Reports from Germany of a cat found dead due to a highly pathogenic avian influenza virus infection have fueled concerns about the risk this emerging virus poses to cats and, subsequently, to the people who care for them. Can cats catch the bird flu? These reports, along with recent studies, say "yes." But might it also be possible for cats to get the flu from us- or for humans to get the flu from cats? The short answer is "no." None of the known strains of influenza virus are transmissible between cats and people. But these viruses are very changeable by nature, so the long answer is a bit more complex.
Of the three types of influenza viruses- A, B, and C-type A viruses have the most significant implications for human and animal health. There are many subtypes and countless strains of influenza A viruses, but all of them can infect birds (wild waterfowl and migrating birds are the natural hosts), so they're commonly called avian influenza viruses. These viruses vary tremendously in their ability to cause disease; some subtypes and strains even jump species and infect other animals, including humans.
Although infected wild birds don't usually get sick themselves, they can spread these viruses to domestic fowl, with devastating consequences. One highly pathogenic avian influenza virus (the H5N1 subtype) has been spreading from Asia to Europe and Africa, most likely through wild bird migrations. This virus has resulted in the deaths of approximately 200 million domestic commercial birds to date, due to either direct infection, or the culling of flocks done to keep infection from spreading. Some humans have become infected with H5N1, and a high percentage of them have died as a result. It's believed that most, if not all, of these people became infected by direct contact with infected birds. According to the World Health Organization, "All available evidence indicates that the virus does not spread easily from poultry to humans.Almost all cases have been linked to close contact with diseased household flocks."
Health officials in the U.S. carefully monitor avian influenza outbreaks in domestic fowl flocks, partly due to concerns that viruses that don't often cause disease in birds-so-called low-pathogenic viruses-might evolve into highly pathogenic, rapidly spreading forms that would necessitate the destruction of entire flocks. Such losses, along with resultant trade restrictions, would have a tremendous economic impact on the poultry industry. But monitoring is also important because of the possibility that a particular avian influenza virus could directly infect people-or evolve into an even more dangerous virus by genetically mixing with ordinary human influenza viruses.
What about Cats?
Several studies have investigated cats. The first, "Avian Influenza H5N1 in Tigers and Leopards" (Emerging Infectious Diseases, Vol. 10, No. 2), reported on exotic cats becoming infected by eating H5N1-infected chickens obtained from a local slaughterhouse. A second report, "Avian H5N1 Influenza in Cats" (Science, Vol. 306, Issue 5694), showed that domestic cats, too, can be infected if fed uncooked meat from H5N1-infected chickens. Perhaps even more disturbing, this latter study showed that infected domestic cats were capable of spreading infection directly to other cats. A third report, "Influenza A Virus (H5N1) Infection in Cats Causes Systemic Disease with Potential Novel Routes of Virus Spread within and between Hosts" (American Journal of Pathology, Vol. 168, No. 1), published in January 2006, more fully described the disease in cats. It further confirmed that domestic cats can be infected by eating infected birds, and that infected cats can spread infection to other cats, most likely through feces, urine, and secretions from the respiratory tract. As noted before, there is currently no evidence that influenza-infected cats can in turn infect humans.
The German cat mentioned earlier is believed to have eaten one of the H5N1-infected wild birds recently found in the same part of the country. At the time of this writing, the H5N1 virus is not present in North America. If H5N1 or an equally harmful influenza virus were to appear, the safeguards established by governmental agencies should help prevent the kinds of outbreaks that have occurred in other parts of the world. For these reasons, the risk to cats in this country is considered very low.
Two additional safeguards can reduce the already-low risk of feline infection. First, don't feed uncooked poultry to cats. Since the H5N1 virus is destroyed at 70º C, the high temperatures required to manufacture commercial cat foods eliminates the risk of infection in cats exclusively fed these foods. Second, keep cats indoors to prevent them from eating infected birds; because cat-to-cat infection is possible, this measure has the added advantage of preventing exposure to potentially infected outdoor cats.
Dr. James Richards
Director, Cornell Feline Health Center
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