Toxoplasmosis
is a common infection with the germ Toxoplasma
gondii. This germ is often acquired before
birth, but is sometimes passed on by domestic
cats or acquired by eating undercooked meat
from infected animals. The germ infects
all known mammals and most of us already
have antibodies to it.
Toxoplasmosis
can affect the nervous system and especially
the eye. It is a common cause of permanent
damage to the retina, causing a blind spot
of variable size, which may enlarge at intervals
throughout life. The condition should not
be confused with toxocariasis, which is
a parasitic worm infestation, also capable
of affecting the eye.
When heavy
infection occurs before birth, the foetus,
which has little immunological protection,
often suffers extensive damage to the nervous
system and elsewhere, and miscarriage or
stillbirth is common.
For the same
reasons, toxoplasmosis may be a severe disorder
in people with immune deficiency, either
from HIV/AIDS or from another cause, with
tissue destruction in the brain, lungs and
heart caused by the rapidly spreading organisms.
About ten per cent of patients with AIDS
suffer severe encephalitis (brain inflammation)
from toxoplasmosis.
Symptoms
In most cases,
the infection causes no symptoms or observable
effects, as the immune system is capable
of controlling it and preventing significant
damage. Antibodies, however, operate less
efficiently in the internal tissues of the
eye than elsewhere, and damage to the retina
and the underlying layer (the choroid) is
fairly common.
The condition
tends to recur, each time causing further
permanent damage to the retina. But it is
only when the central (macular) part of
the retina is involved that loss of vision
is apparent to the affected person.
Apart from
eye damage, Toxoplasma infection sometimes
causes widespread enlargement of the lymph
nodes in people with apparently normal immunity.
The node enlargement may be accompanied
by fever, headache, a feeling of sickness,
muscle and joint aches, and liver enlargement.
Diagnosis
Toxoplasmosis
of the eye is diagnosed by an examination
of the retina with an instrument called
an ophthalmoscope. The retinal damage is
easily seen and is characteristic of the
condition.
Treatment
Usually no
treatment is necessary and a full recovery
is made.
People with
a reduced immune system and pregnant women
may be given antibiotics or antimalarial
drugs such as pyrimethamine.
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Toxoplasmosis
