Histo ph il us so mn i i n Ca tt le Contin ue d .. .

An accurate diagnosis of H. somni can be made post-mortem by laboratory analysis of tissue samples collected at necropsy. Fluid and tissue samples for H. somni laboratory analysis can be collected from the blood, cerebral spinal fluid (CSF), joint fluid, urine, brain, heart, kidneys, liver and lungs. Laboratory tests may include bacterial culture, immunohistochemistry, polymerase chain reaction (PCR) and serology.

In a particular field case attended by Dr. Tom Noffsinger of Production Animal Consultation, the symptoms expressed by the affected animal prior to death and the lack of gross lesions found at necropsy could have led to an incorrect diagnosis if no laboratory analysis was performed. The animal presented with brainer-like central nervous system symptoms approximately 24 hours prior to death and was nonresponsive to treatment with thiamine. The necropsy performed by Dr. Noffsinger revealed no gross lesions in the heart. Given this information, the animal could have been misdiagnosed with grain overload, rabies or listeriosis.

Tissue samples were sent to the Kansas State Veterinary Diagnostic Laboratory for analysis. PCR analysis on larynx tissues tested positive for H. somni in addition to M. bovis, P. multocida and B. trehalosi. Negative results were obtained for M. haemolytica, BVD, BRSV, BCoV and BHV-1/IBR. The necropsy histopathology revealed areas of inflammation and necrosis scattered throughout the cerebrum and myocardium, consistent with H. somni infection.

Successful treatment of animals affected by H. somni can be challenging and is highly dependent on early detection of affected animals. However, early detection can itself be difficult given the rapid progression of disease after onset. In vitro studies have shown that H. somni is treatable with a variety of antimicrobials, but as H. somni infection progresses, it is hypothesized that the bacteria develop a biofilm that adheres to the endothelium, creating a defensive front and reducing the effectiveness of antimicrobials. Florfenicol treatment regimens have been shown effective during early stages of respiratory disease associated with H. somni, and oxytetracycline treatment regimens have been successful in animals expressing early stages of TME.

Because of the difficulty associated with early identification and treatment of H. somni infection, prevention practices are key in reducing H. somni outbreaks. Stress reduction through low-stress cattle handling practices; adequate bunk, water and pen space allocation; and increased biosecurity measures including sanitation and reduction of commingling are essential. Proper immunization prior to arrival at the feedlot, metaphylaxis at feedlot entry and prophylaxis may also help protect calves from H. somni infection.

References

Janzen, DVM, MVS, Eugene D. 2013. Overview of Histophilosis, The Merck Veterinary Manual. Accessed February 23, 2015, from http://www.merckmanuals.com/ vet/generalized_conditions/histophilosis/ overview_of_histophilosis.html.

Ahlemeyer, Dr. Nathan. 2010. Histophilus somni Complex in Beef Cattle, Indiana Animal Disease Diagnostic Laboratory. Accessed February 23, 2015, from http:// www.addl.purdue.edu/newsletters/2010/Spring/ histophilus.htm.

Simard, Megan. 2014. An Overview of Histophilus somni in Feedlot Cattle, Veterinary Agri-Health Services. Accessed February 23, 2015, from http://vahs.net/ education/articles/an-overview-histophilus-somni-infeedlot-cattle/.

Zoetis. Histophilus somni. Accessed February 23, 2015, from https://www.zoetisus.com/conditions/beef/histophilussomni-_haemophilus-somnus_-complex.aspx.

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