Bovine gastric mucormycosis caused by <i>Rhizopus microsporus</i> in Japanese Black calves

Rhizopus microsporus is an opportunistic fungus that causes pneumonia and gastroenteritis in humans. This report describes two cases of mycotic gastritis caused by R. microsporus in Japanese Black calves. They exhibited diarrhea, wasting, and astasia. At necropsy, adhesion was observed between the abomasum and the abdominal wall (No. 1), and between the rumen and the spleen (No. 2). Histopathologically, severe necrosis with many mucoraceous fungi was observed in the abomasum (No. 1) and the rumen (No. 2), with fibrous granulation tissue forming in each adhered region. Molecular analysis identified both fungi as R. microsporus. Thymus hypoplasia was likely a predisposing factor, facilitating infection alongside the injury due to gastric catheter use and complications of white muscle disease.