Bovine thrombotic meningoncephalitis
Guy Sheppard, DVM and Andrés de la Concha-Bermejilla, DVM, MS, PhD
Bovine thrombotic meningoencephalitis (TEM), formerly known as thromboembolic meningoencephalitis (TEME), is a neurological disease, primarily of feedlot cattle between the ages of 6 to 12 months. The condition is caused by Histophilus somni (previously known as Haemophilus somnus), a Gram-negative opportunistic bacterium that can be cultured very commonly from the respiratory and reproductive tracts of normal cattle. Calves are infected by carrier cows early in life and later spread the infection at the feedlot. Observed symptoms of infection reflect abnormalities in the system affected. When pregnant cows get infected, they can abort.
In the case of TEM, it is thought the organism gains entry to the body through the respiratory tract before moving into the nervous system. Onset of disease can range from acute death without premonitory signs to chronic disease.
The neurological form of infection is characterized by fever, depression, ataxia, and recumbency. Opisthotonus, nystagmus, strabismus, blindness, hyperesthesia, and convulsions may also be noted. Symptoms usually develop in the first 3-4 weeks after arrival at the feed yard.
Neurological lesions are characterized by brown to red hemorrhagic infarcts at the gray-white matter interface of the cerebrum and thalamus. In addition, infection with H. somni can result in fibrinopurulent bronchopneumonia, myocarditis, necrotizing laryngotracheitis, mastitis and polyarthritis. Microscopic lesions are characterized by necrotizing vasculitis and thrombosis. Vessels in the cerebrum, brain stem and spinal cord contain poorly organized thrombi rich in neutrophils. The surrounding parenchyma exhibits areas of severe hemorrhage, necrosis and infiltration of neutrophils and macrophages. Often, bacterial colonies can be observed in the lesions. Fibrin thrombi and fibrinopurulent inflammation also can be found in the meninges, myocardium, joints and lung,
The diagnosis is established by clinical signs, gross and microscopic lesion and by isolation of the organism. The Texas A&M Veterinary Medical Diagnostic Laboratory’s (TVMDL) can detect H. somni nuclei acid in affected organs by rtPCR as part of the bovine bacterial respiratory panel or as an individual test. The differential diagnosis includes other neurological diseases of cattle including polioencephalomalacia, lead poisoning, salt poisoning, listeriosis, bovine herpesvirus encephalomyelitis, rabies and others.
Treatment of affected cattle involves supportive care and use of antibiotics that will cross the blood-brain barrier. Treatment is more successful if the animal is in the early stages of the disease process.
To learn more about TVMDL’s test offerings for bovine diseases, visit tvmdl.tamu.edu or call 1.888.646.5623.
Janzen E. Histophilus somni Complex, Blackwell’s Five-Minute Veterinary Consult: Ruminant; 3 C. Chase, consulting editor. Willey Blackwell. Second Ed. 2017, pgs 390-393.