Speculation on possible life cycles for the clonal lineages in the genus Toxoplasma

Recent evidence suggests that the strains currently classified in the genus Toxoplasma, ie. within the species Toxoplasma gondii, may actually comprise at least two clonal lineages correlated with their virulence in mice. Here, Alan Johnson reviews these data in the context of evolution and speciation within the genus, and raises hypostheses on how the virulent lineage may undergo an asexual life cycle in nature, similar to that found for the very closely related coccidian, Neospora caninum. The putative vertical transmission life cycle of this mouse virulent lineage of T. gondii could involve passage to the foetus late in pregnancy, or transmission in milk to the neonate after birth.