The following is a summary of some of the more common illnesses that people with HIV can get. The list is not comprehensive, and it’s worth remembering that the success of anti-HIV treatment means that many of the illness listed below are now very rarely seen in people with HIV in this country.

However, the PCP and tuberculosis both affect about 200 people a year in the UK. Cases of these illnesses often occur in people who are unaware that they are HIV-positive and are only diagnosed with HIV because they are so unwell with these infections.

Treatments are constantly improving, so only very basic information about treatments has been included. More comprehensive information can be found on NAM’s website www.aidsmap.com.

Most illnesses are caused by one of the following:

• A virus. These are simple organisms which reproduce using the building blocks of your own cells. This makes it very hard to get rid of them.

• Bacteria. These are single-cell organisms that antibiotics can kill.

• Protozoa and parasites. These are more complex organisms.

• Fungi. Yeasts and organic growths.

• Cancer. Cancers develop when your own cells develop out of control.

It’s possible that you have already been infected with the organisms which cause many of the illnesses listed in this section. This is because they are very common across the population and only cause problems if the immune system is damaged and unable to keep them in control. Even then, there are sometimes effective treatments to stop the illnesses flaring up (preventative treatment or prophylaxis). And taking anti-HIV treatment normally means that the immune system gets strong enough to prevent HIV-related illnesses happening in the first place or coming back again if you experience one.

Candidiasis (thrush)

This is a fungus that can affect wet and warm surfaces, such as the mouth, throat, vagina, anus and top of the penis. It looks a bit like cottage cheese and can be painful. Treatments vary depending on its severity, and are effective. You can get thrush when you have quite a high CD4 cell count.

CMV (cytomegalovirus)

Cytomegalovirus (CMV) means 'great cell virus.' It can affect the eyes, gut, lungs and nervous system. Many people are infected with CMV, but it doesn't cause any problems so long as they have a reasonably strong immune system. Illness caused by CMV is now very rarely seen in people with HIV in this country because of the effectiveness of anti-HIV treatment.

When CMV does become a problem, it tends to be in people with very low CD4 cell counts (below 50). If not treated early, it can cause very serious problems such as blindness.

One of the best treatments for people with, or at risk of CMV, if anti-HIV therapy as this will strengthen the immune system so it is able to fight the infection.

There are also specific treatments and an effective oral treatment recently became available. People at risk of CMV are often given low doses of this drug to prevent the infection causing problems.

Cryptococcal meningitis

Cryptococcus is a fungus found in bird excrement. In humans, it usually infects the lungs, causing a chest infection, but can rapidly infect the meninges (the lining of the brain) causing fever, headache, stiff neck and confusion. A lumbar puncture is needed to properly diagnose it. Meningitis occurs in people with very advanced HIV disease.

Different treatments are used depending on the severity of the infection, and in very severe cases these drugs can have quite severe side-effects. After recovering from meningitis, it is important to take prophylactic treatment to stop it coming back.

Cryptosporidiosis

Cryptosporidiosis, normally abbreviated to just crypto, is caused by a parasite that gets into the gut. It is normally transmitted in the water supply, or by contact with human or animal excrement. It causes watery diarrhoea, which can lead to very rapid weight loss. It can also infect the liver, causing inflammation.

Crypto often clears up by itself after a few weeks in people with less damaged immune systems. Although many drugs can be used to treat it, none are completely effective. Anti-diarrhoea and rehydration treatments are important in limiting the severity of the illness. It is also wise to see a dietitian if you get crypto, to make sure that you are getting enough nutrients from your diet.

HIV encephalopathy

This disease, sometimes called AIDS dementia complex or HIV-associated dementia, is caused by HIV’s direct effects on the central nervous system. The first symptoms consist of minor changes in behaviour, coordination and concentration. Sometimes, those affected become apathetic or withdrawn. In some cases, it becomes much worse, resulting in a loss of control of movement, schizophrenia and suicidal impulses.

Many other illnesses can cause nervous or mental health problems, and HIV-associated dementia is very rare. However, it can occur in people who have very low CD4 cell counts.

The only effective treatment is anti-HIV therapy, and the success of anti-HIV treatments is the main reason why HIV-associated dementia is now so rare.

Kaposi’s sarcoma (KS)

KS is a cancer which occurs most commonly on the skin, but can also affect the organs and intestines. It is thought to be caused by a type of herpes virus that is sexually transmitted. Most cases of KS in this country have been seen in gay men, although an increasing number of cases have been seen in people who have come to the UK from Africa.

KS looks like purple, brown or black marks on the skin. These can look like bruises, bites or other infections, so a biopsy of the affected area is needed to confirm KS.

KS normally develops when you have a low CD4 cell count. The best way of treating it is to boost the immune system. Anti-HIV treatment regimens based on either protease inhibitors or non-nucleoside reverse transcriptase inhibitors (NNRTIs) have been shown to be equally effective at getting rid of KS. Individual lesions on the skin can be frozen off, and KS affecting the internal organs or intestines can be treated with chemotherapy or radiotherapy.

In 2007 doctors in San Francisco reported a cluster of cases of KS in older gay men who were all doing well on anti-HIV treatment. Unlike the KS seem in the days before HIV treatment became available, the KS in these patients wasn't dangerous. KS is caused by a herpes virus - HHV8 and doctors in San Francisco think that low-grade and  long-term suppression of the immune system allowed an 'indolent' form of KS, like that seen in older HIV-negative patients, to develop.

Lymphoma

This is cancer of the lymphatic system: the body’s internal drainage system. It is normally seen in the lymph nodes, which swell up, but it can spread throughout the body. Symptoms include night sweats and fevers, but remember that many infections can cause these symptoms, as well as swelling of the lymph nodes.

Lymphoma has become a lot less common since effective anti-HIV treatment became available, and when it does develop, it can often be successfully treated by staying on HIV drugs and by courses of  chemotherapy or radiotherapy.

MAI

This is caused by a bacteria similar to tuberculosis. It can be caught from soil or tap water. It only affects people with very severely damaged immune systems, when it can cause weight loss, fever and diarrhoea. If you have a very low CD4 cell count, your doctor might recommend that you take preventative treatment to stop you getting MAI. There are a number of treatments against MAI, but their success varies. As with many AIDS-defining illnesses, the best treatment is often to strengthen the immune system using anti-HIV treatments.

PCP (pneumocystis pneumonia)

PCP and tuberculosis are the two most common AIDS-defining illness in the UK. PCP affects about 200 people every year. Most of these cases are seen in people who did not know that they had HIV until they become unwell with PCP. Thanks to HIV treatment, PCP is now a very rare infection in other HIV-positive patients.

PCP is a fungus that lives in the lungs and causes inflammation in a person who has a damaged immune system. PCP can be a very dangerous infection if not treated early, so you should always tell your doctor if you have a persistent dry cough and shortness of breath. Other symptoms include fever and night sweats.

There are highly effective treatments against PCP, the most common being co-trimoxazole, but this can cause an allergic reaction. To avoid this, your doctor may desensitise you to the drug by giving you a progressively larger dose each day, over a number of days.

PCP rarely develops in people whose CD4 cell counts are above 200, the point at which you should start taking anti-HIV treatment. If your CD4 cell count is below or around 200 you should take small doses of special antibiotics every day to stop you getting PCP. This is called PCP prophylaxis, and youneed to take it if you have a low CD4 cell count even if you are taking anti-HIV treatments, until your immune system strenghtens. PCP prophylaxis also protects against toxoplasmosis (see below).

Thrombocytopenia

This means that you have a low number of platelets in your blood – small cells that help your blood to clot. It can cause bruising and, in serious cases, internal bleeding.

As it is often caused by HIV itself, the most effective treatment is HIV therapy. It is very important not to take anti-inflammatory drugs such as ibuprofen, as they can make the condition worse and cause internal bleeding.

Toxoplasmosis

Toxoplasmosis, or ‘toxo’ for short, is caused by a parasite transmitted in raw or undercooked meat. Cat droppings are also a theoretical risk.

Toxo can cause cysts to form on the brain, leading to headaches, fever, drowsiness, and fits. Without treatment, these can become very severe and lead to coma.

This disease is now very rarely seen in people with HIV, thanks mainly to potent anti-HIV treatment. It only develops in people with weak immune systems, so if you are at risk of toxo you should be taking anti-HIV treatment. But cases of toxo were falling even before effective anti-HIV therapy became available. This is because the drug used to treated PCP, co-trimoxazole (Septrin), is also effective against toxo, and people who take small doses of co-trimoxazole to protect them from PCP will also be protected against toxo.

Tuberculosis (TB)

TB and PCP are the two most common AIDS-defining illness seen in the UK, with around 200 cases of TB diagnosed in HIV-positive individuals each year. Worldwide, TB is the leading cause of illness and death in people with HIV.

TB is caused by a very small bacterium. It is a very serious infection and causes fever, coughing, chest pain and weight loss. Unlike nearly every other AIDS-defining illness, you can become ill with TB even when you have a relatively high CD4 cell count.

TB is treated with a combination of antibiotics, which are normally taken for six months. These have to be taken very rigorously, or you run the risk of developing multi-drug-resistant TB.

For more information on TB, you can read the free NAM booklet HIV and TB, which is available from HIV clinics or can be downloaded from www.aidsmap.com.