In a necropsy scenario with two adult cattle showing hemoglobinuria and a large liver infarct, which organism is most likely the causative agent?

• A. Weaponized anthrax
• B. Clostridium chauvoei
• C. Bacillus anthracis
• D. Clostridium hemolyticum

Answer: (D)

Bacillary hemoglobinuria (redwater disease) is the pattern here. In cattle, a large liver infarct with intravascular hemolysis and hemoglobinuria points to infection with Clostridium haemolyticum. The story is that liver damage from flukes creates an anaerobic niche in which this organism can proliferate and release a beta-toxin that lyses red blood cells, causing the dark urine and pigment deposition, while the liver infarcts come from the same hepatic injury and bacterial activity. This combination—hemoglobinuria plus a pronounced liver infarct on necropsy—is classic for C. haemolyticum.

The other agents don’t fit as well. Blackleg from Clostridium chauvoei causes severe muscle necrosis and gas formation rather than marked hemoglobinuria and liver infarcts. Anthrax agents (Bacillus anthracis) cause rapid septicemic hemorrhages and widespread edema or dark, unclotted blood, not a characteristic single large liver infarct with redwater. So the pattern best aligns with Clostridium haemolyticum causing bacillary hemoglobinuria.