AIDS AND HIV

WHAT IS HIV?

Human immunodeficiency virus (HIV) is the causative agent for AIDS. The most common type is known as HIV-1 and is the infectious agent that has led to the worldwide AIDS epidemic. There is also an HIV-2 that is much less common and less virulent, but eventually produces clinical findings similar to HIV-1. The HIV-1 type itself has a number of subtypes (A through H and O) which have differing geographic distributions but all produce AIDS similarly. HIV is a retrovirus that contains only RNA.

HIV is a sexually transmitted disease. Infection is aided by Langerhans cells in mucosal epithelial surfaces which can become infected. Infection is also aided by the presence of other sexually transmitted diseases that can produce mucosal ulceration and inflammation. The CD4+ T-lymphocytes have surface receptors to which HIV can attach to promote entry into the cell. The infection extends to lymphoid tissues which contain follicular dendritic cells that can become infected and provide a reservoir for continuing infection of CD4+ T-lymphocytes. HIV can also be spread via blood or blood products, most commonly with shared contaminated needles used by persons engaging in intravenous drug use. Mothers who are HIV infected can pass the virus on to their fetuses in utero or to infants via breast milk.

When HIV infects a cell, it must use its reverse transcriptase enzyme to transcribe its RNA to host cell proviral DNA. It is this proviral DNA that directs the cell to produce additional HIV virions which are released.

The genome of HIV contains only three major genes: env, gag, and pol. These genes direct the formation of the basic components of HIV. The env gene directs production of an envelope precursor protein gp160 which undergoes proteolytic cleavage to the outer envelope glycoprotein gp120, which is responsible for tropism to CD4+ receptors, and transmembrane glycoprotein gp41, which catalyzes fusion of HIV to the target cell's membrane. The gag gene directs formation of the proteins of the matrix p17, the "core" capsid p24, and the nucleocapsid p7. The pol gene directs synthesis of important enzymes including reverse transcriptase p51 and p66, integrase p32, and protease p11.

NOW WHAT IS AIDS?

When the CD4 lymphocyte count drops below 200/microliter, then the stage of clinical AIDS has been reached. This is the point at which the characteristic opportunistic infections and neoplasms of AIDS appear. Listed below are some of the more common complications seen with AIDS with images that illustrate gross and microscopic pathologic findings.

The organ involvement of infections with AIDS represents the typical appearance of opportunistic infections in the immunocompromised host--that of an overwhelming infection--that makes treatment more difficult. The strategies employed in AIDS patients to meet this challenge consist of (1) preserving immune function as long as possible with antiretroviral therapies, (2) using prophylactic pharmacologic therapies to prevent infections (such as Pneumocystis carinii pneumonia), and (3) diagnosing and treating acute infections as soon as possible.

THE TWO MOST COMMON DISEASES ASSOCIATED WITH HIV.

1.KAPOSI'S SARCOMA.

Kaposi's sarcoma (KS) is the most common tumor in HIV-infected patients. The appearance of this tumor in young homosexual men in 1981 was one of the first signals of the AIDS epidemic. Caused by a gammaherpes virus called Kaposi's sarcoma-associated herpes virus (KSHV), it often appears as purplish nodules on the skin, but can affect other organs, especially the mouth, gastrointestinal tract, and lungs.

2.PNEUMONIA.
Pneumocystis pneumonia (originally known as Pneumocystis carinii pneumonia, and still abbreviated as PCP, which now stands for Pneumocystis pneumonia) is relatively rare in healthy, immunocompetent people, but common among HIV-infected individuals. It is caused by Pneumocystis jirovecii.

TRANSMISSION.

The three most common transmission routes of HIV are sexual contacts,exposure to infected body fluid and it can also be transmited by mother to fetus.

PREVENTION.

1.Use of condoms during intercourse.
2.Not sharing needles.
3.Discard donated blood that is contaminated with HIV.
4.Circumcision reduce HIV infections.

TREATMENT.

The current choice of treatment is a regimen consisting of two nucleoside inhibitors(zidovudine and lamivudine) and a protease inhibitor(indinavir).This combination is known as HAART.It is very effective in prolonging life but doesnot cure HIV infection.

VACCINE.

No vaccine for human use is available.