First report of acute, visceral, fatal toxoplasmosis in a naturally infected calf (Bos taurus).

Cattle are considered resistant to clinical toxoplasmosis and viable Toxoplasma gondii is rarely isolated from bovine tissues. Currently, there is no histologically confirmed case of clinical toxoplasmosis in cattle. Here, the first confirmed case of acute toxoplasmosis in cattle is reported. A calf from New Zealand died of acute toxoplasmosis in 2012. Severe lesions were found in the intestinal mesentery and mesenteric lymph nodes. The mesenteric lymph nodes were edematous, and necrosis affected the entire parenchyma including blood vessels, associated with enormous numbers of tachyzoites. Lesions in liver were inflammatory, affecting periportal areas and central veins. Some hepatocytes were engorged with tachyzoites, and tissue cysts were present in the parenchyma. Focal pneumonitis and nephritis were associated with tachyzoites. Tachyzoites were seen in bronchioles, in renal glomeruli and in renal tubules. Diagnosis was confirmed immunohistochemically using T. gondii specific antibodies, but not Neospora caninum -specific antibodies. The presence of numerous tissue cysts was confirmed by immunohistochemical staining with bradyzoite-specific T. gondii antibodies (BAG1).