Page 956 - Clinical Small Animal Internal Medicine

894 Section 9 Infectious Disease

Rabid animals may exhibit a combination of excitatory effective against rabies. Secure isolation and observa-
VetBooks.ir and paralytic signs, in which disorientation and anxiety tion, or euthanasia, of the suspect rabid animal is the pri-
mary clinical intervention.
may be coupled with restlessness and weakness. Some ani-
mals die acutely. Most rabid animals eventually progress
to generalized paralysis, respiratory arrest, and death.
Prognosis

Diagnosis Grave – rabies is fatal.

There is no validated test available for diagnosing rabies in
a clinically ill, living animal. The direct fluorescent anti- Prevention
body (DFA) test is the gold standard for diagnosing rabies,
and is performed on brain tissue. This test is almost always A robust immune response is the only effective defense
performed by a public health laboratory, and is the test against rabies. Standard rabies vaccination, when admin-
that must be used when human rabies exposure is possi- istered through proper protocols, affords protection
ble. For most species, the DFA test requires submission of against all variants. Vaccine failure does occur, but is
the head or whole brain. When decapitation or debraining very rare.
is required, only trained, rabies‐vaccinated staff should Numerous vaccines are licensed for use in the US.
perform the procedure. Keep the specimen fresh and Vaccines are either inactivated (killed) or recombinant,
refrigerated; fixation with formalin renders it untestable in which a live canarypox virus expresses rabies proteins.
by DFA. Freezing the sample will delay testing and compli- Most rabies vaccines are first administered at age 3
cate performance of the test. For bats, the entire body may months, boostered a year later, and then every one or
often be submitted. The laboratory should be contacted in three years thereafter. The vaccine label should be
advance for requirements on specimen preparation, ship- reviewed carefully for the exact protocol required. Adult
ping, and submission. dogs or cats being vaccinated for the first time should
Serology is not useful in the diagnosis of clinical rabies have a booster a year later. An animal is considered
in animals. Patients previously vaccinated against rabies immunized about four weeks after its first rabies vacci-
before the illness may have positive titers. Young, unvac- nation, or immediately after a booster.
cinated animals may have measurable maternal antibod- Indoor‐only cats should be vaccinated against rabies.
ies against rabies, clouding interpretation. Insectivorous bats, an important rabies reservoir in
Fixed brain tissue may be examined for rabies through North America, are sometimes found inside buildings.
immunohistochemistry (IHC) by certain laboratories. In Los Angeles County (where the authors work), at least
Histopathology may reveal Negri bodies in rabies‐ one rabid bat is identified indoors every year.
infected neurons, but they are not consistently present. The risk of injection‐site fibrosarcoma exists when
Polymerase chain reaction (PCR) testing is used as an vaccinating cats. Recombinant vaccinations appear to be
antemortem test for rabies in people. The test is usually associated with a lower risk than killed vaccines.
performed on saliva and on skin from the back of the All states require rabies vaccination for dogs, and sev-
neck of the human patient. The sensitivity of PCR testing eral require vaccination of cats. Individual cities or coun-
on tissue outside the CNS is too low to be used to make ties may require vaccination of cats even when their state
decisions in managing a potential rabid animal, and is does not require it. Some states allow exemption from
not routinely used in animals because of the risk to pub- rabies vaccination in cases where it may present a severe
lic safety. PCR testing may be used to supplement DFA risk to the health of the animal. The criteria for granting
testing on brain matter. exemption, and the protocol for obtaining one, vary by
A direct, rapid immunohistochemical test (DRIT) is state and locality. Note that rabies serologic testing is not
used during surveys of rabies in wildlife. accepted in lieu of vaccination in most areas of the US.
There is no test available for evaluating healthy ani- Vaccination is not the only way to reduce the risk of
mals for exposure to rabies, primarily because the virus rabies exposure. Encourage clients to keep dogs leashed
usually remains localized and undetected by the immune when off property, and to keep cats indoors. Clients can
system during much of the incubation period. reduce the attractions for wildlife on their property by
keeping all pet food (and other consumables) and water
indoors, by bat‐proofing their home, and by keeping
Therapy crawl spaces and the underside of decks sealed off.
Clients who rescue stray, feral or wild animals, and
If an animal is rabid, all clinical interventions will fail and especially those who may participate in international
the animal will die. No antivirals have been shown to be rescue efforts, may face a higher risk of rabies exposure.