Isolation, Identification, and Pathogenicity of Neospora caninum China Yanbian strain.

Background: The aim of the study was to provide a point of reference to study the Neospora caninum infections in China.

Methods: Genome DNA was extracted from the brains of aborted fetuses and specific PCR was performed with N. caninum Nc5-targeted specific primers. Fetal bovine brain tissues were homogenized and continuously cultured in Vero cells with double antibodies. The medium was replaced at 2-d intervals and the state of cells was observed.

Results: A 608 bp Nc5 gene band was detected by PCR amplification. After sequencing, the sequence of the sample shared 99.5% homology with GenBank (AF061249). Brain homogenates were continuously cultured in Vero cells for 34 d and N. caninum was found. The results of IFAT and Nc5 gene-based PCR detection were N. caninum-positive, and the parasite was tentatively named N. caninum China Yanbian strain. BABL/c mice were inoculated with the separated parasites and showed clinical symptoms of ataxia and limb paralysis after 12 d. Only 3 mice survived. The blood of dying mice and the hearts, livers, spleens, lungs, kidneys, and brains of dead mice were collected aseptically. The Nc5 gene-based PCR showed that N. caninum may exist in brains, livers, and spleen. Based on immunohistochemical observations, we showed that N. caninum tachyzoites existed in the brains and livers.

Conclusion: We have successfully isolated bovine-specific N. caninum strain from brain tissues of aborted cattle in the China Yanbian region. This isolated strain has a strong infectious ability towards BABL/c mice.