Primary infection of goats with Eimeria ninakohlyakimovae does not provide protective immunity against high challenge infections

Coccidiosis caused by the apicomplexan protozoa Eimeria ninakohlyakimovae has a high impact on animal health and profitability of the goat industry worldwide. Primary E. ninakohlyakimovae infections induce clinical disease mainly in goat kids, as homologous re-infections are commonly under immunological control. Nevertheless, there is evidence of fatal acute E. ninakohlyakimovae challenge-infections to occur in goat kids. So far, the nature of the immune response promoting protection or failure in E. ninakohlyakimovae challenge-infected goat kids has not been investigated. Therefore, we here analyzed cellular immune responses and histopathological alterations in the gut mucosa of fatal E. ninakohlyakimovae challenge-infected goat kids. Overall, a severe eosinophilic enteritis was observed in affected animals. Hyperplasia of epithelial cells, hypertrophy of globet cells and marked hyperplasia of Peyer's patches and mesenteric lymph nodes draining affected areas were also relevant findings. The majority of goat kids suffering from acute E. ninakohlyakimovae challenge-infections showed severe diarrhoea and some of them even died within 11-16 days post challenge, indicating that the mechanisms of pathogenicity might be related to the first generation macromeronts. Interestingly, infiltration of eosinophils and, in less extent, of intraepithelial lymphocytes and neutrophils was observed even within degraded E. ninakohlyakimovae first generation macromeronts. The excessive immune response mounted against intracellular E. ninakohlyakimovae stages (sporozoites/meronts I) as measured by intestinal leucocyte infiltration might result in severe pro-inflammatory reactions and contribute to the fatal outcome of the challenge infection.