Monday, December 10, 2007

Natural history of HIV infection- I

Dr P Saha

HIV is probably the most well known disease to the lay public. Yet the information that the common person has is limited to the fact that it is caused by a virus and is a dangerous disease, and there is some treatment for it which controls the disease but does not cure it. At present it affects about 55 to 60 million people worldwide and already more than 20 million people have died from it. India numerically has the highest number of cases- around 6 million and unfortunately the proportion of people suffering in Manipur is one of the highest in terms of percentage of the population.

In this article we will be discussing the natural history of the disease which means what is the course of events through which the person infected with the HIV goes through. After infection the majority of persons experience a non specific illness which we call primary HIV infection. It is characterized by fever, sore throat, tiredness, muscle pain, lymph node enlargement, and weight loss. About a 1 in 6 such patient requires hospitalization. The symptoms are so non specific that any minor viral illness can mimic them and most of these cases are not diagnosed unless the doctor has a very high index of suspicion. To establish the diagnosis it requires tests which we do not do for suspected HIV cases-normally we do screening serological tests using a method known as ELISA which detects antibodies directed against the HIV virus. For diagnosing primary HIV infection we have to do tests which detect antigen i.e. a substance which is present in the virus and stimulates the body’s immune system or we try to dectect the whole virus. The tests that we do are p24 antigenemia or use a technique known as PCR which detects that whole virus. At the same time we have to show that the ELISA test is negative because the immune system has not yet started reacting to the virus by producing antibody against the HIV virus.

Usually it takes between 2 to 4 weeks for a person to develop primary HIV infection after getting infected by the virus- this period from the time of infection to disease manifestations is known as incubation period. The time taken from the time of infection to the development of antibodies which can be detected with the HIV ELISA test is known as the period of seroconversion and occurs over a period of time. By 6 months more than 95% of the infected persons seroconvert.

Two very important facts have to be known about this disease if the lay person wants to understand this disease- these are viral load and CD4 cell count. Viral load means the number of copies of the virus that are found in the blood per cubic millimetre of blood. It is reported in terms of tens, hundreds, thousands or tens of thousands.

CD4 cells belong to the cells known as lymphocytes which belong to the category of blood cells which we call leucocytes or white blood corpuscles (WBC). The lymphocytes are subdivided into B lymphocytes which for antibodies against infecting organisms (bacteria, viruses, fungi, etc.) and T lymphocytes which attack infecting organisms through a method known as cellular immunity. These T cells are subdivided into helper cells which are known as CD4 cells and suppressor T cells which are known as CD8 cells. HIV is a disease which has a profoundly damaging influence on the T helper cells or the CD4 cells, profoundly decreasing their number and thereby markedly impairing the body’s capability to fight many infections. Normally the CD4 cell count is above 1000 per cubic millimetre. With the passage of time the CD4 cell count starts falling and the greater the fall the higher the chance of the person developing full blown AIDS.

During the primary HIV infection the viral load becomes very high, reaching between 1 lakh to 1 million per cu mm of blood. Subsequently it falls markedly to reach a nadir (lowest count) around 120 days later. Subsequently it starts rising albeit at a low pace. The CD4 count which is around one thousand per cu mm, starts falling and at the end of 6 months it is a little less than 800 and at the end of one year is a little above 650 cells per cu mm. in the subsequent years the fall in CD4 count is around 50 cells per year and the range is around 30 to 90 cells. The disease progresses through a series of stages which seem to correlate with the level of CD4 count.

The primary HIV infection lasts for a period of few days to 3 to 4 weeks. Subsequently the disease goes through the phases of seroconversion, latent period when the patient remains asymptomatic, with or without generalized lymph node enlargement, then comes the early symptomatic HIV disease, then the stage of full blown AIDS and then with advanced HIV infection. These stages will be discussed in the next article.

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The writer is the MD(Medicine) AIIMS, DM (Neurology) AIIMS Consultant Shija Hospital.


Source: http://www.thesangaiexpress.com/Others/Health%20Watch.html

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