Isolation and pathogenicity evaluation of a new Neospora caninum strain from naturally infected goats

Abstract

Neospora caninum is an apicomplexan protozoan, known worldwide as a important causative agent of abortions in livestock, especially dairy cattle, causing only in Brazil estimated losses of $ 51.7 million annually in dairy farms, and $ 101 million in beef cattle. In 2013, considering 10 countries, annual losses reached an estimated value of $ 1.298 billion. Clinically neosporosis is manifested in the intermediate host, as recurrent miscarriages. In cattle, abortion usually occurs within 5 to 6 months of pregnancy, and can cause complications such as mummification and fetal maceration, in the case of non-occurrence of the abortions, the conceptus can be born with or without clinical signs but persistently infected. In the case of infection in goats have been reported, as well as miscarriages and birth of infected animals, the birth of seronegative animals despite the mother being positive. After infection an immune response polarization to Th-1 profile is essential for its control, an immune response mediated by T cells is activated, producing IL-12 and IFN-³. Injuries that cause abortion can be as much fetal as placental. The polarization of the immune response of the mother during pregnancy to T-helper 2 (Th2) is an important factor for maintaining a normal pregnancy, but following infection with N. caninum, it is able to polarize the immune response to T-helper 1 ( Th1), this leads to effective control against the intracellular parasite, but may be incompatible with pregnancy. Although systemic response is mediated by T lymphocytes, in the central nervous system, immunohistochemical markers characterize the cells present in the lesions of gliosis and perivascular cuffs as microglia and blood monocytes with the progressive involvement of astrocytes that multiply near the lesion sites . In adult male goats are also glial lesions but not accompanied by necrotic areas, latter but not active lesions are composed of glial astrocytic scars, but in active areas of gliosis near perivascular cuffs's there is activity of monocytic lineage cells and astrocytes concurrently without the meaningful participation of lymphocytes. There are few reports of pathogenicity of N. caninum strains in goats and even then there is no published data on experimental infections of strains isolated from goats. In a previous work carried out by our study group it's show some unusual behavior in primarily infected male goats during pregnancy, which have moderate degrees of active encephalitis pronounced in adulthood but with no clinical signs, compared to the same herd females, that not presented such lesions with significant frequency demonstrating the importance of studies on male goats, the behavior of the infection and the degree of pathogenicity of this strain in this species and its possible differences compared to other strains commonly used in research. Although there are few reports on the prevalence of the disease in goats, serologic studies in São Paulo point to 19.7/100 infected animals. Due to the interest in elucidating the mechanisms of pathogenicity of N. caninum strains and development of experimental models, this study aims to evaluate the infection processes, pathogenic and immune response in mice (Mus musculus), gerbils (Meriones unguiculatus) and hamsters (Mesocricetus auratus) of a new strain of N. caninum isolated from goats, due to its apparent unusual behavior compared to other strains with already established pathogenicity.