The pathology associated with acute, chronic, and recrudescent Babesia gibsoni infections was characterized in a group of 6 naturally or experimentally infected, spleen-intact and splenectomized dogs. All experimentally infected dogs became acutely parasitemic, lethargic, anemic, thrombocytopenic, and hemoglobinuric. Anatomic lesions associated, with the disease included diffuse nonsuppurative periportal and centrilobular hepatitis, multifocal necrotizing arteritis, membranoproliferative glomerulonephritis, reactive lymphadenopathy, diffuse erythrophagocytosis, and extramedullary hematopoiesis. The density of CD3+ lymphocytes within the liver sinusoids was markedly increased. Aggregates of large mononuclear cells with immunohistochemical features of activated macrophages were demonstrated in the central veins of the liver. Kupffer cells throughout the hepatic sinusoids appeared hypertrophic and prominent. The density of sinusoidal T lymphocytes, macrophages in central veins, and the degree of Kupffer cell hypertrophy were greatest in the splenectomized dogs. Multifocal deposits of IgM antibody were immunohistochemically demonstrated within the walls of inflamed arteries and renal glomeruli. The results of this study suggest that intense immunostimulation resulting in activation and expansion of T and B lymphocyte populations, macrophage recruitment and activation, vasculitis, glomerulonephritis and anemia contribute to the pathology associated with B. gibsoni infections.

ABSTRACT. Prevalence of antibody to Neospora caninum (NC) in Japanese dogs were examined. The antibody was positive in 15 of 48 dogs (31.3%) reared in the dairy farms that had case of the abortions due to NC infection or had the cattle seropositive to NC, whereas the prevalence was 7.1% (14 of 198 dogs) among the dogs kept in urban areas. In one dog breeder, all 17 Shetland sheepdogs older than 7 months were seropositive, and one pup was diagnosed as neosporosis 2 months before the first serological examination. The antibody titers of the dogs kept at this breeder were almost unchanged for 1.5 years. Serological evidence of the dogs in the dairy farms and urban areas indicates the transmission of NC between dogs and cattle. Also serological results of the dogs in one breeder may suggest the potential horizontal transmission among dogs. -KEY WORDS: canine, Neospora, seroprevalence.

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ABSTRACT. Primary culture of bovine brain cells was examined for its susceptibility to Neospora caninum infections, and this model was used to investigate the effects of bovine interferon gamma (IFN-γ) and tumor necrosis factors alpha (TNF-α) on tachyzoite growth. Tachyzoites of N. caninum grew well in this culture, and tachyzoite growth in astroglia and microglia were confirmed by immunocytochemical staining. IFN-γ inhibited the tachyzoite growth, and this inhibition was not reversed by the addition of nitric oxide antagonist. TNF-α, to a lesser extent, also inhibited the tachyzoite growth. Th-1 type cytokines may play an important role in host defense mechanisms in N. caninum infection.-KEY WORDS: brain culture, cytokine, Neospora caninum.

Neospora caninum is a protozoan parasite that causes bovine abortion. The epidemiology of N. caninum is poorly understood and little is known about the genetic diversity of the parasite, or whether individual isolates differ in virulence. Such diversity may, among other factors, underlie the range of pathologies seen in cattle. In this study we analysed biological and genetic variation in 6 isolates of N. caninum originating from canine and bovine hosts by measurement of growth rate in vitro, Western blotting and random amplification of polymorphic DNA (RAPD). This comparative analysis of intra-species diversity demonstrated that heterogeneity exists within the species. The relative growth rate in vitro, as assessed by 3[H]uracil uptake, showed significant variation between isolates. However, no significant differences were detected between the antigenic profiles of each isolate by Western blotting. RAPD-PCR was performed on DNA from the 6 Neospora isolates; 3 strains of Toxoplasma gondii, Sarcocystis sp. and Cryptosporidium parvum were also analysed. Twenty-six RAPD primers gave rise to 434 markers of which 222 were conserved between all the Neospora isolates and distinguished them from the other Apicomplexa. An additional 54 markers were unique for Neospora but were polymorphic within the species and able to differentiate between the individual isolates. The RAPD data were subjected to pair-wise similarity and cluster analysis and showed that the Neospora isolates clustered together as a group, with T. gondii as their nearest neighbour. N. caninum isolates showed no clustering with respect either to host or geographical origin. The genetic similarity between Neospora isolates from cattle and dogs suggests that these hosts may be epidemiologically related, although further analysis of bovine and canine field samples are required. The genetic and biological diversity observed in this study may have important implications for our understanding of the pathology and epidemiology of neosporosis.

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