Sporadic Bovine Encephalomyelitis: Introduction
(Chlamydial encephalomyelitis) |  |
| Outbreaks of sporadic bovine encephalomyelitis (SBE) have occurred in various parts of the world. Reports indicate that chlamydiae can also cause infections of the brain in humans, opossums, dogs, and several avian species. |
| Etiology and Epidemiology: |
| SBE is caused by the species
Chlamydophila
pecorum
. Subclinical intestinal infections in cattle and other animals are probably much more common than reported and may well be the source of infection in SBE. It is not understood why, in sporadic cases, chlamydiae leave a balanced host-parasite relationship in the intestine, penetrate the intestinal barrier, establish a blood-infectious phase, and infect the brain as the target organ. |
| The disease is most often seen in cattle 3 mo to 3 yr old. Morbidity rates are usually low but can reach 50%; many sick calves die if not treated at an early stage. |
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| Clinical Findings: |
| The incubation period in experimentally infected calves is 6-30 days. The first sign in natural and experimental cases is fever (104-107°F). The temperature remains increased until shortly before death or recovery. Appetite remains good for the first 2-3 days despite the fever. Afterward, depression, excess salivation, diarrhea, anorexia, and weight loss occur. Calves are 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:
| 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. |
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| Diagnosis: |
| A tentative diagnosis can be based on clinical signs and particularly on the presence of a 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, 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. |
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| Treatment: |
| 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 20-50 mg/kg/day) and for ≥1 wk. If treatment is effective, the fever should drop significantly within 24 hr. Vaccines are not available. |
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