Bio 171 - Lecture 19: Viruses and Emerging Infectious diseases

Why is it hard to disrupt the process of when HIV is infecting a host cell (?) ?

Because viruses are using host enzymes and host machinery to replicate, it can be hard to disrupt the process since you don't want to disrupt human DNA.

What is the prognosis without treatment for an adult with AIDS? Infant?

Can survive for 10-12 years. Infant who is infected can only survive for a few years.

Give examples of diseases with RELATIVELY low R0 values.

Ebola (2), HIV (4), SARS (4), smallpox (3.5-6), influenza (3-4)

endemic

Endemic diseases persist at relatively stable levels in its host population(s) within a particular geographic area.

If your R0 value is larger, would you have to immunize a smaller or larger proportion of the population size?

Larger

Viruses are

Obligate parasites.

What are common example of vectors?

Often arthropods, including insects such as fleas or ticks.

What is the most prominent location in the world where most adults and children are estimated to live with HIV?

Sub-saharan Africa

What domain of life does HIV belong to?

none

capsid

A capsid is the protein shell of a virus. The capsid encloses the genetic material of the virus. It protects the nucleic acid from digestion by enzymes

What are the 4 strategies for treating HIV infections?

1) block entry/prevent fusion 2) block reverse transcriptase: RNA to DNA 3) block integrase: prevent integration of HIV's DNA into host's DNA 4) block protease: Prevent virus from assembling function proteins

You can't have disease transmission without these 2 things:

1) infected person 2) susceptible person

1. Describe the basic structure of a virus and explain how viral replication occurs

1. Capsid surrounds the DNA/RNA genome 2. Envelope surrounds the capsid and is covered by specialized "attachment" proteins 3. Specialized proteins involved with replications 4. Genomes: contain only 1 form of nucleic acid Viral replication occurs in 4 steps: 1) Virus attaches to receptor on cell surface 2) Virus breaches cell membrane; injects nucleic acid into cell 3) Viral nucleic acid replicates using host cell machinery 4) New viral genome and proteins are packaged into particle and released

vector-borne disease

A disease that is transmitted between hosts via a vector, most commonly an arthropod such as a mosquito or tick. Example: Lyme disease and West Nile Virus

disease

An abnormal condition of an organism caused by a PATHOGEN or PARASITE which interrupts the normal bodily functions that often leads to feeling of pain and weakness, and usually associated with symptoms and signs.

antigen

Any foreign substance, usually a protein, that stimulates the body's immune system.

retrovirus

Any of a group of RNA viruses whose RNA is used as a template inside a host cell for the formation of DNA by means of the enzyme reverse transcriptase. The DNA thus formed is inserted into the host cell's genome.

tick

Any one of numerous species of large parasitic mites which attach themselves to, and suck the blood of, cattle, dogs, and many other animals. When filled with blood they become ovate, much swollen, and usually livid red in colour. Some of the species often attach themselves to the human body. The young are active and have at first but six legs.

reservoir

Any person, animal, plant, soil or substance in which an infectious agent normally lives and multiplies. The reservoir typically harbors the infectious agent without injury to itself and serves as a source from which other individuals can be infected.

reverse transcriptase

Definition: Reverse transcriptase is an RNA-dependent DNA polymerase that uses a single-stranded RNA as a template to synthesize a DNA strand that is complementary in sequence to the RNA. The reverse transcriptase then displaces the RNA template and replicates the DNA strand to produce a double-stranded DNA molecule that can be incorporated into the host genome. In synthesizing DNA from an RNA template, the enzyme reverses the usual flow of genetic information from DNA to RNA. Example: Human Immunodeficiency Virus (HIV) is a particularly important virus that uses reverse transcriptase.

pathogen

Disease causing organisms

zoonosis

Disease that moves between non-human animals and human populations. Ebola virus is a zoonosis (zoonotic disease) that periodically moves from bats into human populations.

emerging infectious disease (EID)

Diseases whose incidence has increased recently and whose incidence is likely to continue to increase in the future; however, there are not set criteria for what counts as "recent" and what increase in prevalence is needed for a disease to be considered "emerging." Diseases that were once common, became much less common, and then increased again (e.g., due to evolution of drug-resistance or reduced rates of vaccination) are generally referred to as RE-emerging infectious diseases. Tuberculosis is an example of a RE-emerging infectious disease, it is caused by Mycobacterium tuberculosis, a bacterial pathogen. Tuberculosis is re-emerging because antibiotic resistant strains of M. tuberculosis have evolved.

Lyme disease

Example of vector-borne virus.

How is HIV transmitted?

Exchange of human body fluids, through: Unprotected sex needle sharing blood transfusion with infected blood from mother to infant during labor or through breastfeeding

viral envelope

For some viruses, the capsid is surrounded by lipid bilayer that contains viral proteins, usually including the proteins that enable the virus to bind to the host cells. This lipid and protein structure is called the virus envelope, and is derived from the host cell membranes

pandemic

Global (or at least very widespread) epidemic.

What is the difference between HIV and AIDS?

HIV = human immunodeficiency virus. It causes AIDS. AIDS = Acquired immunodeficiency syndrome.

8. Explain how evolutionary processes can help us explain why HIV is so hard to treat/cure as well as inform treatment strategies

HIV has high genetic variability (very high mutation rate), which makes it difficult to make a vaccine that would work against all strains. Resistant HIV strands evolve.

6. Describe the structure of HIV's genome, explain how HIV enters its host cell, how it converts its RNA into DNA and inserts its DNA into the host cell's genome, the types of cells it infects and how it attacks the immune system

HIV is a retrovirus with a genome made up of single stranded RNA (ssRNA). It enters the host cell by fusing (FUSION) with the receptor on the host cell surface. It converts its RNA into DNA by REVERSE TRANSCRIPTASE which is an enzyme that allows the virus to convert its RNA to DNA It inserts its DNA into the host cell's genome by integrase, which means that you end up with new copies of host (HIV) RNA after host genome replication, new copies of reverse transcriptase, and new copies of protease (??) HIV infects the immune system directly and destroys helper T cells and microphages, which are cells that stimulate the activated B cells to divide and make more of themselves and can make memory B cells

HIV & AIDS

HIV is the virus that causes AIDS, which has killed millions of humans worldwide.

7. Explain the evolutionary origins of HIV; be able to state the organisms that HIV originated in

HIV originated in chimpanzees, and is dubbed SIV if it is in chimpanzees. SIV spilled over into humans, and now it is called HIV.

herd immunity

Herd immunity is a form of immunity that occurs when the vaccination of a significant portion of a population (or herd) provides a measure of protection for individuals who have not developed immunity. It arises when a high percentage of the population is protected through vaccination against a virus or bacteria, making it difficult for a disease to spread because there are so few susceptible people left to infect.

What is the formula for herd immunity?

If (1 - p) * R0 < 1, disease will not spread. For herd immunity, p = 1 - (1/R0), where p is the fraction of population protected by immunity.

infectious period

Length of time that an infected individual is infectious to other individuals

11. Explain the basic life cycle of the Lyme disease bacterium and give evidence supporting the statement that Lyme disease is a fundamentally ecological problem.

Lyme disease is caused by the bacterium Borrelia. Ticks get infected feeding on small mammals, such as the white-footed mice, and become vectors for the disease. They can then bite humans and infect them. 1) Eggs of tick hatch into 6-legged larvae. 2) Larvae attach to and feed on first host and acquire the Borrelia Burgerforri. 3) Larvae molt into nymphs after leaving hosts. 4) Nymphs attach to another host. Nymphs feed on humans, transmitting the disease. 5) Nymphs molt into adults after leaving second host and attach to another host, such as a deer. These infected adults feed on dogs, and sometimes humans, transmitting the disease. Lyme disease is a fundamentally ecological problem because: 1) Resource levels influence small mammal populations 2) Habitat fragmentation/land use change alter small mammal community competition 3) Predators reduce small mammal populations.

Which of these diseases requires the largest proportion of the population to be immunized in order to avoid disease outbreaks? A. ebola B. smallpox C. Influenza D. chickenpox E. Measles

Measles

9.For measles, understand what has allowed it to reemerge in recent years,its effects on other infectious diseases, and the benefits of vaccination.

Measles is incredibly infectious, and can remain in the air for up to 2 hours. It is RE-emerging in recent years because of reduced vaccination rates. Measles suppresses the immune system, and this measles suppression can last 2-3 years (in children) after the infection occurs, which leaves people who survive measles to be more vulnerable to other diseases for 2.5 years after recovery --> basically, the more measles, the higher mortality rates from other diseases because of this "measles suppression." In terms of the benefits of vaccination, for among 1 million children who are vaccinated and do not develop measles, about 999,966 children would not experience a serious adverse effect, meaning that measles vaccination is extremely important for preventing the disease from spreading.

Where is Lyme disease the most prominent in terms of the U.S.

Midwest

Give examples of diseases with RELATIVELY high R0 values.

Mumps (10), Measles (18), chickenpox (10-12), pertussis/whooping cough (16-18)

What are the 2 types of immunity?

Natural - exposure to pathogen Vaccination - Receiving injections of a weakened pathogen or its antigens

What happens if lyme disease is left untreated?

Paralysis, arthritis, nerve pain, inflammation of the brain and spinal cord, problems with short term memory

R0

R nought. Number of secondary infections that result from a single infected individual entering a population of entirely susceptible individuals.

3. Explain why R0 is important and how it can be used to inform vaccination programs

R0 is the number of secondary infections that result from single infected individuals entering susceptible population (CR X TE X IP) = R0. Magnitude of R0 can tell us about how fast the disease will spread --> can be measure of how quickly an outbreak of a disease can spread if you have 1 individual be infected in a population. In terms of informing vaccination programs, R0 value can understand if new disease gets into a new area and how we can deploy the appropriate amount of resources to combat it. Also, it can help hypothesize the possibility of us controlling the disease and maybe eventually eradicating it.

What type of virus is HIV?

Retrovirus. A retrovirus is a single-stranded positive-sense RNA virus with a DNA intermediate and, as an obligate parasite, targets a host cell.

antibodies

Specialized proteins produced by B cells of human immune system that "tag" the virus or bacteria for destruction by various kinds of white blood cells of the immune system

epidemic

Term used when the number of cases of a disease increases in a short period of time. In other words, it is an outbreak of disease.

Describe the feasibility of people incorporating the HIV treatment strategies into their everyday lives.

The anti-retroviral therapy is NOT a cure. It slows the progression to AIDS. Expensive (15K/person). Several pills/day; timing is important. Resistant HIV strains evolve.

immune system

The immune system is a host defense system comprising many biological structures and processes within an organism that protects against disease.

Describe the infection rates of HIV in all parts of the world.

They are different over all parts of the world.

What season do Ticks benefit from and why are they more prominent during this season?

Ticks benefit from milder winter because of global climate change.

virus

Tiny, acellular particles that infect virtually every type of cell known. All viruses are acellular (not consisting of cells), and so are referred to as particles or infectious agents. VIRUSES REQUIRE a host cell. They cannot perform metabolism or replicate on their own - that is, outside a host cell. They are not considered fully alive, even thought they share some properties with living organisms.The great majority of viruses are obligate parasites, but a few viruses and their hosts are mutualists. Viruses are ubiquitous (found in all habitats), and abundant (vastly outnumber cellular life).

What are B cells?

Type of white blood cell responsible for producing antibodies (?)

4. Explain how vaccination and herd immunity work, and how vaccination campaigns are used to try to eradicate some infectious diseases

Vaccination works by: 1) Viral antigens (any foreign substance, usually a protein, that stimulate the body's immune system), that stimulates the body's immune system 2) Certain immune system cells recognize antigens 3) These cells stimulate other immune system cells to produce antibodies to the virus (antibodies are produced by B cells) 4) Later, if the host is exposed to live virus particles, the particles will be coated with antibodies and destroyed by immune system cells. Herd immunity works by: 1) few vaccinated individuals = disease spreads easily 2) Many vaccinated individuals (herd immunity) = unlikely for infectious person to contact a susceptible person since it is less likely to spread among a population with more individuals who are immune. This results in the CHAIN OF TRANSMISSION between sick and unsick individuals to be broken. Herd Immunity equation: p = 1 - 1/R0 (p is fraction of population protected by immunity

Why haven't most people developed mumps or measles considering the very large R0 value for each disease?

Vaccines cause a dramatic decline in each disease

viral replication

Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. ... Most DNA viruses assemble in the nucleus while most RNA viruses develop solely in cytoplasm.

What is a relatively new strategy for treating HIV infections?

Want to disrupt the capsid of the HIV

What do we want R0 to be so that disease cannot spread?

We want R0 < 1.

What are Helper T-cells in charge of?

What's going on in immune system. They stimulate the activated B cells to divide and make more of themselves, also makes memory B cells.

2. Explain the factors that allow an infectious disease to (re)emerge and the factors that affect the spread of an EID

Why do viruses REemerge? high rates of travel, increases in human population size, increased urbanization, encroachment on wilderness areas, evolution of pathogens, environmental change, reduced vaccination rates, health inequalities The factors that affect the spread of an EID: 1) CONTACT RATE: The frequency of contact between infected and susceptible individuals 2) TRANSMISSION EFFICIENCY: The efficiency with which the disease is transmitted from infected to susceptible individuals 3) INFECTIOUS PERIOD: The infectious period, or length of time that an infected individual is infectious to other individuals.

Are viruses highly diverse in overall morphology and in the nature of their genetic material?

Yes.

5. Compare and contrast zoonotic diseases with vector-borne diseases

Zoonotic diseases: Disease that moves between non-human animals and human populations. Example: Ebola, which moves from bats into human populations. Vector-borne diseases: A disease that is transmitted between hosts via a vector, most commonly an arthropod such as a mosquito or a tick. Example: Lyme disease and West Nile Virus, which are also zoonotic. NOT ALL VECTOR-BORNE DISEASES ARE ZOONOTIC --> example: Ebola

vaccination

a substance used to stimulate the production of antibodies and provide immunity against one or several diseases, prepared from the causative agent of a disease, its products, or a synthetic substitute, treated to act as an antigen without inducing the disease.

10. Explain why Lyme disease helps show that a) not all emerging infectious diseases are viruses, and b) vaccines are not just effective against viruses.

a) Lyme disease is caused by a bacterium, Borrelia. b) There is no vaccine because it was originally approved by the FDA in 1998, but the company voluntarily withdrew the vaccine after 4 years due to pressure from anti-vaccination activists. Vaccine for pets in widespread use. New human vaccines in development but at least 6 years away.

Borrelia

any of several spiral, parasitic bacteria of the genus Borrelia, certain species of which are pathogenic for humans, other mammals, or birds.