Epidemiology of Neosporosis

Cattle are infected with N. caninum by exogenous (horizontal or postnatal) transmission or by endogenous (vertical or prenatal).

Exogenous transmission

Exogenous transmission occurs through the ingestion of feed or water contaminated with N. caninum oocysts shed with the faeces of the definitive canine host.

Cows that eat food contaminated by infected dog faeces ingest N. caninum oocysts.

Endogenous transmission

During pregnancy N. caninum is released from tissue cysts of cows or heifers that are already infected with the parasite. The tachyzoites are transmitted across the placenta from the dam to the fetus.

The rate of endogenous transmission is very high being estimated to be of around 95%. Transmission rate seems to decrease with age.

Due to endogenous transmission calves are born infected with the parasite. Heifers kept as replacements contribute to the maintenance of the disease in the herd.

Endogenous transmission appears to be the predominant route of infection in cattle. However exogenous transmission can take place wherever there is a definitive host present.

Neosporosis life cycle

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Are bulls able to transmit Neosporosis?

The role of the bull in the transmission of N. caninum is still under investigation. Although the parasite has been identified in semen samples from sero-positive bulls, it has not been demonstrated yet that venereal transmission takes place and what would be the importance of this route in field conditions.

Effect of N. caninum infection on the fetus

In endogenous and exogenous transmission the outcome of Neospora infection will depend on the stage of gestation.
Read more in Immunology.