried out - The defensiveness of the host's mucous membranes is reduced by drying - Mucus dries out and isn't as sticky so is less effective at trapping and immobilizing microbes - Breaks/fissures develop in the epithelial cell layer which makes entry easier for the microbes - For example, it's common for people to get more bloody noses in the winter than in the summer because their nasal mucous membranes are dried out and therefore more fragile

Viral Structures

Most viruses have one of four possible structures based on the capsid structure (helical or icosahedral) and whether or not the capsid is surrounded by an envelope:

Release by Host Cell Rupture

Naked viruses are released from the host cell by causing its rupture - Host cell is always killed by this process

Mechanisms of Pathogenicity

Once inside the host cell, the virus takes over the replicative machinery and multiplies within the cell (stage 1) - Direct damage to the infected cell includes rounding, detachment, degeneration, and syncytium formation - Progeny are released from cells through exocytosis, and infect nearby cells - Immune system triggers inflammatory response (stage 2) - If not blocked by the immune system, virions migrate to the lower respiratory tract where they infect alveoli type II cells (gas exchange units) that are rich in ACE2 proteins. - Extensive exocytosis of virus particles leads to apoptosis and death of alveolar cells - Non-specific immune cells release chemokines that stimulate a targeted attack on the infected cells, crippling normal cell function (stage 3) - In critical cases, a "cytokine storm," an overreaction by the immune system, causes immune cells to attack healthy tissues - As of May 2020, the link between the virus and the occurrence of multisystem inflammatory syndrome in children (MIS-C) has not been elucidated.

More Disease Manifestations

Organs/systems affected in critical care patients - Eyes- conjunctivitis more common in critical patients - Nose - patients lose their sense of smell from viral damage of nerve cells in the nasal passage - Lungs - inflammation and breakdown of alveolar walls restrict oxygen uptake and delivery - Liver - overactive immune system and therapeutic drugs affect liver enzymes - Kidneys - damage is common in severe cases either from direct viral attack or multisystem organ failure - Cardiovascular system - virus directly infects cells that have ACE2 receptors leading to clots, inflammation, and heart attacks - Brain - some patients experience confusion, seizures, inflammation, strokes - Intestines - GI tract is rich in ACE2 receptors; 20% of patients experience diarrhea Multisystem Inflammatory Syndrome in children (MIS-C) with exposure to SARS-CoV-2 First reported in April 2020 in the United Kingdom in children who either tested positive for the virus or had an epidemiological link Symptoms include: - Persistent fever - Hypotension - Rashes - Multiorgan involvement (kidneys, heart, GI, vasculature, neurologic) - Inflammation Symptoms present weeks after (often asymptomatic) exposure to the virus As of May 2020, the risk factors for contracting MIS-C are unknown.

Entry into the Host

Portals of entry include: - Nasal and oral passages of the respiratory tract - Conjunctiva of the eyes passing through nasolacrimal duct - Oral cavity and esophagus - Once transmitted, viral S-proteins bind to host cells via angiotensin-converting enzyme 2 (ACE2) (viral tropism) - The physiological functions of ACE2 include lowering blood pressure, controlling fluid balance, and regulating the inflammatory response - ACE2 proteins are present in many tissues, including lungs, kidneys, heart, arteries, and the gastrointestinal tract - Multicellular tropism accounts for the high rate of infectivity - S-proteins embedded in viral envelope bind to ACE2 on host cells, which triggers either viral endocytosis, or membrane fusion and viral genome entry.

TB Diagnostic Testing

Positive screening test results are followed by diagnostic testing which can include a chest X-ray, microscopic examination of sputum to look for the bacteria, and/or laboratory testing of sputum that can conclusively identify the bacteria.

Rubella: Prevention

Prevention - Women who intend to become pregnant should be tested for antibodies to rubella virus and be vaccinated with MMR if no antibodies are present - Pregnant women cannot be vaccinated since the vaccine contains live, attenuated viruses - Another vaccine success story - Rubella vaccine was licensed in 1969 - Fewer than 10 cases of CRS have occurred per year since 1969 (compared to 25,000 - 30,000 in 1964 - 65)

TB Screening: Tuberculin Skin Test

Purified protein derivative (PPD) from M. tuberculosis bacteria is injected just under the skin by a healthcare provider.

Influenza Treatment:

Rest, fluids, and over-the-counter drugs (OTC) can help reduce symptoms - There are a few antiviral drugs that can be used against influenza viruses - Must be taken by second day of the disease process in order to be effective - The most commonly prescribed antiviral drug for Influenza is Tamiflu -- Amantadine and Relenza are other anti-virals that are sometimes used

Epidemiology

Risk Factors - COVID-19 can affect anyone. - As a new disease, ongoing research is being conducted to determine the risk factors for severe illness or complications. - Certain populations are more at risk: -- Individuals aged 65 and older, especially those in a care facility -- Anyone with an underlying medical condition, such as diabetes, asthma, kidney disease, pulmonary disease, blood disorders, obesity/metabolic syndrome, heart conditions -- Immunocompromised individuals due to AIDS, cancer, blood or organ transplantation, and immune deficiencies for example.

Congenital Rubella Syndrome (CRS)

Rubella virus can cross the placenta from an infected pregnant woman and infect the fetus - 35% of babies born to women who become infected with rubella virus during the first trimester of pregnancy will develop CRS - Potential consequences - Deafness - Blindness - Heart, liver, and/or spleen defects - Intellectual and developmental disabilities - Miscarriage - Fetal death - Newborn deat

Virus Transmission

SARS-CoV-2 can be transmitted from animal to human (direct contact) and human-to-human (droplet). - Human-to-human transmission of the virus is primarily through droplets that may travel up to 6 feet from person-to-person, through coughing, sneezing, or talking. - Studies suggest that the virus can become aerosolized and travel farther, remaining viable for up to 3 hours. - Indirect transmission via a fomite is also a concern since the virus can remain viable on surfaces such as plastic, for up to 3 days - Viral particles have been found in fecal samples and there is accumulating evidence for fecal-oral transmission - Population-dense areas, large public gatherings, and facilities such as prisons, cruise ships, and senior living centers provide ideal conditions for spread of the virus.

Potential Complications Related to the Common Cold

Secondary ear and/or sinus infections - Usually caused by bacteria that thrive on fluid and mucus build up due to colds Lower respiratory infections such as bronchitis - No such thing as a "chest cold"

Indirect negative effects on the host

Signs and symptoms are often caused by host cytokines and other aspects of defensive responses against viruses

What are the potential complications?

Some patients will develop bacterial skin infections due to scratching of the vesicles - Scratching can open the vesicles and move bacteria such as Streptococcus pyogenes or Staphylococcus aureus from the skin surface into those opened areas, resulting in a secondary infection. - The most serious complication is encephalitis (inflammation of the brain) which occurs in approximately 1 per 1000 chickenpox cases (0.1%) - Encephalitis can be life-threatening.1 per 1000 might not seem like a large risk, but keep in mind that before the vaccine was available nearly everyone got chickenpox, so there were large numbers of chickenpox-associated encephalitis cases.

What are the potential complications of shingles?

Some patients will develop chronic pain (pain still occurs after the vesicles heal) due to nerve damage.

Envelope

Some viruses have a membrane that surrounds the capsid - The membrane is referred to as the viral envelope - Envelopes usually contain molecules called spikes that project from the envelope -- Spikes are used for attachment to host cells

Disease Manifestations

Stage 1 - Asymptomatic state - Incubation time - median 4 to 5 days, range 2 to 14 days - Virus is detected by a nasal swab and is shed by the host in droplets - Virus propagates, mild innate immune response initiated Stage 2 - Upper airway and conducting airway response - Robust immune response - Clinical manifestations of disease appear 2 to 14 days post-exposure and include cough, fever, shortness of breath, chills, muscle pain, loss of taste and/or smell, sore throat, nausea, diarrhea. - Up to 80% of COVID-19 cases will be either asymptomatic or will arrest at this stage. Stage 3 - Hypoxia, progression to acute respiratory distress syndrome (ARDS) within 8 to 12 days - Critical care/hospitalization necessary - Approximately 15% of COVID-19 patients require oxygen and 5% ventilation - Manifestations include pneumonia, difficulty breathing, persistent chest pain/pressure, confusion, inability to stay awake, bluish lips or skin. - Oxygen levels fall as lungs become filled with fluid, white blood cells, mucus, and cellular debris. - Cytokine storm leads to dramatic drop in blood pressure, leaky blood vessels, formation of blood clots, organ failure.

Pertussis: Treatment

Supportive care at home - Supportive care in the hospital - Usually needed for infants and small children - Although pertussis is caused by bacteria, antibiotics are not effective as a cure because antibiotics cannot reverse the effects of tracheal cytotoxin and pertussis toxin

Strep Throat

Symptoms: Extremely sore throat, fever, sometimes pus-filled lesions on tonsils and/or nausea

What are the strategies used to prevent TB?

TB prevention strategies differ depending on how common TB is in a given country.

What happens during active TB?

The M. tuberculosis bacteria multiply in the lungs and cause damage and the person develops symptomatic disease. - Symptoms include a persistent cough (cough that lasts 2 or more weeks), bloody sputum, chest pain, night sweats, weight loss, lack of appetite, fever and chills, and extreme fatigue - TB patients can become extremely underweight. - That's one of the reasons that TB was once called consumption. - The person appears to be "consumed" by the disease. - The M. tuberculosis bacteria can be transmitted (active TB is the communicable stage) because the bacteria are no longer walled off in tubercles. - One untreated active case will typically infect 10 to 15 people each year! - Untreated active TB is a killer disease. Approximately 60% of untreated cases will die.

Covid Overview

The World Health Organization (WHO) named the novel coronavirus that causes the disease COVID-19 "severe acute respiratory syndrome coronavirus 2" (SARS-CoV-2) in January 2020. - The disease is named from a contraction of the term coronavirus disease 2019.This disease was first observed in humans in Wuhan, China in December 2019. - The WHO declared COVID-19 a Public Health Emergency of International Concern (PHEIC) on January 30, 2020.

What happens when a person inhales M. tuberculosis bacteria and the bacteria reach the lungs?

The bacteria are immediately destroyed by lung macrophages and no infection occurs (and that is the end of the story!) OR the person develops an infection in which the bacteria replicate in the lung macrophages (rather than being killed by them), spread into the lung tissue, and then are eventually controlled and are "walled off" in structures called tubercles by the immune system's activities. - This controlled M. tuberculosis infection is referred to as latent TB (or primary TB or TB infection).

Viral Multiplication Cycle

The steps in the multiplication cycle of animal and human viruses are - Adsorption (Attachment) - Penetration - Endocytosis or fusion - Uncoating - Synthesis - Assembly - Release from the host cell - Cell rupture or budding

Treatment - Drugs

There are no FDA-approved drugs for COVID-19 as of May 2020. Some therapies have been suggested as being hopeful: - Remdesivir -- The antiviral drug showed promise against SARS and MERS, also coronaviruses; it works by targeting RNA-dependent RNA-polymerase• - Chloroquine/hydroxychloroquine -- There is limited evidence to suggest that these antimalarial drugs effectively treat patients with COVID-19 - Vitamin C -- Some critically ill patients have been given high doses of vitamin C, however there is no convincing evidence that it works

Scalded Skin Syndrome:Treatment & Prevention

Treatment - Antibiotics - Antibiotic resistance is a major problem - Most patients survive if treatment begins quickly Prevention: - Hygiene, handwashing - Usually affects newborns and young children, so hand washing by caregivers is key

Strep Throat: Treatment & Prevention

Treatment - Antibiotics - Presence of S. pyogenes should be confirmed by testing before antibiotics are prescribed - Can prevent serious complications Prevention - Hand washing

Cellulitis: Treatment & Prevention

Treatment - Antibiotics - S. pyogenes is sensitive to most antibiotics - S. aureus often antibiotic resistant, so healthcare providers choose a drug that is likely to kill S. aureus since it will kill S. pyogenes as well - Sometimes surgery is needed to remove (debride) infected, damaged tissue Prevention - None

Measles: Treatment & Prevention

Treatment - Fever reducers - No antiviral drugs exist to cure measles Prevention - Vaccination - 2 doses of MMR (measles, mumps, rubella) or MMRV (measles, mumps, rubella, varicella) vaccine - 12 - 15 months of age - 4 - 6 years of age

Rubella: Treatment & Prevention

Treatment - No antiviral drugs exist to cure rubella or CRS Prevention - Vaccination - 2 doses of MMR (measles, mumps, rubella) or MMRV (measles, mumps, rubella, varicella) vaccine - 12 - 15 months of age - 4 - 6 years of age

Common Colds: Treatment & Prevention

Treatment - Over the counter drugs (OTC) help with symptoms - No antivirals are available Prevention - Hand washing

Infectious Mononucleosis: Treatment & Prevention

Treatment - Rest, fluids, OTC for symptoms - No antivirals are available Prevention - None, due to the large number of carriers shedding EBV at any given time

Necrotizing Fasciitis: Treatment and Prevention

Treatment - Surgery: Debridement and/or amputation to remove infected, damaged tissues - Antibiotics - Early diagnosis is critical Prevention - None

Impetigo: Treatment & Prevention

Treatment - Topical or oral antibiotics - S. pyogenes is sensitive to most antibiotics - S. aureus often antibiotic resistant, so healthcare providers choose a drug that is likely to kill S. aureus since it will kill S. pyogenes as well Prevention - Hygiene, handwashing

Acne: Treatment & Prevention

Treatment: - Drugs that reduce oil production - Isotretinoin - Drugs that target P. acnes - Benzoyl peroxide and antibiotics - Drugs that reduce inflammation - Salicylic acid - Oral contraceptives - And quite a few others

Infectious Mononucleosis

Viral agent (majority of cases): Epstein-Barr Virus, EBV (aka Human herpes virus 4, HHV-4) - EBV infects cells in salivary glands -- B and T cells multiply to abnormally high level (leukocytosis) - Following viral control by immune responses, EBV becomes latent - 90% of world's population has been infected - Latent EBV can reactivate and be transmitted to others - Any infected person can unknowingly shed EBV in their saliva at any given time Symptoms: Fever, sore throat, swollen lymph nodes, severe fatigue, sometimes gray-white patches in throat, skin rash, enlarged spleen and liver - Children usually have no symptoms - Getting infected at ages 15-25 more likely to result in symptoms - 15% of college students get symptomatic mono - Mono is rarely fatal - Risk of death is due to the chance that the spleen will rupture due to a blow to the abdomen

Measles

Viral agent: Measles virus - Extremely contagious - Transmitted by respiratory droplets - Virus enters the body through the respiratory tract - Virus infects cells in the respiratory tract, invades the bloodstream, then infects skin cells and the cells of various organs - Many cells are destroyed - Cell-mediated immune responses are disabled - Increased susceptibility to secondary infections - Symptoms: Red, maculopapular skin rash, sore throat, dry cough, fever, headache, Koplik's spots in mouth - Measles is a serious disease, especially in infants - As many as 1/3 of measles cases require hospitalization - Potential complications of measles: - Encephalitis (Inflammation of the brain) - Occurs in 1/100 cases - Pneumonia - Occurs in 6/100 cases - Secondary bacterial infections - Hundreds of thousands of children die each year of measles in developing countries - Malnourishment + measles virus leads to severe disease

Rubella (German Measles)

Viral agent: Rubella virus - Highly contagious, very mild disease - Transmitted by respiratory droplets - Virus enters the body through the respiratory tract - Symptoms: Rash and low fever - Often so mild that the disease goes undetected in both children and adults

Chickenpox (Varicella)

Viral agent: Varicella zoster virus (also known as Human herpes virus 3, HHV-3) - Varicella zoster virus (HHV-3) is highly contagious. - Varicella zoster virus (HHV-3) is transmitted via respiratory droplets from a person with chickenpox and via fluid from the vesicles of chickenpox or shingles. - Varicella zoster virus (HHV-3) enters a new host through the respiratory tract - Even though chickenpox falls into the category of infectious diseases of the skin because that is where the disease's effects are visible, the portal of entry is the respiratory system! - Chickenpox causes itchy skin vesicles all over the body and a fever. - The disease and its symptoms are typically more severe in teenagers and adults than they are in children.

What causes influenza?

Viral agents: Influenza viruses

Common Colds

Viral agents: Rhinoviruses, Coronaviruses, and others (200+ viruses can cause colds) - Symptoms: Runny nose, sneezing, scratchy throat (usually NO FEVER in older kids, adults) - Getting chilled does not cause colds

Penetration by Fusion

Virus enters host cell as the viral envelope fuses with the host cytoplasmic (cell) membrane

Penetration by Endocytosis

Virus enters the host cell as the host cytoplasmic (cell) membrane surrounds it

Persistent Viral Infections

Viruses actively invade cells and multiply at low levels within the host for months or years causing slowly increasing amounts of cellular/tissue damage - Examples: Hepatitis B and C viruses

Synthesis

Viruses direct the host cell to - Make copies of viral genetic material (DNA or RNA) - Make new capsid proteins - Make new spikes if the virus is enveloped - To maximize production of viral components, some viruses disrupt the normal functions of the host cell by preventing the cell from producing its own proteins and/or conducting its metabolic processes

Evasion of host defenses

Viruses replicate within host cells. Ability to invade and exist within host cells offers partial protection from host defenses

Naked Virus

Viruses that lack an envelope are referred to as naked viruses

Envelope Virus

Viruses with an envelope are referred to as enveloped viruses

What happens during reactivation?

When a person with latent TB becomes immunodeficient for any number of reasons (sometimes the immunodeficiency is caused by something as basic as aging or malnutrition), the M. tuberculosis bacteria can escape immune control, and begin multiplying in the lungs and causing damage. - This condition is referred to as active TB (or secondary TB or TB disease). - The combination of TB and HIV is particularly devastating. - A person who has latent TB and is HIV positive has a much greater chance of reactivation than a patient who has latent TB but is HIV negative because of the immune system destroying activities of HIV.

Basic Reproductive Number (R0)

When dealing with a novel infectious agent like SARS-CoV-2, epidemiologists are anxious to determine the ability of the infectious agent to spread throughout a population. - The capacity to spread can be quantified - it is given an R0 ("R naught") value, which represents the number of individuals that can be infected from one single person. - The R0 is not a constant number, it can vary depending on the environment (for example, population density) and the behavior of the population (for example, social distancing), but assumes that all members are susceptible to the infectious agent. - An R0 of less than 1 suggests a disease will ultimately die out in a population