This lesson include definition,etiologic agent and life cycle of HIV.

Definition : AIDS was first recognized in the USA in 1981. Prior to identification of HIV it was diagnosed "opportunistic" disease.  It causes defect in cell mediated immunity in the absence of other causes of immunodeficiency. 

The two most important aspect to look in a person is, clinical conditions associated with HIV infection and CD4+ T lymphocyte counts.

Etiologic agent :The causative agent of AIDS is human immunodeficiency virus (HIV) belongs to the family of human retrovirus and subfamily of lentiviruses. There are two distinct groups -: (a) The human T lymphotropic viruses , include HTLV-1 and HTLV-II . (b) HIV-1 and HIV-2.  The most common cause of HIV disease throughout world is HIV-1.

Morphology and life cycle of HIV : HIV virion is an icosahedral structure with numerous external spikes formed by the two major envelope proteins, the external gp120 and the transmembranous ( between two membrane) gp41. HIV is an RNA virus . The life cycle of HIV begins with binding of the gp120 protein on the host cell surface ( CD4 molecule). CD4 molecule is responsible for helper function in our immune system. After binding , fusion with host cell membrane occurs through gp41 molecule. The HIV genomic RNA is uncoated, which is now on its way to target cell present inside the core of our cell known as nucleus. The reverse transcriptase enzyme present in the virion help the viral RNA to change into double stranded DNA which translocate to the nucleus. Here it is integrated into host cell chromosomes with the help of "integrase " enzyme. Now this provirus remain inactive or express gene .The life cycle is shown in the form of  an animation with the assigned netlink of this lesson . It is highly recommended to visit the netlink .

Cellular activation is very important in the life cycle of HIV for effective integration into the host cell genome. Following transcription , HIV mRNA is translated into proteins that undergoes modifications to form progeny virion (babies).  Budding of the progeny virion occurs through host cell membrane .

I hope my first lesson gave you some idea about HIV . The life cycle of HIV is very important as detailed study of its life cycle will help us to eliminate this virus . Each point in the life cycle of HIV is a potential target for treatment . Presently available medicines are blocking the multiplication at two enzyme level, the reverse transcriptase and protease .

This lesson includes various method of transmission. Sexual transmission, blood and blood product transmission,Occupational transmission,Maternal-fetal transmission and transmission by other body fluids.

Sexual Transmission: HIV is predominantly a sexually transmitted disease worldwide. If we talk about USA, half of the reported cases are still among homosexual men. In worldwide heterosexual transmission is the most common mode. HIV is found in seminal and vaginal fluid. If there is, an infection or ulcer in the genital area then the transmission rate will be more. Infection causes increase in white blood cells, the virus is found in lymphocytes and monocytes in large quantity. HIV is found more in the people with sexually transmitted disease. Virus is found in vaginal fluid and in cervical smears. Strongest association is found with anal intercourse, now you will ask me how? (a) Traumatic tears in the anal mucosa (b) Infection of langerhans cells that is found in the mucosal layer of anus.

Lets talk about heterosexual mode of transmission. Do you know that women are more at risk if exposed to an HIV+ compared to men? Let me explain it to you, as exposure time with semen is long in case of women so they are more at risk. People with break in their normal mucosa, genital ulceration with syphilis, herpes or any sexually transmitted disease are at high risk of contracting HIV. Some people ask me about circumcision, as uncircumcised men are at higher risk of genital ulcerative disease, micro trauma during sexual intercourse and in the prepuce, the virus hides itself. All these factors make them more prone to HIV. Most of us think that oral sex is safe sex, actually, it is not true and this is dangerous approach, as there are reports of HIV transmission exclusively through oral sex. So to summarize, any unprotected sexual activity especially with the high-risk groups is considered unsafe.

Transmission by blood and blood products: Think about this mode of transmission, everything is directly or indirectly related with the use of contaminated needles. Individuals who share contaminated needles and syringes for injection drug use and in those who receive transfusions of blood and blood products. Intravenous drug abusers are at high risk. Currently in USA and other developed countries HIV, transmission is very rare through transfusion of blood and blood products. Blood is screened before transfusion. The screening includes ELISA (enzyme linked immunosorbent assay), p24 antigen. Western blots as a confirmatory test wherever applicable.

Occupational transmission: There is small risk of contracting HIV among health care workers; laboratory personnel and the persons dealing with HIV infected specimens. Suppose a laboratory person gets a pinprick from an HIV infected needle, and then the chance of being infected is 0.3%.Now you will ask me what if the lab person who is taking my blood is HIV+ or any health care worker is HIV+. The risk of transmission from infected health care worker to patients is extremely low. Now you will ask me what if accidentally get pricked with a needle used by an HIV+ patient. There are medicines that will decrease your risk of being HIV+. We will discuss all those in coming lessons.

Maternal fetal transmission: Here we are talking about the infected mother. HIV can be transmitted in two ways -: (a) Infected mother to the fetus during pregnancy. (b) During childbirth contracting HIV from mother to the fetus is very high due to the fact that mother gets injuries. We can reduce the risk of mother to fetus transmission by treating mother with Zidovudine. This can be started from 2nd trimester through delivery. Postnatal transmission is reported from colostrums and breast milk so it is advised not to breast feed a newborn of an HIV+ mother, as virus is isolated from these fluids. Women with low CD4+ T cell counts and viremia are at increased risk of transmitting HIV to their infants.

Transmission by other body fluids: HIV can be found in any body fluid but there is no evidence that HIV can be transmitted because of exposure to sweat, tears, saliva and urine. There is no evidence that kissing or hugging transmit HIV although HIV can be isolated from saliva. The virus found in saliva is not enough to transmit HIV. Suppose an HIV+ person has bleeding gums and the other person also has bleeding or break in mucosa then here the transmission is blood to blood not due to saliva. The virus found in saliva is not enough to transmit HIV. Anyway, it will become very complicated so in summary it is better that all bodily wastes of the patients should be handled with universal precautions.

I hope you enjoyed reading lesson 2. I tried to cover the important means of transmission.