Toxoplasma gondii infection in sheep and cattle.

Toxoplasma gondii is a protozoan parasite that can infect all warm-blooded animals. Sheep and cattle show different susceptibilities to T. gondii infection. Primary infection in pregnant sheep can result in abortion or the birth of weak lambs but they are then protected against further challenge by the development of an effective immunity. Cattle on the other hand can be readily infected, but abortion or perinatal mortality have not been recorded. The evidence suggests that cattle develop a more effective immune response to T. gondii infection than sheep. Potential mechanisms to explain these differences are discussed in this paper.