HIV-infected people are generally defined as having Aids when their CD4+ T-cell count has fallen to less than 200. In addition there are various clinical conditions which are thought of as Aids-defining illnesses.

HIV itself does not kill. It is the infections and illnesses that result from the body's inability to fight these due to the depressed immune system which can kill.

Kaposi's sarcoma

Kaposi's sarcoma was one of the first illnesses noticed among San Francisco gay men in the early 1980s. It was then a little-known disease of elderly European men and young Africans, which tended to be chronic and rarely spread through the body.

It presents clinically as purple, vascular nodules on the skin. It may remain as nothing more than skin patches, or it can become a serious illness with involvement of the major organs. The most common involvement is in the lymph nodes, gastrointestinal tract and the lungs.

If there is nothing more than skin involvement and the lesions are not cosmetically unacceptable, then no treatment is necessary. However, with greater skin spread, or involvement of major organs, then radiotherapy and chemotherapy are used, with some success, although in advanced disease the respite is generally temporary. One of the main problems with both forms of treatment in Aids patients is that a further insult to the immune system is delivered by the treatment itself, compounding the effects of HIV.

Lymphoma

Certain of the lymphomas are more common in HIV positive people. There is an increased incidence of high-grade (more serious) non-Hodgkin's lymphomas, including lymphoma of the brain. These lymphomas are particularly aggressive with a high mortality.

Hodgkin's disease in HIV-infected people tends to be atypically aggressive, involving multiple sites.

Pneumocystis carnii pneumonia

This is one of the commonest HIV related illnesses and anyone who is HIV positive should be on regular prophylaxis against the illness with Bactrim® (trimethoprim-sulphamethoxazole).

This is an opportunistic pathogen with lives naturally in the lungs. It only becomes a problem when its host, the human, has problems with the immune system. Hence its prevalence in HIV infected people.

Infection presents with fever, shortness of breath and a non-productive cough. HIV-positive persons are typically ill for a few weeks, but may often have subtle symptoms for a few months. It may be a difficult diagnosis to make and an HIV-positive person with a cough should be assessed carefully, rather than treated symptomatically.

Pneumocystis is generally confined to the lungs, but there are cases of infection spreading though the body.

Treatment should be started as early as possible in the illness. The two major drugs used are Bactrim and pentamidine. These two drugs are equally effective and the overall success rate of treatment is 70 to 80 percent. Bactrim is given orally or intravenously, while pentamidine is given either intramuscularly or intravenously.

Bactrim has few side effects in non-HIV-positive people, but more than 50 percent of HIV-positive patients have serious side effects including fever, rash and blood problems. However, recently it has been found that HIV-positive patients can be desensitised to Bactrim by giving low doses initially, building up to the standard dose over time.

Treatment is prolonged to a minimum of 21 days in Aids patients, since they tend to improve only slowly.

The recurrence rate in HIV-positive people is about 50 percent at 1 year, and for those who cannot tolerate Bactrim, or have had previous episodes of P. carnii pneumonia, pentamidine can be used via a nebuliser.

Candida albicans

Candidiasis, or thrush, is common in HIV-positive patients, and is an Aids-defining condition. It is generally seen in the mouth, affecting the oropharynx, and can extend down into the oesophagus.

Symptoms are a rough feeling and pain on the soft palate, and pain on swallowing.

Anti-fungal agents such as Sporanox® (itraconazole), or Diflucan® (fluconazole) are effective. Sporanox is now available as a liquid as well as a tablet. Oral Nystatin® can also be used but is not as effective in HIV positive people.

People with Aids are at risk of developing disseminated candidiasis, in which the fungus spreads through the body. The symptoms are frequently non-specific, with fever, shock, and renal failure. The heart may be involved with infection of the valves (endocarditis), and there can also be a candida meningitis. These serious complications require intensive care and treatment is supportive and with amphotericin B.

Cytomegalovirus

Cytomegalovirus (CMV) is one of the herpesvirus group. It is almost ubiquitous in people with Aids, and often causes retinitis (leading to blindness) and disseminated disease, which kills.

CMV-mediated immunosuppression probably contributes to the T-cell deficiency in HIV.

CMV infection is often heralded by prolonged fever, malaise, lack of appetite, fatigue, night sweats and muscle and joint pains. During these episodes any investigations of liver functions and blood indices will be abnormal.

CMV can involve the lungs, gastrointestinal tract, brain and retina. This latter is an important cause of blindness among Aids patients.

Recent work has suggested that giving Aids patients oral gancyclovir (Cymevene®) along with a tiny pellet of the same drug implanted in the eye delays or prevents complications of CMV. However, this treatment is very expensive and only available to a few.

New drugs to combat CMV retinits are currently under development, some with promising results.

Toxoplasmosis

Toxoplasma gondii is an infection caused by a protozoan parasite. It has a wide distribution and is associated with cats' faeces and eating undercooked meat which may contain T. gondii cysts. The infection is uncommon, except in those who are immunocompromised and in pregnant women, where it carries a risk of foetal infection and congenital abnormalities.

Any HIV-positive person or pregnant woman who keeps cats should make sure that they wear gloves when gardening, and also when emptying litter trays. All meat should be cooked thoroughly.

Generally, if a person who is not immunocompromised is exposed to T. gondii, the infection remains asymptomatic and latent since their immune systems can deal with the infection adequately. However, this is not the case in those with HIV infection, who may present with a variety of manifestations of the disease, such as toxoplasma encephalitis, retinitis, pneumonitis and also a disseminated form of the disease in which may affect all organ systems in the body.

Toxoplasma encephalitis is the most common manifestation of the disease, presenting as single or multiple brain abscesses. Sixty to 70 percent of patients have fever and headaches. Some present with focal neurological signs such as weakness or inability to move one side of the body, difficulties with speech, or difficulty walking which may mimic a stroke. Other neurological signs may include confusion, lethargy and seizures.

Diagnosis is by demonstrating the parasite in tissue or body fluids. However, because T. gondii encephalitis is such a common manifestation of the onset of Aids, a presumptive diagnosis is often made with a combination of clinical findings and characteristic lesions in the brain on CT or MRI scanning.

Treatment is divided into initial therapy in which the acute infection is dealt with by 4 to 6 weeks of maximal doses of the appropriate drugs. This is followed by so-called suppressive therapy in which lower doses of the drugs are used indefinitely to prevent further reactivations.

Commonly used drugs are combinations of sulphadiazine-pyrimethamine and pyrimethamine-clindamycin. Other drugs used are clarithromycin and azithromycin. Cotrimoxazole, dapsone-pyrimethamine or dapsone-trimethoprim are used for prophylaxis.