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FOOD2160/2165: Nutrition and AIDS

Dr JA Illingworth

Incidence of HIV infection:

World Health Organisation figures for 2006 suggest that about 39.5 million people world-wide are currently infected with human immunodeficiency virus (HIV), including 2.3 million children. [Click here to download the full report (5MB).] There were 4.3 million new cases, and 2.9 million people died. Acquired Immunodeficiency Syndrome (AIDS) has killed more than 25 million people since it was first recognized in 1981, making it one of the most destructive epidemics in recorded history.

Infection rates are highest in southern Africa with 20% to 30% of pregnant women infected in Botswana, Lesotho, Namibia, South Africa, Swaziland and Zimbabwe, and about 26 million victims overall. Infection rates are rising in Asia and the Far East. Most people are infected through heterosexual contacts. Some progress has been made in East Africa, with a reduced incidence after safe sex campaigns.

See also the AVERT website for many additional details. The AVERT website is excellent, packed with useful, accurate information.

Clinical features of HIV and AIDS:

HIV is an RNA retrovirus which infects CD4+ T-helper cells, which normally regulate the immune system. A DNA copy of the infective viral RNA is inserted into the host cell genome, where it generates further RNA copies that infect other cells. Copying by reverse transcriptase is prone to errors, leading to a high mutation rate and appearance of drug resistant clones.

Viral load peaks 2-3 weeks after infection. This is often asymptomatic but may be associated with a mild illness that spontaneously resolves. Antibodies are produced against viral coat proteins but these cannot eliminate the infection. Viral numbers fall and the disease enters a latent phase which may last for ten years, during which time the patient remains infective.

The immune response to HIV

Figure 2.46 reproduced from Kumar & Clarke

Eventually viral numbers rise again, CD4+ lymphocytes fall to very low levels and the patient shows gradually worsening symptoms of AIDS, typically over a 12-year period. Treatment at this stage with anti-retroviral drugs may induce dramatic remissions, but the high mutability of the virus makes it likely that drug resistant strains will ultimately appear.

See also: Kumar & Clarke (2005) Clinical Medicine 6th ed. pp 129-151 Elsevier ISBN 0702027642 or download a detailed specialist account for the HAART website.

Opportunistic infections:

AIDS patients typically suffer from a variety of opportunistic infections that reflect their weakened immune system. These may result from reactivation of latent infections which are contained in healthy individuals. High-grade pathogens such as Mycobacterium tuberculosis, Candida albicans and herpesviruses appear first, followed by less virulent organisms such as Cryptosporidium and Pneumocystis carinii. The lack of a functioning immune system makes these infections difficult to treat.

Other symptoms:

Cachexia

This Greek word means "poor condition" and is normally applied to the severe weight loss associated with serious diseases such as major burns, heart failure, cancer and AIDS, which was first known in Africa as "slim disease".

The key mediators are the pro-inflammatory cytokines such as TNF-α These are protein messengers produced by various immune cells, including macrophages, natural killer cells, T cells, B cells and mast cells. These signals normally help to recruit other immune cells to a focus of infection, but over-production may be life-threatening.

Cachexia is a hypermetabolic state, associated with elevated temperature, weight loss, protein degradation (i.e. muscle wasting) fat breakdown, hyperglycaemia, anorexia and approaching death.

Recent reviews:

Cytokines and the Immune System:

There are dozens of cytokine messengers involved in regulating the immune system. The CD4 cells play a key role in recognising processed antigen displayed by antigen presenting cells on class II MHC proteins, and in controlling the balance between cell-mediated inflammatory responses involving T cells and the production of circulating antibody molecules by B cells.

Textbooks

Click here for more details of the immune system.

Anti-retroviral therapies:

Several classes of anti-retroviral drugs are now available for high activity anti-retroviral therapy (HAART) which can produce a 12-fold reduction in AIDS symptoms. These include:

Many of these drugs are expensive and have serious side effects. In particular, NRTIs also inhibit the mitochondrial DNA polymerase as well as reverse transcriptase, leading to lactic acidosis. Mitochondrial damage may also contribute to the lipodystrophy (abnormal fat distribution with cardiovascular complications) observed in many patients taking NRTIs. The virus may also acquire resistance. New or improved anti-retroviral drugs are still being developed.

Textbooks

Malnutrition:

There are two aspects to this. All AIDS patients with cachexia / anorexia have inadequate food intake, but in poor countries lack of money compounds this problem, and may be associated with specific dietary deficiency states.

Dietary Advice:

In general, dietary advice to patients suffering from AIDS is similar to advice given to the general population, except that target food consumption is increased by about 30% to combat AIDS-related weight loss. All patients must be treated as individuals. Although the majority of patients have lost weight, a minority may still be clinically obese, and will require a weight-reducing diet.

Regulation of Body Weight

I give a lecture on "Regulation of Body Weight" to the first year medical students. This is mainly written in relation to obesity, when clearly for AIDS patients we have entirely the opposite problem, but the regulatory mechanisms are still the same. I hope it might be helpful.

If you have comments, queries or suggestions, email me at J.A.Illingworth@leeds.ac.uk. You can also contact me via Leeds City Council.