ABSTRACT
In 1998, a new species of Neospora, N. hughesi was described from a horse in California, USA. To date, N. hughesi has been reported only from horses. Therefore, available information on N. hughesi and neosporosis in horses is summarized. Antigenic and molecular differences between N. hughesi and N. caninum have been reported. There is a 6%–9% difference in the amino acid sequences of 2 surface antigens (SAG1 and SRS2) between these 2 species. Rodents are more susceptible to experimental infections with N. caninum than N. hughesi. Necrosis of the myocardium, even visible macroscopically, was the predominant feature of N. hughesi infection whereas lesions in liver, lungs, and brain predominated in N. caninum infections. In most of these surveys N. caninum tachyzoites were used as antigens. Confirmed fatal neosporosis has been reported in very young or old horses. The earliest reported case was a late-term fetus.
