My husband has AIDS. Reading one of your articles has made me aware of HIV-1 and HIV-2. What is the difference? How does it affect the patient's life? Does having HIV-1 or HIV-2 make a difference when you get to full-blown AIDS?

N.T.

Two major viruses can cause AIDS, HIV-1 and HIV-2. When most people talk about HIV (the human immunodeficiency virus), they mean HIV-1. Briefly, when someone is infected with HIV-1, after several years of latency (no symptoms), the immune system becomes impaired and the person develops infections, tumors and/or other complications that define AIDS.

HIV-2 is a virus that is similar to HIV-1, but is primarily found in the countries of West Africa, namely Benin, Burkina Faso, Cape Verde, Cote d'Ivoire, Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Mauritania, Niger, Nigeria, Sao Tome, Senegal, Sierra Leone and Togo. HIV-2 is also endemic (common in a geographic area) in Angola and Mozambique. There have been fewer than 100 people with HIV-2 infection described in the United States, all of whom had some contact with people of West Africa. Most of these patients were from that area, others had traveled there and a few (who had never been outside the United States) had contact with natives of West Africa living in the United States.

HIV-2 is less easily spread than HIV-1, either through sex or during pregnancy from an infected pregnant woman to the fetus. Most people with HIV-2 have a lower viral load (amount of virus in the blood), and the infection thus progresses more slowly to AIDS than it does in people with HIV-1. Typically, it takes 7-10 years for a person with HIV-1 infection to develop AIDS.

One difficulty with HIV-2 infection is in its diagnosis. Many diagnostic tests for HIV performed in the United States will not detect patients infected with HIV-2. The ELISA test will miss up to 70 percent of those with HIV-2. For this reason, if the standard HIV tests are negative for a patient in whom we strongly suspect HIV infection, we will request an additional test designed to detect HIV-2. The Centers for Disease Control and Prevention specifically recommends HIV-2 testing for any person suspected of HIV infection who had a potential exposure to anyone from an endemic area in Africa.