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Toxoplasma
gondii - cosmopolitan parasite expressing Iow genetic diyersity
Abstract: T. gondii is
the causative agent of the most common parasitic infections in a
wide variety of vertebrate
hosts, including humans. One third of the human adult population
in the world (between 10
and 85%) depending on geographical location is chronically
infected with this parasite. The life cycle
of T. gondii is
complex, involving mitotic division in intermediate hosts and
meiotic division in definite
hosts (members of cat family) but sexual recombination between
different strains of the parasite
is exceptional in natural population. Strains of T. gondii
can be grouped only into three clonal lineages
(I, II, III), and it is not related to geographical or host
specificity, Recent genetic studies identified
a remarkably limited number of T. gondii
genotypes in nature. In spite of the clonal population
structure, several studies indicate that these three lineages of T. gondii
are not separate species. One
of these lineages (type I) is highly virulent in outbred
laboratory mice, whereas long — term infections are
characteristic for type II and III strains. Type I strains have
been observed in human congenital
and ocular toxoplasmosis, suggesting that this lineage may be more
pathogenic for humans
as well. Increasing frequency of type II found in animal products
is probably strongly related to high
percentage of seropositive patients.
1.
Localization of T. gondii
among the living organisms. 2. Distribution of T. gondii
- the frequency of
infections in a variety of hosts in different regions of the world.
3. Biodiversity of T. gondii
species. 4.
Genetic diversity. 5. Summary |
