Bovine babesiosis diagnosed in formalin-fixed, paraffin-embedded tissues by using in situ hybridization
Bovine babesiosis, caused by <i>Babesia divergens</i>, is in general a rare disease in Europe. Nonetheless, local outbreaks can cause severe economic damage, and postmortem identification represents a diagnostic challenge. During a recent outbreak in May 2018 in northern Germany, 21 animals of a herd of 150 cattle died within 40 days having had clinical signs of fever and hemoglobinuria. Gross examination of 4 of the 21 deceased animals revealed a tick infestation, jaundice, and dark brown staining of urine and kidneys. Histologically, there were iron-positive deposits, hyperplasia of the red pulp of the spleen, and centrilobular necrosis of hepatocytes. In several locations, small basophilic granules suggestive of intraerythrocytic parasites were visible in hematoxylin-eosin- and Giemsa-stained sections. Peripheral blood smears from a living cow from the herd and polymerase chain reaction (PCR) of feeding ticks revealed <i>B. divergens</i> infection. In situ hybridization (ISH) was applied on formalin-fixed, paraffin-embedded (FFPE) tissue of the necropsied cattle to confirm babesiosis in these animals postmortem. Digoxigenin-labeled DNA probes were generated based on a specific nucleotide sequence for <i>B. divergens</i>, obtained by PCR and sequencing of DNA isolates from infected <i>Ixodes ricinus</i> ticks from deceased cattle. ISH using these probes allowed postmortem diagnosis of <i>B. divergens</i> infection in routinely fixed FFPE tissues.