Experimental inoculation of domestic cats
In addition to these outbreaks, researchers have demonstrated the susceptibility of domestic cats to H5N1 avian influenza
virus.9 Unlike in previous studies with other influenza virus strains, cats developed severe respiratory disease after exposure
to H5N1 virus by ingestion, intratracheal inoculation, or contact with experimentally infected cats. Intratracheal inoculation
of three cats resulted in fever beginning Day 1 after exposure and in decreased activity, conjunctivitis, and labored breathing
by Day 2 after exposure. One cat died on Day 6. Pathologic findings included focal pulmonary consolidation and diffuse alveolar
damage. Two cats housed with these infected cats and three cats fed virus-infected chicks also developed similar clinical
signs and pathology. Infection with H5N1 avian influenza virus was confirmed in all these cats by virus isolation from pharyngeal
swabs and by immunohistochemistry on lung tissue.
Concerns over an H5N1 influenza pandemic
Although human cases have been sporadic to date and efficient human-to-human spread has not yet occurred, concerns about a
potential H5N1 influenza pandemic continue to rise. For the first time since the current H5N1 influenza outbreak began in
2003, migratory birds appear to be spreading the highly pathogenic avian influenza virus to domestic birds in countries along
their migratory routes. The virus has now been detected in birds in at least 32 countries.10 Despite this explosive spread in birds, little more than 200 human cases of H5N1 influenza have been confirmed during the
current outbreak; most of these cases can be traced to direct contact with sick or dead birds or their feces.
However, fears of an avian influenza pandemic remain because of the ability of influenza viruses to mutate and change or expand
their host range. Influenza viruses carry their genes on eight separate segments; infection of a single host cell with two
different influenza viruses can result in a new virus strain by packaging segments from both parent viruses in a single virus
particle (genetic reassortment). If such a reassortment resulted in enhanced transmission between people, a pandemic might
occur.10
The veterinarian's role in influenza surveillance
1. Genetic reassortment of influenza viruses may lead to additional species being involved in transmission.
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The H5N1 influenza outbreaks in domestic and nondomestic cats point to this virus's potential as a feline pathogen. Although
poultry and wild ducks are the virus's primary reservoir, several species of songbirds are also susceptible to infection.11 These bird populations could serve as a conduit of human infection through feline intermediaries. With each genetic reassortment
of the influenza viruses, species barriers become less effective (Figure 1). It therefore seems reasonable for veterinarians to consider including influenza as a differential diagnosis in cats with
respiratory and neurologic disease. Prompt recognition of avian influenza in any susceptible population of animals will help
control its spread and decrease the chance of another devastating influenza pandemic.
If you suspect avian influenza in any species, contact the Animal Health Diagnostic Center, College of Veterinary Medicine,
Cornell University (phone: 607-253-3900; e-mail: diagcenter@cornell.edu
) for testing information. Report cases of avian influenza to local or state public health departments or the county veterinarian.
Although guidelines for handling infected pets have not been established, human infection-control precautions recommended
by the Centers for Disease Control and Prevention can be adapted for use in companion animals. Use stringent hygienic care
(including using gloves, gowns, and masks) when handling potentially infected animals, and maintain these animals under isolation
conditions until testing is completed or for 14 days after the onset of clinical signs.
Treatment of influenza virus infection in cats would probably be based on supportive care. Influenza antiviral agents have
not been tested in cats, so their safety and efficacy are unknown. The use of antiviral drugs such as oseltamivir or zanamivir
in nonhuman species is discouraged because of concerns that circulating strains of influenza might develop resistance to these
drugs. In fact, the extralabel use of anti-influenza drugs in poultry has been banned by the FDA.12
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