Bacillary hemoglobinuria in beef cattle infected with Fascioloides magna in Missouri.

Bacillary hemoglobinuria (BH) is an infectious disease, mostly affecting cattle, caused by Clostridium haemolyticum ( C. novyi type D), with acute hepatic necrosis and intravascular hemolysis. Cattle are typically predisposed to BH by liver injury caused by Fasciola hepatica , although cases have been reported in cattle without evidence of this parasite. Here we describe a cluster of 14 BH cases from 7 counties in north-central to central Missouri submitted to a veterinary diagnostic laboratory between December 2020 and April 2023. Postmortem examination in all cases revealed hemoglobinuria and acute hepatic necrosis with large numbers of gram-positive bacilli with terminal-to-subterminal spores. Flukes, fluke ova, and/or fluke pigment consistent with Fascioloides magna were identified in 12 of 14 cases. Sequences of the nuclear ribosomal internal transcribed spacer 1 (ITS1) from one fluke had 100% identity to F. magna. C. novyi was detected by fluorescent antibody testing of liver impression smears (11 of 12 cases) and by immunohistochemistry of liver sections (7 of 7 cases). PCR on formalin-fixed, paraffin-embedded tissues amplified the C. haemolyticum beta toxin gene in each of the 7 cases tested. To our knowledge, a confirmed cluster of BH associated with F. magna has not been reported previously in cattle.