Human Biology Chapter 8 Section 2: Infectious Diseases and Human Health

Tuberculosis

In 1882, Robert Koch was the first to see the causative agent of tuberculosis (TB) with a microscope. At that time, TB caused around 14% of deaths in Europe. The disease was called consumption, because it seemed to consume the patients from the inside until they wasted away. In the 1940s, with the advent of effective antibiotics to fight TB, it was thought that the disease could be eliminated. However, control measures were not implemented consistently and tuberculosis cases began to rise in the 1980s. It is estimated that one-third of the world's population has been exposed to TB. In 2014, approximately 9.6 million people were infected with TB, and 1.2 million died. HIV infections are a contributing factor to the increase in TB cases. Tuberculosis is currently the number one cause of death in AIDS patients.

Two types of HIV tests

those that look for the immune system's response to the virus (antibody tests), and those that detect the presence of the actual virus (antigen and RNA tests).

Fusion/entry

Viral envelope fuses with host cell, HIV RNA is released

Budding

Virus exits host cell

Approximately what proportion of the world's human population has been exposed to TB?

one-third

Select all correct descriptions of malaria.

-cyclical pattern of symptoms corresponds with bursting of red blood cells -severe anemia is possible -can be diagnosed by viewing parasites in blood

Toxoplasmic encephalitis

A protozoan parasitic infection, often seen in the brains of AIDS patients

HIV life cycle

1.Attachment. 2.Fusion. 3.Entry. 4. Reverse transcription. 5. Integration. 6. Biosynthesis and cleavage. 7.Assembly. 8. Budding.

The incubation period of tuberculosis (from infection to appearance of illness) is relatively long, ranging from

4 to 12 weeks.

Incubation period of tuberculosis

4-12 weeks

Mycobacterium tuberculosis

A bacterial infection usually of lymph nodes or lungs but may be spread to other organs. In nature, it is a very slow-growing bacterium. The cells have a thick, waxy coating and can exist for weeks in a dehydrated state. The organism is spread by airborne droplets introduced into the air when an infected person coughs, sings, or sneezes. The bacteria can float in the air for several hours and still be infectious.

Invasive cervical cancer

A cancer of the cervix, which spreads to nearby tissues

Outbreak

A disease epidemic that is confined to a local area.

Pneumocystis jiroveci pneumonia

A fungal infection of the lungs

Vector

A living organism—usually an insect or animal—that transfers the pathogen from one host to another.

Category A: Acute Phase

A person in category A typically has no apparent symptoms (asymptomatic), is highly infectious, and has a CD4 T-cell count that has never fallen below 500 cells per cubic millimeter (cells) of blood, which is sufficient for the immune system to function normally. A normal CD4 T-cell count is at least 800 cells.

Category B: Chronic phase

A person in category B has a CD4 T-cell count between 499 and 200 cells, and one or more of a variety of symptoms related to an impaired immune system. The symptoms include yeast infections of the mouth or vagina, cervical dysplasia (precancerous abnormal growth), prolonged diarrhea, thick sores on the tongue (hairy leukoplakia), and shingles (to list a few). Swollen lymph nodes, unexplained persistent or recurrent fevers, fatigue, coughs, and diarrhea are often seen as well. During this chronic stage of infection, the number of HIV particles is on the rise. However, the person does not as yet have any of the conditions listed for category C.

Fusion

After attachment occurs, HIV fuses with the plasma membrane and the virus enters the cell.

Pandemics

An increase in the occurrence of a disease within a large and geographically widespread population (often refers to a worldwide epidemic).Global epidemics are called pandemics. HIV/AIDS, tuberculosis, malaria, and influenza are all examples of current pandemics.

Kaposi sarcoma

An unusual cancer of the blood vessels, which gives rise to reddish-purple, coin-sized spots and lesions on the skin.

Tuberculosis is caused by what type of microbe?

Bacterium

Assembly

Capsid proteins, viral enzymes, and RNA can now be assembled to form new viral particles.

Reverse transcriptase

Catalyzes reverse transcription, the conversion of the viral RNA to viral DNA.

Protease

Catalyzes the breakdown of the newly synthesized viral polypeptides into functional viral proteins.

Integrase

Catalyzes the integration of viral DNA into the DNA of the host cell.

Category C: AIDS

Category C: AIDS A person in category C is diagnosed with AIDS. When a person has AIDS, the CD4 T-cell count has fallen below 200 cells/ or the person has developed one or more of the 25 AIDS-defining illnesses (opportunistic infections) described by the CDC's list of conditions in the 1993 AIDS surveillance case definition. Persons with AIDS die from one or more opportunistic diseases rather than from the HIV infection. Recall that an opportunistic illness occurs only when the immune system is weakened. These diseases include the following: Pneumocystis jiroveci, Mycobacterium tuberculosis, Toxoplasmic encephalitis, Kaposi sarcoma, Invasive cervical cancer. Once one or more of these opportunistic infections have occurred, the person will remain in category C. Newly developed drugs can treat opportunistic diseases. Still, most AIDS patients are repeatedly hospitalized due to weight loss, constant fatigue, and multiple infections. If untreated, death usually follows in 2 to 4 years. Although there is still no cure for AIDS, many people with HIV infection are living longer, healthier lives due to the expanding use of antiretroviral therapy.

Biosynthesis

Cell produces viral RNA, and viral proteins

Which of these features is unique to the retroviruses?

Convert viral RNA into DNA

Acquired immunodeficiency syndrome (AIDS)

Disease caused by HIV and transmitted via body fluids; characterized by failure of the immune system. Acquired immunodeficiency syndrome (AIDS) is caused by a virus known as the human immunodeficiency virus (HIV).

Infectious disease

Diseases caused by pathogens such as bacteria, viruses, fungi, parasites, protozoans, and prions. An infectious disease is classified as an epidemic if there are more cases of the disease than expected in a certain area for a certain period of time.

Entry

During a process called uncoating, the capsid and protein coats are removed, releasing RNA and viral proteins into the cytoplasm of the host cell.

Budding

During budding, the virus acquires its envelope from the host cell's plasma membrane.

How often is the HIV/AIDS infection rates and deaths updated?

Every 2-3 years.

True or false: One benefit of highly active antiretroviral therapy (HAART) is that it can eliminate all HIV proviruses.

False

Summarize the HIV replication cycle, and list the types of cells this virus infects.

HIV attaches to the target cell, fuses with the plasma membrane, and enters the cell. Capsid and protein coats are removed, releasing RNA and viral proteins. Viral reverse transcriptase converts viral ssRNA to dsDNA, which is transcribed into RNA, which is integrated into the host cell's DNA. Once activated, this provirus directs the synthesis of viral RNA, some of which directs the synthesis and assembly of more virus particles. These bud from the cell, acquiring an envelope containing markers. HIV infects helper T cells and macrophages that display the molecule CD4.

HIV Structure

HIV consists of two single strands of RNA (its nucleic acid genome); various proteins; and an envelope, which it acquires from its host cell. The virus's genetic material is protected by a series of three protein coats: the nucleocapsid, capsid, and matrix. Within the matrix are the following three very important enzymes: reverse transcriptase, integrase, and protease.

Transmission and prevention of HIV (yikes)

HIV is transmitted by sexual contact with an infected person, including vaginal or rectal intercourse and oral-genital contact. It can also be transmitted through needle sharing among intravenous drug users. A less common mode of transmission (and now rare in countries where blood is screened for HIV) is through transfusions of infected blood or blood-clotting factors. Babies born to HIV-infected women may become infected before or during birth or through breast-feeding after birth. From a global perspective, heterosexual sex is the main mode of HIV transmission. In some nations, however, homosexual men, IV drug abusers, and sex industry (prostitution) workers are the most common transmitters of HIV. Differences in cultures, sexual practices, and belief systems around the world influence the type of HIV prevention strategies needed to fight the spread of the disease.Blood, semen, vaginal fluid, and breast milk are the body fluids known to have the highest concentrations of HIV. HIV is not transmitted through casual contact in the workplace, schools, or social settings. Casual kissing, hugging, or shaking hands doesn't spread the virus. Likewise, you can't be infected by touching toilet seats, doorknobs, dishes, drinking glasses, food, or pets. The general message of HIV prevention across the globe is abstinence, sex with only one uninfected partner, or consistent use of a condom during sexual encounters.

Stages of an HIV infection

In category A individuals, the number of HIV particles in plasma rises on infection and then falls. The number of CD4 T lymphocytes falls but stays above 500. In category B individuals, the number of HIV particles in plasma is slowly rising and the number of T lymphocytes is decreasing. In category C individuals, the number of HIV particles in plasma rises dramatically as the number of T lymphocytes falls below 200. At the start of an HIV-1B infection, the virus replicates ferociously, and the killing of CD4 T cells is evident because the blood level of these cells drops dramatically. During the first few weeks of infection, most people develop flulike symptoms (fever, chills, aches, swollen lymph nodes) that may last an average of 2 weeks. After this, a person may remain symptom-free for years, although he or she is still able to pass the virus onto others. At the beginning of this acute phase of infection, an HIV antibody test is usually negative, because it generally takes an average of 25 days before there are detectable levels of HIV antibodies in body fluids. After a time, the body responds to the infection with increased activity of immune cells, and the HIV blood test becomes positive. During this phase, the number of CD4 T cells is greater than the viral load, but some investigators believe that an unseen battle is going on. The body is staying ahead of the hordes of viruses entering the blood by producing as many as 1 to 2 billion new helper T lymphocytes each day. This is called the "kitchen-sink model" for CD4 T-cell loss. The sink's faucet (production of new CD4 T cells) and the sink's drain (destruction of CD4 T cells) are wide open. As long as the body can produce enough new CD4 T cells to keep pace with the destruction of these cells by HIV and by cytotoxic T cells, the person has a healthy immune system that can deal with the infection. In other words, a person in category A has no history of the conditions listed in categories B and C.

Where was HIV originated?

It is generally accepted that HIV originated in Africa and then spread to the United States and Europe by way of the Caribbean. (Recent molecular analyses of the HIV virus suggest that the virus may have first infected humans sometime between 1884 and 1924)

Malaria

Malaria is called the world's invisible pandemic. Most people in the West do not even consider malaria a major health threat, yet in 2015 there were 214 million cases, with over 438,000 deaths, mostly in sub-Saharan Africa. Key to the geographic distribution of malaria is transmission of the disease by a mosquito vector that depends on temperature and rainfall and thus survives well in tropical areas.

Epidemic

More cases of a disease than expected in a certain area for a certain period of time. For example, a few cases of a very rare disease may constitute an epidemic, whereas a larger number of a very common disease may not. If the epidemic is confined to a local area, it is usually called an outbreak. An example was the 2013-2014 Ebola outbreak in West Africa.

Tuberculosis is caused by a bacterial species of the genus

Mycobacterium.

Assembly

New viral particles are made

Describe the differences among an outbreak, an epidemic, and a pandemic, and give an example of each.

Outbreak—when an epidemic is confined to a local area: a cold. Epidemic—a disease with more cases than expected in a certain area during a certain period: the flu. Pandemic—a global epidemic: HIV/AIDS.

People at significant risk for malaria

People at significant risk for malaria include those who have little or no immunity to the parasite. Children, pregnant women, and travelers are most likely to fall victim to the disease. Diagnosis of malaria depends on the presence of parasites in the blood. The incubation period from time of bite to onset of symptoms varies from 7 to 30 days. The symptoms of malaria range from very mild to fatal. Most infected people develop a flulike illness with chills and fevers interrupted by sweating. These symptoms exhibit a cyclical pattern every 48 to 72 hours corresponding to bursting of the red blood cells in the body. Milder cases of malaria are often confused with influenza or a cold; therefore, treatment is delayed. More severe cases cause severe anemia (due to destruction of red blood cells), cerebral malaria, acute kidney failure, cardiovascular collapse, shock, and death.

Malaria is caused by organisms of the genus Plasmodium, which are what type of microbe?

Protists

Select all the ways by which bacterial resistance to antibiotics can be minimized.

Take antibiotics as prescribed until all medication is gone. Only prescribe antibiotics for confirmed bacterial infections.

Ebola outbreak in West Africa

The 2013-2014 Ebola outbreak was largely limited to the countries around West Africa. Additional cases were reported in Nigeria and Senegal, with very isolated cases occurring in Spain, the United States, the United Kingdom, Mali, and Italy.

Initial tests

The Food and Drug Administration (FDA) regulates the terminology associated with at-home testing for diseases such as HIV/AIDS. In general, the term test indicates that a sample (blood, urine) is collected and then sent to a registered lab for analysis. A "rapid test" is performed on-site by a registered health-care worker. In a "home test," the person purchasing the kit collects the samples, performs the tests, and analyzes the results. For a home test, the data are not necessarily verified by a registered health-care worker. Although an Internet search and a visit to almost any drugstore reveal a number of over-the-counter (OTC) home tests for HIV, only two tests are currently approved by the FDA - Home Access HIV-1 Test System—samples blood. - OraQuick In-Home HIV Test—samples oral fluid. These tests may either use blood or oral fluid, but typically a blood sample is preferred because antibodies may be detected in the blood quicker than in oral fluid. Currently, these tests may detect the presence of the HIV virus between 3 and 12 weeks after infection.

Does the TB skin test expose you to tuberculosis?

The TB skin test does not expose you to the Mycobacterium tuberculosis bacterium. Instead, in a lab, a small amount of purified protein derivative (called PPD) is obtained from strains of the bacterium. When the PPD is injected under the skin, it acts as an antigen to the immune system. If you have previously been exposed to TB, the antibody-mediated response will invoke a reaction (swelling, hardness) against the PPD protein. A medical professional familiar with your medical history then measures the degree of the reaction to assess your exposure. Because the PPD protein is derived from the bacterium, it is not capable of causing the disease.

Viral load

The amount of HIV present in an infected person's blood.

Influenza

The common name for influenza is the flu, and each year it affects 5-20% of Americans and causes an estimated 36,000 fatalities. Influenza is a viral infection that causes runny nose, cough, chills, fever, head and body aches, and nausea. You can catch influenza by inhaling virus-laden droplets that have been coughed or sneezed into the air by an infected person, or by contact with contaminated objects, such as door handles or bedding. The viruses then attach to and infect cells of the respiratory tract.

Explain the role of the mosquito in the malarial life cycle.

The mosquito carries the Plasmodium parasite in its salivary gland, which is released when the female mosquito feeds. The parasite completes the sexual part of its life cycle within the mosquito and the asexual part within the human.

Integration

The newly synthesized viral DNA, along with the viral enzyme integrase, migrates into the nucleus of the host cell. Then, with the help of integrase, the host cell's DNA is spliced. Double-stranded viral DNA is then integrated into the host cell's DNA (chromosome). Once viral DNA has integrated into the host cell's DNA, HIV is referred to as a provirus, meaning it is now a part of the cell's genetic material. HIV is usually transmitted to another person by means of cells that contain proviruses. Also, proviruses serve as a latent reservoir for HIV during drug treatment. Even if drug therapy results in an undetectable viral load, investigators know there are still proviruses inside infected lymphocytes.

Plasmodium

The parasites that cause malaria belong to the genus Plasmodium. These are protists (see Fig. 1.6). There are four species that infect humans: P. malariae, P. falciparum, P. vivax, and P. ovale. P. falciparum causes more disease and death than the other species. The parasite is spread by the female Anopheles gambiae mosquito. Half of the life cycle occurs in the human, and the remainder happens in the mosquito. As the female mosquito feeds on human blood, she injects saliva containing an anticoagulant along with the parasite. The parasites travel to the liver, where they undergo asexual reproduction. The parasites are released from the liver to infect more liver cells and erythrocytes (red blood cells). Inside the erythrocyte, the Plasmodium enlarges and divides until it bursts the erythrocyte. This red blood cell stage is cyclic and repeats every 48 to 72 hours. Some parasites within the erythrocytes don't destroy their host cells. Instead, they develop into the sexual form of the parasite. When these are ingested by another mosquito during a blood meal, they develop into male and female gametes within the gut of the mosquito. The gametes fuse, undergo mitosis, and form the parasites that migrate to the salivary glands of the mosquito to continue the cycle.

Human immunodeficiency virus (HIV)

The virus responsible for AIDS. -There are two main types of HIV: HIV-1 and HIV-2. HIV-1 is the more widespread, virulent form of HIV. Of the two types of HIV, HIV-2 corresponds to a type of immunodeficiency virus found in the green monkey, which lives in western Africa. -HIV can infect cells with particular surface receptors. Most importantly, HIV infects and destroys cells of the immune system, particularly helper T cells and macrophages. -As the number of helper T cells declines, the body's ability to fight an infection also declines -AIDS is the advanced stage of HIV infection, in which a person develops one or more of a number of opportunistic infections. An opportunistic infection is one that has the opportunity to occur only because the immune system is severely weakened.

Follow-up tests

These tests are generally performed to confirm a positive result in one of the initial tests. They are always done by a registered lab. Types of lab tests include: Antibody differentiation tests. These distinguish between the presence of the HIV-1 and HIV-2 viruses. Nucleic acid tests. Antigen tests that look for the presence of the RNA associated with the HIV-1 virus. Immunoassays. These are more accurate versions of the antibody tests. As is always the case, it is highly recommended that you talk with your physician regarding the results of any form of medical test.

Reverse transcription

This event in the reproductive cycle is unique to retroviruses. During this phase, the reverse transcriptase enzyme catalyzes the conversion of HIV's single-stranded RNA first into single-stranded DNA (cDNA), and then into double-stranded viral DNA. Usually in cells, DNA is transcribed into RNA. Retroviruses can do the opposite only because they have a unique enzyme from which they take their name (retro in Latin means "reverse").

Currently the number one cause of death in AIDS patients worldwide is

Tuberculosis

Cause of tuberculosis

Tuberculosis is caused by a species of rod-shaped bacterium called Mycobacterium tuberculosis

Explain how variation may occur in influenza viruses such as H5N1.

Variations may result from genetic mutations or from a combining of two different viruses.

The HIV provirus is defined as

Viral DNA inserted into the host genome.

Reverse transcription

Viral RNA genome converted into DNA

Biosynthesis and cleavage

When the provirus is activated, perhaps by a new and different infection, the normal cell machinery directs the production of more viral RNA. Some of this RNA becomes the genetic material for new viral particles. The rest of the viral RNA brings about the synthesis of very long polypeptides. These polypeptides have to be cut up into smaller pieces. This cutting process, called cleavage, is catalyzed by the HIV protease enzyme.

Is malaria curable

Yes, if diagnosed and treated correctly and quickly.

The bacterium that causes tuberculosis is mainly spread by

airborne droplets.

There are generally two types of tests for HIV; those that detect the immune system's response are ______ tests.

antibody

Tuberculosis is likely to be transmitted to caregivers and on long plane flights because

exhaled bacteria can be infectious in the air for hours.

The key factor that determines the distribution of malaria throughout the world is the

presence of the mosquito vector.

A living organism, such as a mosquito, that transfers a pathogen from one host to another is a(n) ______.

vector

The causative agent of influenza is a

virus.