Histophilus somni Bovine Respiratory Disease complex, bronchopneumonia, Thromoembolic meningoencephalitis TEME Histophilus somni Haemophilus somnus is a common disease-causing bacterium of cattle, with a large proportion of cattle carrying antibodies to the organism. Respiratory infection often precedes infection of other organ systems. The respiratory, genital, nervous brainers, thromboembolic meningoencephalitis, TEME , circulatory, and musculoskeletal systems joints can be affected, either individually or together. In some areas, H. The incidence of any of the H.

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It appears microscopically as a cocco-bacillus, is a facultative anaerobe, non-motile, and a non-spore-forming bacteria. Infection with H. Young growing cattle age months are most commonly infected and show clinical signs. The actual prevalence of the bacteria is very high, and almost all cattle will be exposed at some point in their life. Clinical disease can be devastating when it occurs. Historically, the most common disease manifestation was TME but, in recent years, respiratory disease and myocarditis are becoming more prevalent.

The bacteria require a breakdown in mucosal immunity in order to cause disease. Many different types of events can compromise the immunity of a beef calf. These may include stress from transport, concurrent viral infection, inclement weather, weaning, etc. Certain virulence factors play a role in the disease process as well. The pathogenesis of TME involves a bacterial septicemia. Once the bacteria enter the bloodstream, they are able to evade host defenses and cause apoptosis of bovine endothelial cells.

In the heart this can cause myocarditis with multiple infarcts, necrosis, and abscessation. Clinical signs of cattle with H. Calves with neurologic disease TME will often times be acutely affected and sudden death may be the only clinical sign.

Other clinical signs that may be observed are fever, depression, lateral recumbency, and closed eyes "sleeper syndrome". If animals are still able to stand they will be ataxic, weak, and may appear blind.

Regardless of the clinical signs, the course of the disease is rapid and most affected animals will die within 24 hours. The progression of disease in calves with myocarditis is also very rapid and sudden death may be the only clinical sign.

A clinical diagnosis of myocarditis is rarely made, with affected cattle potentially showing signs of left heart failure exercise intolerance, open-mouth breathing, cough, etc.

Cattle exhibiting signs of the respiratory form of the disease show nonspecific signs consistent with any pneumonic calf. Affected animals will be febrile, off-feed, show labored breathing, etc. Post mortem examination of cattle that have suffered from H.

The most striking gross lesions will be seen in cattle with either myocarditis or respiratory disease. The left ventricular free wall is most commonly affected and will show full thickness myocardial pallor. Evidence of pulmonary congestion and edema may be noted as well.

Lungs of infected cattle will exhibit a suppurative broncho-pneumonia with fibrinous pleuritis. Gross lesions of cattle with TME may be difficult to see and can be highly variable. Areas of hemorrhage and necrosis may be seen on the surface of the brain or on cut section. The brain itself may also be swollen secondary to edema. Microscopic lesions in all affected organs include vasculitis, neutrophilic inflammation, and tissue necrosis.

Colonies of Gram-negative bacteria may be seen in thrombi. Definitive diagnosis of H. These include bacterial culture, serology, and immunohistochemistry. Selective culture media is needed to ensure growth of the bacteria and samples should ideally be taken from untreated animals.

Bacterial culture remains the gold standard for diagnosing H. Serology may also be used to make a definitive diagnosis of H. Therefore, acute and convalescent titers are needed to make a definitive diagnosis which is often times impossible due to the rapid course of the disease.

Finally, immunohistochemistry may be used to identify H. Treatment for all forms of the disease complex have often been with oxytetracycline. Oxytetracycline has been effective in the treatment of TME when the drug is given at the onset of clinical signs.

Treatment is often unsuccessful when antibiotic therapy is delayed or if the animal is already recumbent. Treatment of bronchopneumonia associated with H. The bacteria are also susceptible to many of the antibiotics commonly used to treat bovine pneumonia, including some of the newer, longer-acting medications. Prevention of the H.

Commercial bacterins are available, but their efficacy is questionable. Field trials to test the efficacy of the vaccine are difficult to perform due to an inability to consistently recreate the disease process.

Most vaccines are labeled for protection again TME only, not the other forms of disease. If calves are to be vaccinated it should be performed prior to entry into the feedlot. Metaphylaxis has also been used to prevent H. Metaphylaxis involves pre-treatment with antibiotics prior to clinical illness. This is often done when calves enter the feedlot. They are given an injection of a long-acting antibiotic that is designed to protect them against infection in the early, most stressful time at the feedlot.

Nathan Ahlemeyer, Class of -edited by Dr. Bacterial meningitis and encephalitis in ruminants. The Haemophilus somnus disease complex Hemophilosis : A Review. Canadian Veterinary Journal Large Animal Internal Medicine, 4th ed. Bradford Smith. Pathologic Basis of Veterinary disease, 4th ed.

McGavin and Zachary, Siddaramppa S, Inzana TJ: Haemophilus somnus virulence factors and resistance to host immunity. Animal Health Research Reviews 5 1 : Wessels J, Wessels ME: Histophilus somni myocarditis in a beef rearing calf in the United Kingdom. Veterinary Record


Overview of Histophilosis








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