Among the pathogens commonly involved in bovine respiratory disease (BRD) complex, Histophilus somni is not as prevalent as Mannheimia haemolytica or Pasteurella multocida, but the pathogen is highly virulent and can cause a range of clinical disease presentations in cattle.
During the Academy of Veterinary Consultants conference last week, Breck Hunsaker, DVM, PhD, with Feedlot Health and Management Services in Idaho, outlined research showing the pathogen can turn up in cattle from a wider range of sources than many suspect.
Hunsaker says the pathogen, in addition to presenting as respiratory disease, can cause reproductive disease resulting in infertility and abortions, a septicemic form causing lameness, swollen joints and heart disease, and a nervous form including thrombotic meningoencephalitis (TME), which sometimes occurs in feedyard cattle three to four weeks after arrival.
H. somni is typically considered a northern pathogen, primarily affecting cattle from Canada and the northern United States. However, Husaker’s group conducted a review of databases for post-mortem diagnosis of H. somni in feedyard cattle over several years and found some surprising trends. The review cataloged mortality as a proportion of placements from regions across the United States and Canada.
In 2009, the review showed a higher incidence of H. somni mortality in the United States than in Canada, and by far the highest incidence that year was in cattle sourced from the Southeastern United States.
In 2010, the incidence in cattle sourced from or fed in Canada topped that of U.S.-sourced cattle, but within the United States, cattle sourced from the Southeast again had the highest incidence.
In 2011 and 2012, the highest incidence shifted from Southeastern-sourced cattle to those coming from the Northeast. Over the years covered in the review, the incidence of reported H. somni declined overall in U.S. cattle, and particularly in cattle from the Southeast.
Hunsaker says management against the pathogen can include vaccination prior to shipment to the feedlot, although most vaccines are labeled for protection again TME only, not the other forms of disease. In the feedyard, metaphylaxis based on risk upon arrival offers the most effective control strategy.