A long-term infection that, left untreated, results in reduced immunity to other infections
- Unprotected sex and intravenous drug use are risk factors
- Age, gender, and genetics are not significant factors
Infection with the human immunodeficiency virus (HIV), which can lead to acquired immunodeficiency syndrome (AIDS) if left untreated, has been one of the most written about and researched diseases of recent years. Despite the development of effective drugs to limit the progression of the infection, there is still no effective vaccine against the virus, and the number of people with HIV infection continues to rise, especially in developing countries.
HIV is believed to have originated in Africa, where a similar virus is carried by some species of primate. The virus is thought to have spread from monkeys to humans, then around the world from person to person by sexual contact or through other exchange of body fluids. The first recognized cases of AIDS occurred in 1981, when there was an outbreak of unusual cases of pneumonia and skin cancer in young homosexual men in Los Angeles. Two years later, the causative virus was isolated and identified as HIV.
HIV infects and gradually destroys cells in the immune system, weakening the response to infections and cancers. People infected with HIV may have no symptoms for years, or may experience frequent or prolonged mild infections. When the immune system becomes severely weakened, people are susceptible to serious infections caused by organisms that are usually harmless, and also to certain types of cancer. The development of some specific diseases or cancers leads to a diagnosis of AIDS.
Who is affected?
At the end of 2007, there were an estimated 77,400 people in the UK living with HIV/AIDS, of whom about 21,700 were not aware they were infected. About 7,700 new cases of HIV infection were diagnosed in the UK in 2007. Worldwide in 2007 there were an estimated 33 million people with HIV/AIDS, of whom about 22 million were living in sub-Saharan Africa; 2.7 million new cases were diagnosed during that year.
In the mid-1990s more effective antiviral drug therapy became available, as a result of which the number of deaths from HIV/AIDS in the developed world diminished significantly; in the UK, for example, deaths reduced from more than 1,700 in 1995 to around 250 in 2008. However, antiviral therapy is complex, expensive, and requires detailed monitoring of patients, and therefore therapy was initially limited to patients in wealthier countries. More recently, access to antiviral therapy has improved in some developing countries. Nevertheless, almost 2 million people still died from HIV/AIDS in developing countries in 2007.
How is HIV transmitted?
In people infected with HIV, the virus is present in body fluids, including blood, semen, vaginal secretions, saliva, and breast milk. It is most commonly transmitted sexually, by anal, oral, or vaginal intercourse. People are at higher risk of HIV infection and more likely to transmit the virus if they have another sexually transmitted infection.
People who use intravenous drugs and share or reuse needles contaminated with the virus are at high risk of infection. Medical workers are also at risk from accidental skin punctures with contaminated needles (see Needlestick injury), but the risk is low.
HIV infection can be passed from an infected woman to the fetus or to the baby at birth (see Congenital infections) or by breast-feeding. The virus can be transmitted through organ transplants or blood transfusions, but in developed countries, routine screening of blood, organs, and tissues for HIV has made the risk of infection by these routes extremely low. HIV infection cannot be transmitted by everyday contact, such as shaking hands, or by coughs or sneezes. There is no risk to your health from working or living with an infected person.
What is the cause?
HIV enters the bloodstream and infects cells with a special structure called the CD4 receptor on their surfaces. These cells include a type of white blood cell known as a CD4 lymphocyte, which is responsible for fighting infection. The virus reproduces rapidly within the cells and destroys them in the process.
At first, the immune system is able to function normally, and symptoms may not develop for years. However, the number of CD4 lymphocytes eventually falls, causing susceptibility to other infections and some types of cancer.
What are the symptoms?
The first symptoms of HIV infection can appear within 6 weeks of the virus entering the body. Some people experience a flu-like illness that may include some or all of the following symptoms:
Swollen lymph nodes (see Lymphadenopathy).
Tiredness and aching muscles.
These symptoms usually clear up after a few weeks, and many people with HIV infection feel completely healthy. However, in some people, any of the following minor disorders may develop:
Persistent, swollen lymph nodes.
Mouth infections such as thrush (see Candidiasis).
Furred white patches in the mouth (see Oral leukoplakia).
Gum disease (see Gingivitis).
Extensive genital warts.
Itchy, flaky skin (see Seborrhoeic dermatitis).
The time between infection with HIV and the onset of AIDS varies and can be between 1 and 14 years. Often, people are unaware for years that they are infected with HIV until they develop one or more serious infections or cancers known as AIDS-defining illnesses.
Are there complications?
The single complication of HIV infection is the development of AIDS. A person infected with HIV is said to have AIDS if he or she has developed a particular AIDS-defining illness. These illnesses include opportunistic infections (infections that occur only in people with reduced immunity), certain cancers, and nervous system disorders that may result in dementia, confusion, and memory loss.
These infections may be caused by protozoa, fungi, viruses, or bacteria, and they can often be life-threatening.
One of the most common illnesses in people with AIDS is a severe infection of the lungs by the parasite Pneumocystis jiroveci (see Pneumocystis infection). Other common diseases are the protozoal infections cryptosporidiosis, which may result in prolonged diarrhoea, and toxoplasmosis, which can affect the brain.
Candida albicans is a fungus that can cause mild superficial infections in healthy people but may produce much more serious infections in people who have developed AIDS (see Candidiasis). The cryptococcus fungus (see Cryptococcosis) may cause fever, headaches, and lung infections.
People with AIDS suffer from severe bacterial and viral infections. Bacterial infections include tuberculosis and salmonellosis, which may lead to blood poisoning (see Septicaemia). Viral infections include those caused by the herpes viruses. Herpes simplex infections can affect the brain, causing meningitis and viral encephalitis. Cytomegalovirus infection may cause a number of severe conditions, including pneumonia, viral encephalitis, and a type of eye inflammation that can result in blindness. However, people who have AIDS are not more susceptible to common infections such as colds.
The most common type of cancer that affects people with AIDS is Kaposi’s sarcoma, a type of skin cancer that can also affect the inside of the mouth and internal organs, including the lungs. Other types of cancer that commonly develop in people with AIDS include lymphomas, such as non-Hodgkin’s lymphoma. Cancer of the cervix is an AIDS-defining illness in women infected with HIV.
How is it diagnosed?
If you suspect that you may have been exposed to HIV infection, you should have a blood test to check for antibodies against the virus. You may also have this blood test if you have symptoms that suggest HIV infection, and it is often offered as part of antenatal care. Consent is always obtained before the test, and counselling is given both before and afterwards to discuss the implications of a positive result.
If your HIV test result is negative, you may be advised to have another test in 3 months because antibodies take time to develop. HIV infection can also be difficult to diagnose in the baby of an infected woman because the mother’s antibodies may remain in the baby’s blood for up to 18 months.
AIDS is diagnosed when an AIDS-defining illness, such as pneumocystis infection, develops or when a blood test shows that the CD4 lymphocyte count has dropped below a certain level.
What is the treatment?
If your HIV test result is positive, you will probably be referred to a special centre where you will receive monitoring, treatment, and advice from a team of health-care professionals.
Drug treatment may be started when you are diagnosed with HIV infection, or when blood tests show that virus levels are increasing or that the CD4 lymphocyte level is falling. Advances in the use of combinations of specific antiviral drugs that stop HIV from replicating have made it possible to prevent progression of HIV infection to AIDS and to suppress the viral infection to undetectable levels in some people (see Drugs for HIV infection and AIDS).
Once AIDS has developed, opportunistic infections are dealt with as they occur. In some cases, there may also be long-term preventive treatment against the most common infections. Emotional support and practical advice can be obtained from the many groups and charitable organizations that help people with HIV infection and AIDS.
What is the prognosis?
There is no cure for HIV infection, but the drug treatments available in the developed world have made it possible to regard the condition as a long-term illness rather than a rapidly fatal one. Since the introduction of antiviral drug combination therapies, deaths from AIDS in the developed world have been reduced dramatically. In the developing world, although advances have been made in delivering care, many people still have limited access to such care and HIV/AIDS remains a major cause of illness and premature death.
Can it be prevented?
HIV infection can be prevented by teaching at an early age about the risks of infection. The two main precautions that everyone can take to avoid sexual transmission are to use a condom during sexual intercourse and to avoid sex with multiple partners (see Sex and health). It is also recommended that both partners have an HIV test before having unprotected sex in a new relationship. Specific groups need to take special precautions. For example, people who inject drugs intravenously must use a clean needle and syringe every time.
People who are HIV positive need to take special care to prevent others from coming into contact with their blood or body fluids and should always inform dental or medical staff that they have HIV infection. Women who are HIV positive and pregnant may be given antiviral drugs to reduce the risk of transmission to the fetus, and they may also be advised to have a caesarean section and avoid breast-feeding to reduce the risk of transmitting the virus to their babies.
Medical professionals take many steps to prevent transmission of HIV, including screening all blood products and tissues for transplant and using disposable or carefully sterilized equipment.
Extensive research is being carried out to develop a vaccine against HIV and to prevent the development of AIDS. However, although researchers are optimistic they will succeed, there will inevitably be millions more deaths worldwide before an affordable cure is found and made widely available.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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