Neospora hughesi: experimental infections in mice, gerbils, and dogs

Neospora hughesi is a recently described cause of equine protozoal myeloenc ephalitis (EPM). A rodent model for pathogenicity would facilitate developm ent of therapies to be used in horses. In the present study, we examined th e susceptibility of BALB/c gamma-interferon gene knockout (gamma-INFKO), BA LB/c, CD-1, and C57BL/6 strains of mice and gerbils to infection with tachy zoites of the Nh-A1 strain of N. hughesi isolated from a horse from AL, USA . Only the gamma-IFNKO mice developed severe clinical disease following inf ection with N. hughesi and died 19-25 days after infection and exhibited se vere cardiac lesions. In contrast, experimental infection of gamma-INFKO mi ce with tachyzoites of the NC-1 or NC-Liverpool strains of Neospora caninum resulted in deaths 8-10 days after infection. The most severe lesions were in the livers, spleens, and lungs of these mice. Gerbils inoculated with N . hughesi did not develop clinical disease, had few microscopic lesions, bu t did seroconvert. Two dogs fed the brains of mice, shown to contain N, hug hesi tissue stages by cell culture and gamma-IFNKO mouse bioassay, did not shed N, caninum-like oocysts over a 23 days observation period. The marked difference in pathogenicity between the two species of Neospora in gamma-IF NKO mice, and lack of oocyst excretion by dogs fed N, hughesi infected mice provide additional evidence that the species distinction between N. caninu m and N. hughesi is valid. (C) 2000 Elsevier Science B.V. All rights reserv ed.