the sufferer alternately feels excessively
hot and shiveringly cold.
AIDSAcquired immune deficiency syn-
drome, a deficiency of the immune
systemdue to infection with HIV(human
immunodeficiency virus). In most coun-
tries, illness and death from AIDS is a
growing health problem, and there is,
as yet, no cure or vaccine.
AIDS does not develop in all people
infected with HIV. The interval between
infection and the development of AIDS
is highly variable. Without treatment,
around half of those people infected
will develop AIDS within 8–9 years.
HIV is transmitted in body fluids, in-
cluding semen, blood, vaginal secretions,
and breast milk. The major methods of
transmission are sexual contact (vagi-
nal, anal, or oral), blood to blood (via
transfusions or needle-sharing in drug
users), and mother to fetus. HIV has
also been transmitted through blood
products given to treat haemophilia, arti-
ficial insemination by donated semen,
and kidney transplants; but improved
screening has greatly reduced these
risks. HIV is not spread by everyday con-
tact, such as hugging or sharing crockery.
The virus enters the bloodstream and
infects cells that have a particular recep-
tor, known as the CD4 receptor, on their
surface. These cells include a type of
white blood cell (a CD4 lymphocyte)
responsible for fighting infection and
cells in other tissues such as the brain.
The virus reproduces within the infected
cells, which then die, releasing more
virus particles into the blood. If the
infection is left untreated, the number
of CD4 lymphocytes falls, resulting in
greater susceptibility to certain infec-
tions and some types of cancer.
Some people experience a short-lived
illness similar to infectious mononucle-
osiswhen they are first infected with
HIV. Many individuals have no obvious
symptoms; some have only vague com-
plaints, such as weight loss, fevers,
sweats, or unexplained diarrhoea, des-
cribed as AIDS-related complex.
Minor features of HIV infection in-
clude skin disorders such as seborrhoeic
dermatitis. More severe features include
persistent herpes simplex infections, oral
candidiasis(thrush),shingles, tuberculo-
sis, and shigellosis. HIV may also affect
the brain, causing a variety of neurolog-
ical disorders, including dementia.
Certain conditions, known as AIDS-
defining illnesses, are characteristic of
full-blown AIDS. These include cancers
(Kaposi’s sarcoma and lymphoma of
the brain), and various infections (pneu-
mocystis pneumonia, cytomegalovirus
infection, toxoplasmosis, diarrhoea due
to CRYPTOSPORIDIUMor ISOSPORA, candid-
iasis, disseminated strongyloidiasis, and
cryptococcosis), many of which are
described as opportunistic infections.
Confirmation of HIV infection involves
testing a blood sample for the presence
of antibodies to HIV. Diagnosis of full-
blown AIDS is based on a positive HIV
test along with the presence of an AIDS-
defining illness.
The risk of infection with HIV can be
reduced by practising safer sex. Intra-
venous drug users should not share
needles. There is a small risk to health
workers handling infected blood prod-
ucts or needles, but this risk can be
minimized by safe practices.
Treatment of HIV infection with a com-
bination of antiviral drugs can slow the
disease’s progress, and may prevent
the development of full-blown AIDS. The
2 main types of antiviral drug used are
protease inhibitors, such as indinavir,
and reverse transcriptase inhibitors
such as zidovudine. Treatment is also
available for AIDS-defining illnesses.
AIDS-related complexA combination
of weight loss, fever, and enlarged lymph
nodes in a person who has been infec-
ted with HIV(the AIDSvirus), but does
not have AIDS itself. Many people with
AIDS-related complex will eventually
develop the features of AIDS.
airThe colourless, odourless mixture of
gases that forms the Earth’s atmosphere.
Air consists of 78 per cent nitrogen, 21
per cent oxygen, small quantities of
carbon dioxideand other gases, and
some water vapour.
air conditioningA system that controls
the purity, humidity, and temperature
of the air in a building. Contaminated
air-conditioningsystems may causele-
gionnaires’ diseaseand humidifier feverAIDS AIR CONDITIONING
A