Is there more than one species in the genus Toxoplasma??

A complete life cycle for the ubiquitous protozoan parasite Toxoplasma was proposed over 25 years ago. Since that time, despite attempts to make the genus polyspecific, there has been only one species, Toxoplasma gondii, consistently recognised in the genus. Recent studies on taxa in genera closely related to Toxoplasma such as Neospora, Hammondia, Frenkelia, Isospora and Sarcocystis, have convincingly showed the need for a reclassification of many of the species in these genera. However, in addition to these genus level studies, over the last 10 years several laboratories have used molecular techniques including isoenzyme electrophoresis, restriction fragment length polymorphism analyses, random amplified polymorphic DNA - polymerase chain reaction, and comparisons of the small subunit ribosomal RNA gene, DNA polymerase alpha intron, and 70 kDa heat shock protein gene nucleotide sequences to investigate the genetic diversity among strains in the species T. gondii. Overall, the results of these analyses confirm that the strains in the genus Toxoplasma comprise a limited number of clonal lineages, directly correlated with their virulence in mice. The aim of this presentation is to review the molecular research in this area in order to raise the hypothesis that there may be more than one species in the genus Toxoplasma, which may contain taxa with distinct and different life cycles.