Infections

AIDS

AIDS stands for the Acquired Immune Deficiency Syndrome. It is caused by HIV (Human Immunodeficiency Virus), and a person who is HIV positive is said to have AIDS if they develop an "AIDS defining illness".

In the presence of HIV infection there will be a decline in the functioning of a person's cellular and humoral (antibody related) immune system over a period of time. From a practical level the degree of immune system compromise is measured as the "CD4 count"- a measure of the number of a particular type of white blood cell. Patients who are HIV positive also have their "Viral Load" measured and this quantifies the number of virus particles in a millilitre of plasma.

The Centres for Disease Control in the USA has devised a system of classification of the extent of HIV infection based on a person's CD4 count and the presence or absence of HIV related symptoms or the AIDS defining illnesses. In the past few years it has become arguable as to how useful this classification is. This is especially the case now that there are anti-HIV drugs available that boost the immune system (raise the CD4 count) and greatly affect a patient's symptoms and likelihood of developing an AIDS defining illness.

The AIDS related complex (ARC) describes a collection of symptoms such as fever, night sweats, weight loss, oral thrush, shingles and fungal skin infections that are often present in HIV positive patients prior to developing AIDS.

Approximately 75% of HIV positive patients develop AIDS within 9-10 years of becoming HIV positive. The aim in the future is that by more widespread HIV testing and surveillance patients will be able to start on anti-HIV drugs (antiretrovirals) prior to the development of AIDS. Certain HIV positive patients claim to be perfectly fit and healthy many years after the initial acquisition of the virus. This group of people form what is known as the "long-term non-progressors". It is not fully clear what makes some patients with HIV deteriorate more quickly than others.

Most of the AIDS defining illnesses have specific treatments that are applicable to them. Some of these treatments can be modified and used as "prophylaxis". This means prevention and can either be used in a primary or secondary setting. This would depend on whether or not a patient has already experienced a particular AIDS defining illness, or whether they are susceptible to one because of a declining CD4 count.


The commonest AIDS defining illnesses are as follows:

Pneumocystis Carinii Pneumonia (PCP)

This is a very severe and potentially fatal pneumonia, which is characterised by profound hypoxia or low oxygen levels. Although treatable with antibiotics, there are serious complications including pneumothoraces or collapsed lungs and respiratory failure requiring transfer to an Intensive Care Unit for artificial ventilation.

Tuberculosis

TB is caused by the organism Mycobacterium Tuberculosis and is very common in African patients. It can affect the lungs but also several other organs including the gut, brain, kidneys and bone marrow. There are several other mycobacteria in the same family as MTB including mycobacterium avium intracellulare (MAI) and mycobacterium kansasii, which can cause infection both in the lungs and sometimes the bone marrow.

One important aspect of TB infection is that treatment MUST include three if not four antibiotics which must be continued for prolonged periods of at least six to nine months if eradication of the infection is to be successful. Discontinuation of treatment early is a leading cause of antibiotic resistance and this can have disastrous consequences and can lead to untreatable cases of "multi-drug resistant TB".

Cerebral Toxoplasmosis

This infection is characterised by the development of mass lesions in the brain, which can give rise to a wide range of neurological symptoms including fits. It is usually diagnosed by performing a CT scan of the brain. Most patients with HIV who develop severe neurological symptoms such as sudden headaches, fits or visual loss will undergo this investigation.

Cytomegalovirus Retinitis

Cytomegalovirus (CMV) is from the Herpes family of viruses and can cause severe scarring of the retinae or backs of the eyes in HIV positive patients. This can lead to visual loss if untreated. It usually only affects patients with very low CD4 counts. The aim is to try and prevent people from developing this by starting them on antiretroviral drugs before the CD4 count becomes too low. In those who have already suffered an episode of CMV retinitis they must continue taking prophylactic Ganciclovir until their CD4 count rises appreciably. CMV can also affect any section of the gut causing severe ulceration.

Cryptosporidial Diarrhoea

This is a parasitic infection resulting in prolonged diarrhoea that is very difficult to control. Unfortunately, earlier attempts to eradicate the parasite with specific drugs proved futile. The mainstay of treatment for this condition includes the usage of loperamide and codeine to slow down bowel movements and antiretroviral therapy to raise the CD4 count. Patients are often advised to drink only filtered or boiled water if their CD4 counts are very low in order to try and avoid infection with this microorganism.

Cryptococcal Meningitis

This is a fungal meningitis and has the same symptoms as a bacterial meningitis namely severe headaches, fevers, and ultimately drowsiness, fits and coma. It requires a lumbar puncture to remove a sample of spinal fluid in order to be diagnosed and can usually be treated well with antifungal drugs. Although effective it must be remembered that these drugs like all others have side effects and can be unpleasant to take.

Kaposi's Sarcoma

This is a type of malignant tumour or cancer that affects predominantly homosexual men and Africans with HIV. It is thought to be related to a type of Herpes Virus known as human herpes virus 8 but the exact relationship is unclear. It causes lesions or spots and lumps on the skin and in the lungs, gut and lymph nodes. Skin lesions do not necessarily need treatment with radiotherapy unless they are particularly cosmetically disfiguring.

Other tumours such as Non-Hodgkin's Lymphoma and Primary Cerebral Lymphoma are common in HIV infection and classified as AIDS defining illnesses.

All of these conditions tend to improve and the risk of developing them decreases if effective antiretroviral therapy is taken. Please go to our link on the website to read more about this.

From the point of view of preventing the spread of HIV and AIDS there are several key factors. The practice of safer sex is probably the most important factor in the UK . This includes not only using condoms but also a reduction in the number of sexual partners and minimization of sexual practices that are considered particularly dangerous i.e. unprotected anal sex.

Injecting drug users are encouraged to not share equipment and needle exchange schemes are running in most major cities.

Screening of pregnant women and offering antiretroviral drugs at the time of delivery as well as consideration of planned Caesarean section for these women aims to reduce maternal transfer of the virus to offspring.

Vaginal microbicides or "chemical condoms" are currently being extensively researched and these two latter strategies are hoped to be particularly effective at reducing the spread of HIV in Africa . However, an effective microbicide has yet to be developed.

At present there is much research going on into vaccines against HIV. Currently there are in excess of 30 clinical trials of both preventative and therapeutic HIV vaccines which are underway around the world. At the moment, though, any prospect of an effective vaccine seems years away.