Submitted to: International Journal for Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/6/1999
Publication Date: N/A
Citation: Interpretive Summary: Neospora caninum is the major cause of abortion in cattle in many parts of the world. Recently, it has been shown that dogs excrete the infective stage (oocyst) of this parasite and thus serve as a host for this parasite. The aim of this study was to investigate whether calves can be infected with these oocysts from Neospora and if calves develop antibodies or cells which recognise Neospora antigens. Before infection, none of the calves showed antibodies which recognised Neospora antigens and none of them had cells reacting to Neospora antigens. However, after 1 week of infection the infected calves had cells that recognized antigens from Neospora and within 2 and 4 weeks also antibodies against Neospora were also detected. The presence of antibodies and cells in the infected animals, and parasite DNA in the brain and spinal cord, indicate that the cattle were infected upon receiving N. caninum oocysts collected from dogs. In contrast calves not given oocysts showed none of these changes. To our knowledge this is the first report of an experimental infection of calves with Neospora oocysts.
Technical Abstract: Neospora caninum has been identified as a major cause of abortion in cattle in a number of countries throughout the world. Until the recent demonstration that dogs can serve as a definitive host of this parasite, it was not possible to study the infection in cattle orally exposed to oocysts. The aim of this study was to investigate the potential of N. caninum oocysts to infect calves and to define initial immune responses that arise after oral infection. Seven calves were fed approximately 104-105 N. caninum oocysts, three calves served as uninfected controls. Before infection, all calves were serologically negative for anti-Neospora antibodies and the calves were non-reactive to Neospora antigen in an in vitro lymphocyte proliferation assay. Peripheral blood lymphocytes from inoculated calves were able to mount in vitro proliferative responses to crude N. caninum antigen extract as early as one week p.i. Within 2 and 4 weeks p.i. Neospora-specific IgG1 and IgG2 antibodies were detected by IFAT and ELISA in serum from infected calves but not from sham-infected calves. The continued presence of reactive cells in the blood, spleen and mesenteric, inguinal, bronchial lymph nodes was seen as late as 2.5 months p.i., and parasite DNA was detected in the brain and spinal cord of the infected animals by PCR, indicating that the cattle were infected by oral inoculation of N. caninum oocysts collected from dogs, and that the animals were systematically sensitised by parasite antigen.