Page 1091 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1066 CHAPTER 10

VetBooks.ir and sudden death. The most commonly reported The gold standard for diagnosis is an indirect fluo-
rescent antibody test on brain tissue that accurately
signs in horses are hyperaesthesia and recumbency.
Sometimes, neurological abnormalities are not evi-
nation of haematoxylin and eosin-stained brain sec-
dent early in the disease, and early rabies may mimic diagnoses 98% of clinical cases. Microscopic exami-
other conditions such as an acute abdominal viral tions may reveal non- suppurative encephalitis and
infection. The disease is normally rapidly progressive Negri bodies, which are diagnostic (Fig. 10.22).
once signs are seen and results in death in 3–10 days. Intracerebral inoculation of mice is also considered
Evidence of a recent animal bite is rarely present. an accurate method of diagnosis.

Differential diagnosis Management
Rabies has many differential diagnoses, including Other than recovery in a presumptive case of exper-
other conditions with signs of grey matter disease imentally produced rabies in a donkey, the dis-
such as polyneuritis equi, herpesvirus myeloenceph- ease is invariably fatal. In the rare situation where
alitis, EPM and Sorghum–Sudan grass poisoning. an ante-mortem diagnosis is reached, the animal
Cerebral diseases, such as hepatoencephalopathy, should be euthanased to avoid further human con-
leukoencephalomalacia, alphavirus encephalitides, tact. Transmission from horses to humans has never
space-occupying masses and meningitis, should be been reported, but should nonetheless be regarded
considered in some cases. as a possibility and all necessary precautions should
be taken when dealing with animals demonstrat-
Diagnosis ing neurological signs in an endemic area. Affected
Ante-mortem diagnosis of rabies is difficult. horses should be handled as little as possible and
Differentiation of rabies from other encephaliti- only by experienced (and ideally vaccinated) person-
des on the basis of clinical signs is impossible. CSF nel. Barrier precautions, including gowns, gloves and
findings are usually non-specific and can include over-boots, should be worn. Eye protection should
moderate increases in protein, mononuclear cells be considered depending on the clinical presenta-
and occasionally neutrophils. An antigen-capture tion and procedure to be performed. Rabies suspects
enzyme immunodiagnostic technique is available for should be quarantined and prominently identified.
ante-mortem diagnosis using salivary gland speci- Government authorities should be contacted, where
mens, but has not gained widespread clinical use. applicable. Public health authorities should be con-
tacted to coordinate management of exposed humans.
Inactivated annual vaccines are used for protec-
tion of horses in endemic areas. Foals in endemic
10.22
areas should be vaccinated at 4–6 months of age with
two doses administered 3–4 weeks apart, followed
by a booster at 1 year of age. If a previously immun-
ised animal is bitten by a suspected rabid animal,
it can be given three booster immunisations over
1 week and quarantined for at least 90 days. Exposed,
unvaccinated animals of low economic value should
be euthanased immediately. If the animal is valu-
able, confinement and close observation for at least
6 months is necessary. Primary immunisation can be
administered 1 month before release from quarantine.
Fig. 10.22 Histopathological changes associated
with rabies virus infection. Note the Negri bodies Prognosis
(arrow), cellular inclusions that are present in Rabies is always fatal in horses. Death usually occurs
neuronal cell cytoplasm. (Photo courtesy D Perl, 3–10 days following development of neurological
Centers for Disease Control) abnormalities.