Avian influenza: An emerging feline threat? - Veterinary Medicine
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Avian influenza: An emerging feline threat?
Until recently, it was thought that cats couldn't get the flu. But the new strain of avian influenza ravaging birds in Asia can—and does—infect cats.


VETERINARY MEDICINE



Influenza in greyhounds: A cautionary tale
Domestic cats in Thailand have also been infected with the H5N1 virus.11,12 In February 2004, a group of 15 cats living near an affected poultry farm became ill. According to news reports, three of the cats had been tested for avian influenza by researchers at Thailand's Kasetsart University, with two cats having positive results at that time. Fourteen of the 15 cats had died, and the last cat was very ill. The method of influenza transmission in these cats was unknown.

A second outbreak of H5N1 avian influenza in nondomestic cats occurred in October 2004 in a tiger zoo in Thailand.13 Initially, the cats likely became infected by ingesting raw infected bird carcasses. Tigers infected later in the outbreak were probably infected by cat-to-cat transmission because they were fed cooked poultry beginning a few days after the first tigers became ill. Clinical signs in affected tigers included respiratory distress, a serosanguineous nasal discharge, neurologic signs, and high fever. Leukopenia, thrombocytopenia, and elevated liver enzyme activities were common laboratory findings. Most of the animals had severe lung congestion and hemorrhage. Infection with H5N1 avian influenza virus was confirmed in several animals by using immunohistochemistry, virus isolation, or both techniques. Twenty-nine tigers died during the first week of the outbreak, and a total of 147 of the zoo's 441 tigers either died or were euthanized during the three weeks after the first tigers became ill.

Experimental inoculation of domestic cats

In addition to these outbreaks, researchers have demonstrated the susceptibility of domestic cats to H5N1 avian influenza virus.14 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.

THE VETERINARIAN'S ROLE IN INFLUENZA SURVEILLANCE


Figure 2. Genetic reassortment of influenza viruses may lead to additional species being involved in transmission.
The H5N1 outbreaks in domestic and nondomestic cats in Thailand emphasize the potential of this virus as a feline pathogen. Although poultry and wild ducks are the primary reservoir of the virus, several species of songbirds are also susceptible to infection.15 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 2). Many influenza viruses can no longer legitimately be categorized as equine, avian, human, or swine viruses. It 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.


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Source: VETERINARY MEDICINE,
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