Neospora caninum Immunogens against Neosporosis
Neospora caninum, the parasite that causes neosporosis, is known worldwide as one of the main drivers of abortion in cattle herds, causing economic losses when raising livestock. Parasitic infection and transmission among animals are difficult to combat, and both diagnostics and controls must be applied to reduce the spread of the pathogen. For control, herd vaccinations represent an alternative, but the current lack of a safe and effective vaccine prevents this method. The parasite has a significant array of structural proteins that assist in the process of infection; surface antigens (SAGs), microneme proteins (MICs), dense granule antigens (GRAs) and rhoptria proteins (ROPs). Antigens from these proteins are currently being studied as immunogens; they are tested alone or in associations, in order to evaluate the induced immune response in animal models. In experimental vaccine studies, different approaches are used in the formulations, such as live vaccines, DNA vaccines, vaccines using biological vectors, and recombinant subunit vaccines (usually developed with the aid of reverse vaccinology). The contrasts observed (in both cytokine levels and protection rates against vertical transmission), in vaccinated and then challenged (N. caninum), laboratory animals show the complexity of parasite invasion mechanisms, and reveal the need for further research to isolate an effective vaccine to protect cattle against the parasite.
The main problem of neosporosis in cattle is its persistence by means of vertical transmission in asymptomatic animals, especially in the absence of a definitive host. Moreover, the economic impact of neosporosis, is mainly due to its causing abortions as a result of this same asymptomatic transmission because there are no further expenses (such as those with control programs), when disposing infected females from the herd, even when including their treatment.
Seeking to control infection and transmission of this disease in cattle herds, various experimental vaccines are being developed with formulations containing; living parasite, biological vectors, DNA vaccines, and recombinant subunit vaccines, (usually proteins related to the invasion process). Assays based on immunization in animals models (usually mice) focus on the ability of these vaccines to induce a protective response which prevents infection by the parasite, (and especially its vertical transmission), through stimulating cytokine production, critical for both the cell-mediated immune response (e.g., IFN-γ and TNF-α) and humoral immune response (e.g., IL-4 and IL-10).
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Journal of Vaccines & Vaccination