Sporadic bovine encephalomyelitis (SBE) is reported in various parts of the world. The disease primarily affects cattle 1 yr old, resulting in neurologic signs and polyserositis.
Etiology and Epidemiology
SBE is caused by Chlamydophila pecorum. Subclinical intestinal infections in cattle and other animals may be the source of infection in SBE. The disease is most often seen in calves <6 mo old and rarely in older cattle. Morbidity rates are usually low but can reach 50%; many sick calves die if not treated at an early stage.
The incubation period in experimentally infected calves is 6–30 days. The first sign in natural and experimental cases is fever (104–107°F [40–41.7°C]). Appetite remains good for the first 2–3 days despite the fever. Afterward, depression, excess salivation, diarrhea, anorexia, and weight loss occur. Calves first appear stiff and may knuckle at the fetlocks. Calves become incoordinated and stagger or fall over objects. Head pressing and blindness are not seen. In the terminal stage, calves are frequently recumbent and may develop opisthotonos. The course of the disease is usually 10–14 days.
Lesions are not limited to the brain; vascular damage can be seen in many different organs. Serofibrinous peritonitis, pleuritis, and pericarditis are common and are especially pronounced in more chronic cases. Microscopic lesions in the brain consist of perivascular cuffs and inflammatory foci in the parenchyma composed primarily of mononuclear cells.
A tentative diagnosis can be based on clinical signs and particularly on the presence of serofibrinous peritonitis in the absence of other causes of peritonitis such as intestinal volvulus, intussusception, traumatic perforation of the reticulum, perforated abomasal ulcer, or displaced organs. Differential diagnoses also include rabies, infectious bovine rhinotracheitis with encephalitis, listeriosis, thromboembolic encephalomyelitis, polioencephalomalacia, pseudorabies, paramyxovirus encephalomyelitis, and malignant catarrhal fever. A diagnosis of SBE is confirmed by isolation of the organism from brain tissue in either developing chicken embryos or cell cultures, by histologic changes in brain sections, by evaluation of tissue impression smears after Giemsa or immunofluorescent staining, or by demonstration of Chlamydophila DNA via PCR testing.
The antibiotics of choice are tetracyclines, oxytetracyclines, and tylosin. For treatment to be effective, it must be given as early as possible in high doses (eg, oxytetracyclines at 10–20 mg/kg/day) and for ≥1 wk. If treatment is effective, the fever should drop significantly within 24 hr. No vaccines are available.
Last full review/revision July 2011 by Robert J. Callan, DVM, MS, PhD, DACVIM