Student presentation on

Human Immunodeficiency Virus (HIV)

By: Mike Peracchio


Life History

The human immunodeficiency virus (HIV) is an obligate intracellular parasite found exclusively in humans. It is responsible for weakening the immune system and leading to acquired immunodeficiency syndrome (AIDS). The first case of AIDS was diagnosed in the U.S. in 1981, and in 1984 it was first proven that HIV caused AIDS. There is currently a pandemic of HIV/AIDS, with the highest incidence rate in Sub-Saharan Africa and the lowest rates in Western Europe and North America, due to better healthcare.

 

Transmission

HIV is spread by sexual contact or blood-to-blood contact. HIV is most commonly spread by sexual contact, including vaginal, anal and oral sex. Another important mode of transmission is the sharing of needles used for intravenous drug use. HIV can be acquired from mother to fetus during pregnancy or from breast milk during nursing. Blood transfusions are becoming a rarer source in developed countries because donated blood is now tested for the presence of HIV. Healthcare workers must take extra precautions because they can contract HIV if stuck by an infected needle or if infected blood contacted their mucous membranes. Individuals with other STDs are at increased risk of contracting HIV.


Microbiological Characteristics and Virulence Factors

HIV is a retrovirus with a genome consisting of two identical RNA molecules linked in a dimeric structure. Retroviruses use an enzyme called reverse transcriptase to synthesize DNA that is then incorporated into the genome of the host cell, forming a provirus. HIV belongs to a subgroup known as lentiviruses (“slow” viruses) that have a long period of time between the initial infection and the onset of serious symptoms. HIV is a spherical virus with an envelope comprised of a lipid bilayer and surface glycoproteins, gp120 and gp41, that attach to host cell receptors, CD4 and CCR5. HIV primarily attacks CD4+ helper T cells by recognizing and binding the CD4 receptor on the surface of the T cells. It can sometimes invade monocytes and macrophages as well since they also have some CD4 receptors on their surfaces. Tumor necrosis factor alpha (TNF-a) and interleukin-6 (IL-6) are secreted at higher levels in infected individuals, and this may help activate the HIV proviruses (latent viruses). HIV has a high mutation rate during replication with the reverse transcriptase, which is why it is able to readily evade our immune response.

Disease

HIV causes the gradual weakening of the immune system which can culminate in acquired immunodeficiency syndrome (AIDS). About 2-4 weeks after initial infection with HIV there are generally flu-like symptoms that usually resolve themselves in a couple of weeks. The infected person then may go asymptomatic for a long time, often many years. The average development of AIDS in western nations, if untreated, is about 10-12 years after the initial infection of HIV. Persons with AIDS experience fatigue and excessive weight loss, along with fever, night sweats and swollen lymph nodes. The immune system is highly diminished in AIDS patients making them susceptible to many opportunistic diseases such as pneumonia caused by Pneumocystis carnii. AIDS patients can also develop neurological disorders and certain cancers associated such as Kaposi’s sarcoma and certain lymphomas.

Diagnosis and Treatment

HIV is diagnosed by blood tests involving two or more positive ELISA (enzyme linked immunosorbent assay) tests that have been confirmed by a Western blot assay. The level of CD4+ helper T cells is counted as well. A normal CD4+ count is 800-1200 cells/mm3, but for people with HIV the count is usually under 350 cells/mm3 in HIV patients. AIDS is generally considered the state at which the CD4+ count drops below 200 cells/mm3. HIV is usually treated with three or more antiretroviral medications, of which there are two main types: protease inhibitors and reverse transcriptase inhibitors. The combination of medications acts to slow down the degeneration of the immune system, but there is currently no treatment that will destroy or completely prevent the spread of HIV. The best defense against HIV is prevention, which is best accomplished by abstaining from sexual intercourse or at least by using male latex condoms and limiting the number of sexual partners. Intravenous drug use and the sharing of needles should also be avoided. There is a need for greater education and awareness of how to best prevent HIV infection. There is also a need to try and lower the cost of prevention and treatment to make these methods available to developing nations where the problem is greatest.

Epidemiology

HIV is most prevalent among individuals aged 15-49, as they are the most sexually active. In adults worldwide, infection of men and women is about equal, however in men the most common mode of transmission is through homosexual sex, followed by heterosexual sex and intravenous drug use, whereas for women heterosexual intercourse is most common followed by intravenous drug use. In the U.S., new HIV cases each year occur about 70% among men and 30% among women, with half of these new cases in people under 25.Of the approximately 42 million cases of HIV/AIDS worldwide, Sub-Saharan Africa has the vast majority (70%), followed by Southeast Asia (17%) and other developing nations with lower opportunities for proper healthcare. In the U.S., it is estimated that 850,000-950,000 people are living with HIV infection. HIV infection is more common in African-Americans, especially in adolescents. HIV/AIDS is now the second leading cause of death worldwide, and the fifth leading cause of death in Americans aged 25-49. It is the leading cause of death of African Americans in this age group.

Sources:
http://www.avert.org/worldstats.htm
http://www.cdc.gov/hiv/dhap.htm
http://www.niaid.nih.gov/factsheets/aidsstat.htm
http://my.webmd.com/content/healthwise/19/4774
http://my.webmd.com/content/healthwise/141/35035