Neospora caninum is a unicellular parasite that induces miscarriages in cows in large parts of the world. Siv Klevar's doctoral thesis has charted both the occurrence of the parasite in Norway and also important immunological processes that occur when herds become infected. The parasite occurs only rarely in Norway, but these immunological findings are of value for the development of a more effective vaccine.
Neospora caninum is a coccidia with a life cycle that includes dogs and coyotes as its only known primary hosts, while dairy cattle are its most frequent interim hosts. Siv Klevar has examined 1657 Norwegian dairy herds with a view to finding antibodies against the parasite. The prevalence in Norway was 0.7% and the herds that tested positive were to be found in the regions of Jæren (in the South West) and Østfold (South East) respectively. In one area in Jæren, 22% of the herds were infected by the parasite. The results of this study show that the parasite is not a major cause of miscarriages in dairy herds in Norway. But in certain areas, there is reason to believe that Neospora caninum may be the cause of problems connected with miscarriages in dairy herds.
Siv Klevar's charting of the immunological processes that occur in cases of Neospora caninum infection in cattle has revealed new mechanisms which may encourage further research into the interaction between the host animal and the parasite.
Natural killer (NK) cells in the hereditary immune defence system are important when it comes to fighting these microorganisms. In three different studies, Klevar has examined NK cells from cattle infected with Neospora caninum. The results show that NK cells are an important factor in the first-line defence system against this type of infection in cattle.
One laboratory experiment revealed that NK cells killed infected cells. In addition, NK cells were directly activated by intact parasites. Neospora caninum were shown to be one of only a few microorganisms that can directly stimulate NK cells. These laboratory findings were corroborated by an experimental infection of calves.
In another laboratory experiment, Klevar and her assistants studied how the closely related parasites Toxoplasma gondii and Neospora caninum both stimulated NK cells. They found that intact Toxoplasma gondii, in contrast to Neospora caninum, did not have the effect of stimulating NK cells. Water-soluble structures from both parasites were shown to inhibit activation of NK cells. This is an interesting finding because it reveals that parasites can both inhibit and activate parts of the host's immune response. Further knowledge of these mechanisms can be useful when it comes to developing a more effective vaccine against Neospora caninum.
Siv Klevar, Cand.med.vet., defended her doctoral thesis on 4th February 2011 at The Norwegian School of Veterinary Science. The thesis is entitled "Neospora caninum -- prevalence in Norwegian dairy herds and immune responses with emphasis on parasite-NK cell interactions."
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