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NOTE FROM T J Dunn, DVM...
The information on this page is taken from the Centers For Disease Control and Prevention from the page titled West Nile Virus and Dogs and Cats and from the Avian Influenza page. Go to www.cdc.gov for a vast library of animal and human disease topics.

Most dogs and cats spend at least some time out of doors and thus risk exposure from blood sucking insect vectors. Also, as carnivores, dogs and cats may be exposed to WNV through ingestion of infected small mammals and birds, which are known to have large quantities of WNV in blood and tissue during the course of infection. Since there are an estimated 68 million companion dogs and 73 million pet cats in the United States alone, evaluating their response to WNV infection, assessing their potential to serve as amplifying hosts for this virus, and obtaining some estimate of the clinical consequences of infection are important concerns.

There are three types of influenza viruses: A, B, and C. Only influenza A viruses are further classified by subtype on the basis of the two main surface glycoproteins called hemagglutinin (HA) and neuraminidase (NA). Influenza A subtypes and B viruses are further classified by strains. Human Influenza Viruses and Avian Influenza A Viruses. Humans can be infected with influenza types A, B, and C viruses. Subtypes of influenza A that are currently circulating among people worldwide include H1N1, H1N2, and H3N2 viruses. Wild birds are the natural host for all known subtypes of influenza A viruses. Typically, wild birds do not become sick when they are infected with avian influenza A viruses. However, domestic poultry, such as turkeys and chickens, can become very sick and die from avian influenza, and some avian influenza A viruses also can cause serious disease and death in wild birds.
(*  Birds from 32 countries have been identified as being infected with the H5N1 strain as of 7/2006. Dr.Dunn)

Can domestic cats be infected with avian influenza viruses?
While domestic cats are not usually susceptible to influenza type A infection, it is known that they can become infected and die (both experimentally and naturally) with avian influenza A (H5N1) viruses and, in a laboratory/research setting can spread the virus to other cats. It is not known whether domestic cats can spread the virus to other domestic cats under natural conditions.
 

Q. Can West Nile virus (WNV) cause illness in dogs or cats?
A. A relatively small number of WNV infected dogs (<40) and only 1 WNV infected cat have been reported to CDC during 2003. Experimentally infected dogs* showed no symptoms after infection with WNV. Some infected cats exhibited mild, nonspecific symptoms during the first week after infection--for the most part only showing a slight fever and slight lethargy. It is unlikely that most pet owners would notice any unusual symptoms or behavior in cats or dogs that become infected with WNV.

Q. How can my veterinarian treat my cat or dog if they are/may be infected with WNV?
A. There is no specific treatment for WNV infection. Full recovery from the infection is likely. Treatment would be supportive (managing symptoms, if present) and consistent with standard veterinary practices for animals infected with a viral agent.

Q. Does my dog/cat becoming infected pose a risk to the health of my family or other animals?
A. There is no documented evidence of dog or cat-to-person transmission of West Nile virus. The evidence suggests that dogs do not develop enough virus in their bloodstream to infect more mosquitoes. Cats develop slightly higher levels of virus in their bloodstream, but it is unclear if this would be enough to infect mosquitoes. It is very unlikely that cats would be important in furthering the spread of the virus. *

If your animal becomes infected with WNV, this suggests that there are infected mosquitoes in your area. You should take measures to prevent mosquitoes from biting you (use repellent and wear protective clothing.)

From the Wisconsin Veterinary Medical Association website:

West Nile viral encephalitis is a mosquito-borne infection of the brain caused by the West Nile virus. West Nile virus is spread by the bite of an infected mosquito, and can infect people and animals. Wild birds, horses, and humans are the species most often affected; however, the virus has also been identified in cats, dogs, bats, chipmunks, skunks, squirrels and domestic rabbits. Although these latter species may become infected, they usually do not develop clinical signs of disease.

Risk of contracting West Nile virus is low. In areas where mosquitoes carry the virus, less than one percent are actually infected. Even if mosquitoes are infected, less than one percent of people bitten and infected become severely ill.

Most infections in humans are relatively mild, with flu-like symptoms including fever, headache, body aches and, in some cases, skin rash and swollen lymph glands. Signs of more severe infections include high fever, neck stiffness, muscular weakness, convulsions and paralysis. Death rates associated with severe infection range from three to fifteen percent and are highest among the elderly.

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Dogs, cats and their people are continually moving into wider and more diverse environments.  This results in exposure to "new" diseases and disease carriers.  Look at LYME disease in dogs as a classic example of a well established "new and emerging" disease of man and animals.

Learn more about ThePetCheckup™

How do cats become infected with avian influenza A (H5N1) viruses?
All of the cases of influenza A (H5N1) infection in domestic cats reported to date have been associated with H5N1 outbreaks among domestic poultry or wild birds and are thought to have occurred by the cat eating raw infected birds.

How commonly have cats been infected with avian influenza A (H5N1) viruses?
During the avian influenza A (H5N1) outbreak that occurred from 2003 to 2004 in Asia, there were only several unofficial reports of fatal infections in domestic cats. Studies carried out in the Netherlands and published in 2004 showed that housecats could be infected with avian influenza A (H5N1) and could spread the virus to other housecats. In these experiments, the cats became sick after direct inoculation of virus isolated from a fatal human case, and following the feeding of infected raw chicken. In February 2006, Germany reported that a domestic cat had died from influenza A (H5N1) infection. That cat lived in the northern island of Ruegen, where more than 100 wild birds are believed to have died of the disease. The cat probably got sick by eating an infected bird.

What about infection in large cats, like tigers?
Large cats kept in captivity have been diagnosed with avian influenza as well. In December 2003, two tigers and two leopards that were fed fresh chicken carcasses from a local slaughterhouse died at a zoo in Thailand. An investigation identified avian influenza A (H5N1) in tissue samples. In February and March 2004, the virus was detected in a clouded leopard and white tiger, respectively, both of which died in a zoo near Bangkok . In October 2004, 147 of 441 captive tigers in a zoo in Thailand died or were euthanatized as a result of infection after being fed fresh chicken carcasses. The cats are thought to have gotten sick from eating infected raw meat. Results of a subsequent investigation suggested that at least some tiger-to-tiger transmission occurred in that facility.

Can cats spread H5N1 to people?
There is no evidence to date that cats can spread H5N1 to humans. No cases of avian influenza in humans have been linked to exposure to sick cats, and no outbreaks among populations of cats have been reported. All of the influenza A (H5N1) infections in cats reported to date appear to have been associated with outbreaks in domestic or wild birds and acquired through ingestion of raw meat from an infected bird.

What is the risk to humans or other species from cats infected with avian influenza H5N1 virus?
There is no evidence to date that cats can spread H5N1 to humans. No cases of avian influenza in humans have been linked to exposure to sick cats, and no outbreaks among populations of cats have been reported. All of the influenza A (H5N1) infections in cats reported to date appear to have been associated with outbreaks in domestic or wild birds and acquired through ingestion of raw infected meat.

What is the current risk that a cat in the United States will become infected with influenza A (H5N1)?
As long as there is no influenza A (H5N1) in the United States, there is no risk of a U.S. cat becoming infected with this disease. The virus circulating in Asia, Europe and Africa has not yet entered the United States. CDC is working closely with domestic and international partners to continually monitor this situation and will provide additional information to the public as it becomes available.

If avian influenza A (H5N1) is identified in the United States, how can I protect my cat?
As long as there is no H5N1 influenza in the United States, at this time there is no risk of a U.S. cat becoming infected with this disease. In Europe, however, where H5N1 has been reported in wild birds, poultry, several cats, and a stone marten (a member of the weasel family), the European Center for Disease Prevention and Control has issued preliminary recommendations for cat owners living in H5N1-affected areas. Additionally, the Food and Agriculture Organization has produced guidance for areas where H5N1 HPAI has been diagnosed or is suspected in poultry or wild birds.

Where can I find out more information about avian influenza infection in cats?
For more information about avian influenza in cats, see Avian influenza — Frequently asked questions (from the American Veterinary Medical Association) and H5N1 in Cats (from the Food and Agriculture Organization of the United Nations).

Cans dogs be infected with avian influenza?
While dogs are not usually susceptible to avian influenza viruses, the avian influenza A (H5N1) virus that emerged in Asia in 2003 has been documented to infect other carnivore species (e.g. cats, tigers, leopards, stone martens). This has raised concern that this strain of avian influenza A (H5N1) virus may be capable of infecting dogs. An unpublished study carried out in 2005 by the National Institute of Animal Health in Bangkok indicated that dogs could be infected with the virus, but no associated disease was detected. This limited information is not enough to determine definitively whether dogs are susceptible to the virus. CDC is coordinating with USDA, veterinary associations, and other partners domestically and internationally on this issue and will provide additional information to the public as it becomes available.

How would dogs be infected with avian influenza A (H5N1)?
There is not enough information available about avian influenza A (H5N1) infection in dogs to know how infection would occur. Affected domestic cats in Europe appear to have become infected by feeding upon raw infected poultry or wild birds. If dogs are susceptible to avian influenza A (H5N1), infection may be by the same route.

What is the current risk that a dog in the United States will become infected with avian influenza A (H5N1)?
As long as there is no influenza A (H5N1) in the United States, there is no risk of a U.S. dog becoming infected with this disease. The virus circulating in Asia, Europe and Africa has not yet entered the United States. CDC is working closely with domestic and international partners to continually monitor this situation and will provide additional information to the public as it becomes available.

Visit The Centers For Disease Control and Prevention at CDC.gov