Recent studies found that isolates of Toxoplasma gondii from Brazil were biologically
and genetically different from those in North America and Europe. However, to date
only a small number of isolates have been analysed from different animal hosts in
Brazil. In the present study DNA samples of 46 T. gondii isolates from cats in 11
counties in São Paulo state, Brazil were genetically characterised using 10 PCR restriction
fragment length polymorphism markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8,
c29-2, L358, PK1 and Apico. An additional marker, CS3, that locates on chromosome
VIIa and has previously been shown to be linked to acute virulence of T. gondii was
also used to determine its association to virulence in mice. Genotyping of these 46
isolates revealed a high genetic diversity with 20 genotypes but no clonal Type I,
II or III lineage was found. Two of the 46 isolates showed mixed infections. Combining
genotyping data in this study with recent reported results from chickens, dogs and
cats in Brazil (total 125 isolates) identified 48 genotypes and 26 of these genotypes
had single isolates. Four of the 48 genotypes with multiple isolates identified from
different hosts and locations are considered the common clonal lineages in Brazil.
These lineages are designated as Types BrI, BrII, BrIII and BrIV. These results indicate
that the T. gondii population in Brazil is highly diverse with a few successful clonal
lineages expanded into wide geographical areas. In contrast to North America and Europe,
where the Type II clonal lineage is overwhelmingly predominant, no Type II strain
was identified from the 125 Brazil isolates. Analysis of mortality rates in infected
mice indicates that Type BrI is highly virulent, Type BrIII is non-virulent, whilst
Type BrII and BrIV lineages are intermediately virulent. In addition, allele types
at the CS3 locus are strongly linked to mouse-virulence of the parasite. Thus, T.
gondii has an epidemic population structure in Brazil and the major lineages have
different biological traits.