Encefalomielite bovina esporádica

Sporadic bovine encephalomyelitis is caused by C pecorum biotype 2, an obligate intracellular bacterium. Genetically identical C pecorum isolates have been identified from clinical cases in geographically different areas.

C pecorum isolates from clinical cases are distinct from those found in the GI tract of clinically normal animals. These findings indicate that subclinical intestinal infections in cattle and other animals might not be the source of infection in SBE.

SBE occurs most often in calves < 6 months old and less commonly in older cattle. Sporadic cases and outbreaks can occur within individual herds.

SBE morbidity rates are most commonly < 25% but can reach 50%. Mortality rates can approach 30% and are highest in younger calves (1). Many sick animals die if not treated at an early stage of the disease.

The incubation period for sporadic bovine encephalomyelitis in experimentally infected calves is 6–30 days. The first sign in natural and experimental cases is fever (40–41.7°C [104–107°F]).

The affected animal's appetite remains good for the first 2–3 days despite the fever. Then, depression, excess salivation, diarrhea, anorexia, and weight loss occur. Nasal discharge and respiratory signs due to pleuritis can occur as well. Early neurological signs of SBE include depression, stiffness with knuckling at the fetlocks, decreased tail tone, and incontinence.

Calves with SBE progressively become uncoordinated and stagger, circle, or fall over objects (see circling calf video). Head pressing, blindness, and decreased pupillary light reflexes are typically not observed, which helps differentiate this condition from other common causes of neurological disease in calves.

Encefalomielite bovina esporád...

Vídeo

In the terminal stage of SBE, calves are frequently recumbent and can develop opisthotonos. The course of the disease is usually 10–14 days.

• Clinical examination

• Bacterial culture

• PCR assay

A tentative diagnosis of sporadic bovine encephalomyelitis can be based on clinical signs, particularly 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 include the following:

• infectious bovine rhinotracheitis with encephalitis

• listeriosis

• malignant catarrhal fever

• nervous coccidiosis

• otitis interna

• paramyxovirus encephalomyelitis

• polioencephalomalacia

• pseudorabies

• rabies

• thromboembolic encephalomyelitis

SBE can be diagnosed by PCR detection of C pecorum DNA in brain tissue, pleural fluid, pericardial fluid, or peritoneal fluid of affected animals. Diagnosis can also be confirmed by culture either in developing chicken embryos or in cell cultures, by histological examination of brain sections, or by evaluation of tissue impression smears after Giemsa or immunofluorescent staining.

• Supportive care

• Antimicrobials

Tetracyclines and tylosin are the antimicrobials of choice for treatment of sporadic bovine encephalomyelitis.

For treatment to be effective, it must be administered as early as possible, at the upper threshold of labeled dosing guidelines. If treatment is successful, the fever should drop appreciably within 24 hours.

No vaccines are available.

• Sporadic bovine encephalomyelitis should be considered in calves presenting with a combination of neurological signs and polyserositis.

• Treatment consists of antimicrobials and supportive care.

1. Cantile C, Youssef S. Nervous system. In: Maxie GM, ed. Jubb, Kennedy & Palmer’s Pathology of Domestic Animals. Elsevier Health Sciences; 2015:250-406.