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Opportunistice Infections

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There are two main types of candidiasis: localised disease (of the mouth and throat or of the vagina) and systemic disease (of the oesophagus, and disseminated disease). The mouth and throat variant (commonly known as thrush or OPC) is believed to occur at least once in the lifetime of all HIV-infected patients. Occurence of the vaginal variant is common among healthy women and is unrelated to HIV status.

While OPC is not a cause of death, it can cause oral pain and make swallowing difficult. The main symptom is creamy white legions in the mouth that can be scraped away. Oesophageal (gullet) candidiasis is a more serious condition which can cause pain in the chest that increases with swallowing. Disseminated candidiasis causes fever and symptoms in the organs affected by the disease (for example, blindness when it affects the eyes), and can be life threatening.

Localised disease may be treated at first with relatively inexpensive drugs such as nystatin, miconazole or clotrimazole. Systemic candidiasis requires treatment with systemic antifungal agents such as fluconazole, ketoconazole, itraconazole or amphotericin.

Cryptococcosis

Cryptococcosis is caused by a fungus that primarily infects the brain. It most often appears as meningitis and occasionally as pulmonary or disseminated disease. Untreated cryptococcal meningitis is fatal.

Cryptococcosis is relatively easy to diagnose. However, its treatment (either amphotericin B with or without flucytosine or in mild cases with oral fluconazole) and secondary chemoprophylaxis are often impossible in developing countries because of high cost and limited availability of the drugs required.

Cryptosporidiosis and isosporiasis

Cryptosporidiosis (crypto) and isosporiasis are both caused by protozoan parasites. These diseases are easily spread by contaminated food or water, or by direct contact with an infected person or animal. Both crypto and isosporiasis cause diarrhoea, nausea, vomiting and stomach cramps. In people with healthy immune systems, these symptoms do not last more than about a week. However, if the immune system is damaged then they can continue for a long time. Diarrhoea can interfere with the absorption of nutrients and this can lead to serious weight loss.

To confirm diagnosis of either disease, the stool is normally checked for parasites and their eggs. There is no cure for crypto, but antiretroviral therapy to restore immunity can effectively clear up the infection. For isosporiasis, TMP-SMX (trimethoprim-sulfamethoxazole) is often the preferred treatment.

Cytomegalovirus

Cytomegalovirus (CMV) is a virus that infects the whole body. It most commonly appears as retinitis, which causes blurred vision and can lead to blindness. CMV can also affect other organs, and is capable of causing fever, diarrhoea, nausea, pneumonia-like symptoms and dementia.

CMV infection may be treated with drugs such as ganciclovir, valganciclovir and forscarnet.

Herpes simplex and Herpes zoster

The usual symptoms of herpes simplex virus infection (HSV, which causes sores around the mouth and genitals) and herpes zoster virus infection ('zonal' herpes or shingles) are not life-threatening but can be extremely painful. Both viruses are also capable of causing retinitis and encephalitis (which can be life-threatening).

Both herpes simplex and herpes zoster are usually diagnosed by simple examination of the affected area, and may be treated with drugs such as acyclovir, famciclovir and valacyclovir.

Histoplasmosis

Histoplasmosis is a fungal infection that primarily affects the lungs but may also affect other organs. Symptoms can include fever, fatigue, weight loss and difficulty in breathing.

Disseminated histoplasmosis infection may be diagnosed using an antigen test, and can be fatal if left untreated. Treatment usually involves amphotericin B or itraconazole.

Kaposi's sarcoma

HIV-associated Kaposi's sarcoma causes dark blue lesions, which can occur in a variety of locations including the skin, mucous membranes, gastrointestinal tract, lungs or lymph nodes. The lesions usually appear early in the course of HIV infection.

Treatment depends on the lesions' symptoms and location. For local lesions, injection therapy with vinblastine has been used with some success. Radiotherapy can also be used, especially in hard-to reach sites such as the inner mouth, eyes, face and soles of the feet. For severe widespread disease, systemic chemotherapy is the preferred treatment.

Leishmaniasis

Leishmaniasis is transmitted by sandflies and possibly through sharing needles. The most serious of its four forms is visceral leishmaniasis (also know as kala azar) which is characterised by irregular bouts of fever, substantial weight loss, swelling of the spleen and liver and anaemia (occasionaly serious). In its more common forms, leishmaniasis can produce disfiguring lesions around the nose, mouth and throat, or skin ulcers leading to permanent scarring.

Treatment of leishmaniasis with pentavalent antimony is relatively expensive, partly because of the cost of drugs but also because hospital admission is recommended (in milder cases, trained health workers may administer the injections or infusions at a patient's home). If left untreated, visceral leishmaniasis is usually fatal.

MAC

The germs of the mycobacterium avium complex (MAC) are related to the germ that causes tuberculosis. MAC disease generally affects multiple organs, and symptoms include fever, night sweats, weight loss, fatigue, diarrhoea and abdominal pain.

MAC should be treated using at least two antimycobacterial drugs to prevent or delay the emergence of resistance. Such drugs include clarithromycin, azithromycin, ethambutol and rifabutin.

PCP

PCP is caused by a parasite that infects the lungs, which was formerly called pneumocystis carinii but has now been renamed pneumocystis jiroveci. PCP is a frequent HIV associated opportunistic infection in industrialised countries but appears to be less common in Africa. The symptoms are mainly pneumonia along with fever and respiratory symptoms such as dry cough, chest pain and dyspnoea. Definitive diagnosis requires microscopy of bodily tissues or fluids.

Severe cases of PCP are initially treated with TMP-SMX or clindamycin and oral primaquine. Mild cases can be treated with oral TMP-SMX throughout. With both of these regimens, toxicity (notably allergic-type reactions) often requires changes in therapy.

Prevention of PCP is strongly recommended for HIV-infected persons with very weak immune systems wherever PCP is a significant health problem for HIV-infected persons, and also after their first episode of PCP. The preferred drug is usually TMP-SMX.

Toxoplasmosis

Toxoplasmosis (toxo) is caused by a protozoan found in uncooked meat and cat faeces. This microbe infects the brain and can cause headache, confusion, motor weakness and fever. In the absence of treatment, disease progression results in seizures, stupour and coma. Disseminated toxo is less common, but can affect the eyes and cause pneumonia.

Definitive diagnosis of toxo requires radiographic testing (usually a CT or MRI scan). The infection is treated with drugs such as pyrimethamine, sulfadiazine and clindamycin. Leucovorin may also be used to prevent the side-effects of pyrimethamine.

Tuberculosis

Tuberculosis (TB) is a bacterial infection that primarily infects the lungs. Tuberculosis is the leading HIV-associated opportunistic disease in developing countries. For people who are dually infected with HIV and TB, the risk of developing active tuberculosis is 30-50 fold higher than for people infected with TB alone. And because mycobacterium can spread through the air, the increase in active TB cases among dually infected people means:

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more transmission of the TB germ
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more TB carriers
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more TB in the whole population.

Tuberculosis is harder to diagnose in HIV-positive people than in those who are uninfected. The diagnosis of TB is important because TB progresses faster in HIV-infected people. Also, TB in HIV-positive people is more likely to be fatal if undiagnosed or left untreated. TB occurs earlier in the course of HIV infection than many other opportunistic infections.

A proper combination of anti-TB drugs achieves both prevention and cure. Effective treatment quickly makes the individual non-contagious, which prevents further spread of the TB germ. The DOTS (directly observed short course) treatment strategy recommended by WHO treats TB in HIV-infected persons as effectively as it treats those without the virus. A complete cure takes 6 to 8 months and uses a combination of antibiotics. In addition to curing the individual, it also prevents further spread of the disease to others. This is why treating infectious cases of TB has important benefits for society as a whole.

Isoniazid preventive therapy is recommended as a health-preserving measure for HIV-infected persons at risk of TB, as well as for those with latent TB infection.

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