HIV is the abbreviation for human immunodeficiency virus. HIV is a retrovirus that infects and gradually destroys cells in the immune system and may eventually lead to AIDS (acquired immunodeficiency syndrome). There are two closely related viruses: HIV-1, which is the most common cause of AIDS throughout the world; and HIV-2, which is largely confined to West Africa.

Methods of transmission 

HIV is transmitted in body fluids, such as blood, semen, and vaginal secretions. It most commonly gains access to the body during sexual activity (either vaginal, anal, or oral), particularly when contaminated body fluids come into contact with broken skin. Other sources of infection are nonsterile needles (for example, among people who abuse intravenous drugs and share needles and syringes) and, in some parts of the world, contaminated blood transfusions. In addition, if a pregnant women is infected, the virus can pass to the fetus via the placenta. It is not transmitted by everyday physical contact such as shaking hands or hugging.

Effects of the virus 

HIV infects cells that have a special structure, called a CD4 receptor, on their surface. This includes immune system cells called CD4 lymphocytes, which defend the body against cancerous and infected cells, as well as certain cells in other tissues, such as the brain.The virus multiplies within the cells, killing them in the process; the dead cells then release more virus particles into the blood. If the virus is untreated, the number of CD4 lymphocytes falls. This results in a reduced ability to fight off infections and certain types of cancer.

HIV is extremely successful at withstanding any attempt by the body to destroy it. Every time HIV replicates, it changes its antigen makeup, thereby ensuring that it is extremely difficult for the body to mount an effective immune response to it.


Initially, some people who are infected with HIV may have no symptoms. However, between six and eight weeks after exposure, some people develop a flulike illness similar to glandular fever (see mononucleosis, infectious), with fever, fatigue, sore throat, aching muscles, and swollen lymph nodes. These symptoms usually clear up after a few weeks. Some people may then develop persistent enlargement of the lymph nodes and sometimes of the spleen, as well as features of AIDS-related complex, such as weight loss and fever.

Minor features of infection with HIV include skin disorders such as seborrhoeic dermatitis. More severe features include persistent herpes simplex infections, oral candidiasis (thrush), herpes zoster (shingles), tuberculosis, and shigellosis (bacterial infection of the intestine). HIV may also affect the brain, causing a variety of neurological disorders, including dementia.

If HIV infection is untreated, the infected person may eventually develop full-blown AIDS. In this condition, the immune system is severely weakened, resulting in severe infections caused by organisms that are usually harmless as well as in certain types of cancer.

Diagnosis, treatment and outlook 

HIV is diagnosed through an HIV test, a blood test that detects the presence of antibodies (proteins manufactured by the immune system) to HIV in the blood.

People infected with HIV should have regular monitoring in order to determine when specific treatments, such as antiretroviral drugs, are necessary. The main types of antiretroviral used are protease inhibitors, such as indinavir and lopinavir, and reverse transcriptase inhibitors, such as zidovudine. These drugs can slow the course of the disease and may prevent the development of full-blown AIDS.

In wealthier countries, HIV infection is no longer necessarily a fatal disease. It remains life-threatening, however, and the most effective strategy for defeating it is prevention of infection.


The risk of infection with HIV can most easily be reduced by practising safer sex. Intravenous drug users should take care not to share needles. Others who may be at risk, such as healthcare workers who may come into contact with infected body fluids or needles, should observe recommended safety regulations.

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