Exploring HIV course of infection

Primary HIV infection is defined as the time period from initial infection with HIV to the development of an antibody response detectable by standard tests. Data from careful prospective evaluations of populations at risk for HIV infection demonstrate that up to 87% of individuals who acquire HIV may experience some symptoms of primary HIV infection.

The acute viral syndrome of primary HIV infection (sometimes referred to as “seroconversion illness”) was first defined in 1985, with symptoms resembling those of mononucleosis appearing within days to weeks following exposure to HIV. Symptoms may be mild or severe and may last from a few days to several weeks, with the average duration being 14 days. The most common presenting symptom is fever, seen in over 75% of patients. Other commonly reported symptoms include fatigue, swelling of lymph nodes, headache, and rash.

Evaluation of cohorts from Kenya and India found more frequent reports of joint pains, night sweats, and mucosal candidiasis and less frequent rash and pharyngitis in these study populations.

The median period of time between infection with HIV and the onset of clinically apparent disease is not clearly known as this is mediated by factors such as genetics of resistance to HIV and nutrition. Studies suggest individuals can live with HIV for even more than 10 years.

HIV disease, however, is not uniformly expressed in all individuals. A small proportion of persons infected with the virus develop AIDS and die within months following primary infection, while approximately 5 percent of HIV-infected individuals exhibit no signs of disease progression even after 12 or more years.

Host factors such as age or genetic differences among individuals, the level of virulence of the individual strain of virus, as well as influences such as co-infection with other microbes may determine the rate and severity of HIV disease expression in different people. Such variables have been termed “clinical illness promotion factors” or co-factors and appear to influence the onset of clinical disease among those infected with any pathogen.

As disease progresses, increasing amounts of infectious virus, viral antigens and HIV-specific nucleic acids in the body correlate with a worsening clinical course.

Cross-sectional studies in adults and children have shown that levels of infectious HIV or proviral DNA in the blood are substantially higher in patients with AIDS than in asymptomatic patients.

In both blood and lymph tissues from HIV-infected individuals, researchers at the National Institutes of Health found viral burden and replication to be substantially higher in patients with AIDS than in early-stage patients. This group also found deterioration of the architecture and microenvironment of the lymphoid tissue to a greater extent in late-stage patients than in asymptomatic individuals.

The dissolution of the follicular dendritic cell network of the lymph node germinal center and the progressive loss of antigen-presenting capacity are likely critical factors that contribute to the immune deficiency seen in individuals with AIDS.

It is difficult to identify patients acutely infected with HIV. During acute infection virus predominance may shift from the blood and localize in lymphoid tissues where extremely high rates of virus replication occur.

The U.S. Centers for Disease Control and Prevention (CDC) categorizes HIV-infected adults and adolescents based on their CD4+ counts and clinical conditions.

The CD4+ categories are listed below and correspond to the number of CD4+ cells per microliter of blood: category 1: greater of equal to 500 cells; category 2: 200-499 cells; and category 3: less than 200 cells.

Late signs and symptoms of HIV infection include: the development of Pneumocystis jiroveci pneumonia, toxoplasmosis, cryptosporidiosis, and other opportunistic infections is common.1 Patients may be wasting or losing weight. The viral load continues to increase, and the CD4+ count falls to less than 200 cells per millilitre. These patients have met the definition of AIDS.

Advanced HIV Disease manifests as a continuation of new opportunistic infections such as cytomegalovirus infection, Mycobacterium avium complex, cryptococcal meningitis, progressive multifocal leukoencephalopathy, and other infections that commonly occur secondary to a severely depressed immune system. The viral load is very high, and the CD4+ count is less than 50 cells per millilitre.

June 2006
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