Toxoplasma gondii
The protozoan parasite Toxoplasma gondii has been associated
with cats as the main source of infection to humans for many
years. Recent evidence suggests that a high prevalence rate in
pigs infers that raw or undercooked meat is a significant
source of infection. In many countries, the human population
is infected at a rate of 4 0 % or more. Toxoplasma poses a
significant public health risk to pregnant women (being a
cause of birth defects in congenitally infected foetuses) and to
immunodepressed or immunocompromised individuals,
both resulting from acute or chronic/latent infections. The
life-cycle and transmission patterns of T. gondii are given in
Figure 5. Sporulation in the environment takes at least
24 hours, depending on temperature, and is necessary for
oocysts to become infective for the next host (Fig. 5).
Transplacental transmission is an important mode of infection
in humans, pigs, sheep and goats.
Epidemiology
Human infection with T. gondii is relatively high compared to
most other diseases. Serological surveys, summarised by
Dubey and Beattie (10) report rates of up to 100% of the
population infected in many countries where testing had been
conducted. In the USA, surveys suggest that approximately
30% of the general population is infected or has been exposed
to infection (8), while prevalence in a younger population