Listeriosis in a goat doe
Guy Sheppard DVM, Jessie Monday DVM, MS, Laura Rice DVM, MS, DACVP
Samples from a one-year-old Boer goat doe were received at the TVMDL for testing. The doe had displayed neurological signs including unilateral paresis, droopy lip and hypersalivation, torticollis upon stimulation, obtundation, and lateral recumbency. The goat was also febrile. Clinical differentials included listeriosis, polioencephalomalacia, bacterial meningitis, and rabies virus. Treatment consisted of antibiotics, anti-inflammatory drugs, and vitamins B1 and B12. The patient responded to initial treatment and supportive care.
The goat died the following day, and tissues were submitted to TVMDL for diagnostic investigation. Due to the fact that several people were exposed to saliva from this goat, sections of the brain were submitted to the Texas Department of State Health Services for rabies testing.
After a negative rabies test result was received, histopathology exam of the brain tissue was conducted along with a culture of the brain tissue. The most significant finding on histopath was necrosuppurative meningoencephalitis (Figure 1), and Listeria spp. was isolated and identified from the culture.
Listeria monocytogenes, the cause of encephalitic listeriosis, can also cause abortions, neonatal septicemia, ophthalmitis, and mastitis in small ruminants. L. monocytogenes are gram-positive, non-acid-fast facultative microaerophilic bacteria ubiquitous in outdoor environments of temperate climates. The bacteria can be shed in feces, tears, nasal secretions, uterine fluid, and milk. Bacteria can remain viable in soil, feces, and contaminated feed for months to years.
Neurologic listeriosis in ruminants can manifest as focal, multifocal, or diffuse encephalitis, meningoencephalitis, or myelitis. Encephalitis localized to the brain stem is the most frequently recognized syndrome in small ruminants. Sheep and goats often present acutely with asymmetric central nervous system signs including ataxia, circling, head pressing, depression, and other neurologic examination abnormalities consistent with meningitis and focal brainstem lesions (microabscesses). Cranial nerve abnormalities, including unilateral nasal deviation, lip droop, dropped jaw, ear droop, head tilt, dysphagia, unilateral tongue paresis, and eyelid droop are common. Exposure keratitis can occur secondarily to the cranial nerve abnormalities. Metabolic abnormalities, dehydration, decreased rumen motility, and metabolic acidosis secondary to decreased salivary bicarbonate are potential clinical sequela to manage.
Clinical signs can vary depending on the location of lesions and the duration of infection. Clinical disease progression is rapid and severe, with a high fatality rate. The disease in small ruminants tends to be more acute and more often fatal when compared to neurologic listeriosis in cattle. The disease usually affects only one or two animals in a population but outbreaks with multiple fatalities in a herd have been reported.
Antemortem testing options include cerebral spinal fluid (CSF) cytology, CSF culture or L. monocytogenes rtPCR, CBC, and chemistry profile.
Listeriosis is a common diagnostic laboratory diagnosis in postmortem caprine cases submitted for work up of neurologic disease in the United States. Bacterial culture for Listeria spp. from appropriate fresh tissue samples is more successful in small ruminants than cattle. In cases where Listeriosis is the primary differential but culture fails to recover Listeria spp., IHC for listerial antigens can prove useful, even in cases lacking significant or pathognomonic histopathology lesions. Molecular testing (rtPCR) is also a sensitive methodology that can be applied to diagnostic investigations before, concurrent with, or after histopathology and culture. Postmortem CSF fluid can also be diagnostically rewarding when submitted for cytology or pathogen detection via rtPCR if brain tissue is not available. Culture and rtPCR of CSF is less often rewarding compared to appropriate sections of affected fresh brain tissue.
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