Histophilosis Myocarditis and Pericarditis.

Histophilosis is a multisystemic bacterial disease in feedlot cattle causing bronchopneumonia, laryngitis, otitis, pleuritis, myocarditis, pericarditis, endocarditis, polyarthritis, and infectious thrombomeningoencephalitis. In western Canada, the most common forms of the disease are myocarditis and pericarditis, which can cause significant mortality in fall-placed feedlot calves. Diagnosis is made on gross pathologic lesions because there are no known live animal tests with good predictive value. None of the licensed Histophilus somni bacterins on the market have been proven effective in reducing mortality. Research continues to understand strain genetic virulence differences to develop effective subunit vaccines to reduce this costly feedlot disease.