The tissues most likely to yield West Nile virus are the heart, kidneys, and central nervous system, particularly the brainstem.
If possible, a section of spinal cord should also be submitted. It is best to formalinize half of each sample and leave the
other half untreated. All tissues should be chilled, not frozen, and shipped expeditiously for West Nile virus polymerase
chain reaction (PCR) or immunohistochemistry testing or both; virus isolation may also be attempted. Be sure to also request
rabies testing for deceased patients suspected of having West Nile virus infection.
For up-to-date information and guidance when dealing with suspected West Nile virus cases, it is advisable to consult both
your state veterinary office and a reference laboratory or state diagnostic laboratory. Also, please report positive results
to the public health department as diagnostic laboratories may not routinely do so.
As with most other viral diseases, no reliable therapeutics target West Nile virus infection. If fever is present, it unlikely
clears the infection: West Nile virus continues to replicate at temperatures as high as 113 F (45 C).25 Most of the damage to the central nervous system is likely attributable to the inflammatory response, rather than West Nile
virus-induced cytopathology. Supportive care with fluid therapy, analgesics, and symptomatic treatments are the most important
aspects of patient management. Recumbent patients will require turning every few hours, and many animals incapacitated by
West Nile virus are appetent but unable to eat or drink without assistance. Antibiotics are unlikely to be beneficial if an
animal is indeed suffering from West Nile virus infection, but their administration may be prudent to address other differential
diagnoses and to help prevent nosocomial infection.
WEST NILE VIRUS IN BIRDS
Mortality from West Nile virus infection has been reported in a staggering number of bird species. Most data come from wild
birds, but zoos with outdoor aviaries have reported considerable losses, and some pet birds have also been afflicted.17,26 Avian infection with West Nile virus differs considerably from that in mammals and is highly variable among different species
of birds.8,19,26-29 Young hatchlings tend to rapidly succumb to West Nile virus infection, and some birds, particularly passerines, remain vulnerable
throughout their lives. The good news is that most domestic avian species, including psittacines, are relatively resistant
to severe clinical manifestations after infection with West Nile virus.8 Key points to consider:
- The clinical course of West Nile virus in birds is typically rapid. Initial lethargy and inappetence are followed by neurologic
signs (head tilt; torticollis; difficulty perching, drinking, and eating) and then agonal signs.
- All organ systems of birds may be infected with high levels of virus. Unlike mammals, birds showing clinical signs likely
have widespread, active viral infection.
- Some species of birds shed West Nile virus in saliva and excreta and may also spontaneously hemorrhage. These birds can infect
cage mates (in the absence of a mosquito vector) and also constitute a major zoonotic risk.
- Diagnosis can be made by PCR or virus isolation from serum and sometimes from oral or cloacal swabs.30
- If pursued, treatment is typically restricted to aggressive supportive care, with the use of proper precautions by handlers.
Corticosteroid therapy is generally regarded as being contraindicated since birds often have extensive, active infection.
However, corticosteroids may be beneficial during convalescence.
- Some clinically affected birds recover from West Nile virus infection. Those with neurologic signs may have prolonged convalescences
or permanent sequelae.
The efficacy of equine vaccines in preventing or even ameliorating disease from West Nile virus infection in birds is highly
questionable.31 Fortunately, few safety concerns have arisen. Work is currently under way to develop avian-specific vaccines, but none are
commercially available in the United States yet.
Laura Austgen, PhD, DVM
James L. Voss Veterinary Teaching Hospital
College of Veterinary Medicine and Biomedical Sciences
Colorado State University
Fort Collins, CO 80523