Acquired immune deficiency syndrome, a deficiency of the immune system due to infection with the human immunodeficiency virus. HIV being the common abbreviation. Highly variable is the interval between infection and the development of AIDS. Without treatment around half of those individuals infected would develop AIDS within 8- 9 years. However in about one in ten cases progression to AIDS is very slow, taking up to 20 years or longer. There is as yet, no cure or vaccine even though illness and death from AIDS is a major health problem worldwide.
Methods of transmission]
HIV is transmitted in body fluids such as blood, semen, vaginal secretions and breast milk. Key methods of transmission are sexual contact (anal, oral or vaginal), blood to blood (via transfusions or needle sharing in drug users) and mother to foetus. HIV is also transmitted through blood products given to treat haemophilia, kidney transplants and artificial insemination by donated semen; but better screening has heavily reduced these risks. HIV cannot be spread by everyday contact such as sharing crockery or hugging.
Effects of the virus
The virus enters the bloodstream and infects cells with a particular receptor, named the CD4 receptor, on their surface. These cells can include a type of white blood cell called a CD4 lymphocyte (a T-lymphocyte with a CD4 receptor) that is responsible for attacking infection and cells in other tissues such as the brain.
Within the affected cells the virus reproduces. The cells which then die, releasing more virus particles into the blood. If the infection is left untreated the number of CD4 lymphocytes falls, creating a greater susceptibility to particular infections and some types of cancer.
Symptoms and signs
Certain people experience a short lived illness similar to infectious mononucleosis when they are initially infected with HIV. A great number of individuals have no obvious symptoms but are nonetheless infectious. After the initial illness many people remain well. Some can suffer from enlarged lymph nodes, extreme sweating and muscle pain. Relentless bacterial infections such as pneumonia are common. Later, vague complaints, such as fevers, sweats, weight loss or unexplained diarrhoea may indicate the development of AIDS.
Skin disorders such as, seborrhoeic dermatitis and a range of viral, bacterial and fungal infections, such as unrelenting herpes simplex infections, tuberculosis, oral candidiasis (thrush) and shigellosis are other features of infection with HIV. HIV can also affect the brain, causing an array of neurological disorders, included in that is dementia.
Particular conditions, known as AIDS defining illnesses, mark the development of full blown AIDS. These include various infections (pneumocystis pneumonia, tuberculosis, human papillomavirus, cytomegalovirus infection, toxoplasmosis, diarrhoea due to Cryptosporidium or Isopora, candidiasis, disseminated strongyloidiasis, and cryptococcosis) and cancers (kaposi’s sarcoma and lymphoma of the brain); many of these are described as opportunist infections.
To confirm HIV infection a blood test is needed to test a blood sample for the presence of anti bodies to HIV, which cannot always develop straight away and can take up to three months or more after initial infection. The condition is monitored using blood tests that measure the number of CD4 lymphocytes in the blood or by measuring viral load (the amount of virus detectable in the blood). Diagnosis of full-blown AIDS is based on a positive HIV test along with the presence of an AIDS defying illness. Occasionally people only realise they have HIV when they develop an AIDS- defining illness and then have an HIV test.
Treatment and outlook
There can be two separate treatments for HIV infection. One being for the HIV infection itself and the other for the treatment of conditions and complications that are related to HIV/AIDS.
Occasionally the progress of the disease can be slowed or even prevented from developing into full-blown AIDS. This is done with a combination of antiretroviral drugs which reduce the amount of virus in the blood stream. The two common types of antiretroviral drugs are reverse transcriptase inhibitors, such as zidovudine, and protease inhibitors, such as indinavir. These groups of drugs work by disrupting replication of HIV inside cells. Several drugs are often used in combination in a regime known as highly active antiretroviral therapy or HAART for short. The emergence of resistant strains of HIV has lead to the development of a new group of drugs called fusion inhibitors (example being, enfuvirtide) which work by interfering with the entry of the virus into cells. The mainstay of treatment for HIV/AIDS- related illnesses consists of antifungals, antibiotics and other antimicrobial drugs to treat particular infections as they develop.
Death from AIDS in the developed world has significantly dropped, since the introduction of combination drug therapy. However unfortunately, such therapy is not a cure and HIV-infected people are still infectious even when the infection is being controlled successfully with drug treatment. Hence the most effective strategy for defeating HIV/AIDS remains prevention of infection.
Prevention of infection
Safer sex can reduce the risk of infection, and by intravenous drug users not sharing needles. There is a slight risk to health workers handling contaminated needles (example, needlestick injuries) or blood products, but this can be minimized by adopting safe practices in the workplace.