Bacillary hemoglobinuria in beef cattle infected with <i>Fascioloides magna</i> in Missouri

Bacillary hemoglobinuria (BH) is an infectious disease, mostly affecting cattle, caused by <i>Clostridium haemolyticum</i> (<i>C. novyi</i> type D), with acute hepatic necrosis and intravascular hemolysis. Cattle are typically predisposed to BH by liver injury caused by <i>Fasciola hepatica</i>, 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 <i>Fascioloides magna</i> were identified in 12 of 14 cases. Sequences of the nuclear ribosomal internal transcribed spacer 1 (ITS1) from one fluke had 100% identity to <i>F. magna. C. novyi</i> 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 <i>C. haemolyticum</i> beta toxin gene in each of the 7 cases tested. To our knowledge, a confirmed cluster of BH associated with <i>F. magna</i> has not been reported previously in cattle.