Neospora Caninum - Life Cycle and Transmission

Life Cycle and Transmission

Neospora caninum has a heteroxenous life cycle, with the sexually reproductive stage occurring in the intestine of a definitive host. Until recently, the only known definitive host was the domestic dog. New research has determined that coyotes (Canis latrans), gray wolves (Canis lupus), and Australian dingos (Canis lupus dingo) are also definitive hosts. Oocysts passed in the feces of the definitive host are ingested by an intermediate host, such as cattle. These become permanently infected, and form tissue cysts. Pregnancy activates these cysts, and active infection often causes spontaneous abortion. If the aborted foetus and membranes are then eaten by the definitive host, they cause further infection and the cycle is complete. Transplacental transmission (passage from mother to offspring during pregnancy) has also been shown to occur in dogs, cats, sheep and cattle. Other carnivores, for example the red fox (Vulpes vulpes), may also be intermediate hosts, but they are not known to be definitive hosts. Neospora caninum does not appear to be infectious to humans. In dogs, Neospora caninum can cause neurological signs, especially in congenitally infected puppies, where it can form cysts in the central nervous system.

The discovery that coyotes are definitive hosts may increase the risk of transmission of N. caninum to domestic livestock as well as to wild ruminants such as white tailed deer (Odocoileus virginianus). Coyote range now includes most of North and Central America. Studies suggest that the parasite may be widespread among wildlife and that infection cycles cross over between wild and domestic animals.

Recent studies have broadened the list of known intermediate hosts to include birds. N. caninum has recently been found to infect domestic chickens and house sparrows (Passer domesticus) which may become infected after ingesting parasite oocysts from the soil. Sparrows, which are common in urban and rural areas, may serve as a food source for wild and domestic carnivores. N. caninum has also been detected in common buzzards (Buteo buteo) and magpies. The presence of birds in cattle pastures has been correlated to higher infection rates in cattle. Birds may be an important link in the transmission of N. caninum to other animals.