The emergence and spread of the H5N1 strains of avian influenza in recent years has caused concern over a future pandemic
in the human population. The virus, a particularly virulent and contagious strain, has affected waterfowl and domestic poultry
in Asia, Europe, the Middle East and Africa. In addition, it has successfully infected humans in contact with infected birds,
leading to severe disease, and death in over 50% of cases. Thusfar, efficient human-to-human spread has not occurred.
Infection has also occurred in domestic cats and dogs. Seropositive dogs and cats have been found in Thai villages. Natural
infection of dogs has occurred from ingestion of infected carcasses. In some cases, systemic disease and death have occurred.
Cats also may be infected by consumption of carcasses of infected birds. During an outbreak in Germany among waterfowl, infection
of several domestic cats occurred. Infections were fatal, and pneumonia and hepatic necrosis was found. Experimental studies
in cats have produced lethal infections, and spread to in-contact cats. Shedding was documented in both respiratory secretions
and feces of infected cats. Inoculation studies in dogs have shown susceptibility of dogs to infection with H5N1, and shedding
may occur from the nose with no signs of disease. This study also showed receptors for the avian influenza exist in both the
upper and lower respiratory tracts of dogs.
Because these animals live in close contact with humans, concern exists over the risk of transmission from these animals.
This possibility also brings questions from owners regarding risks to their pets, and themselves. Currently, it is unlikely
that cats and dogs play any role in the natural transmission of avian influenza. No direct transmission has been reported,
and the level of shedding by these animals appears to be lower than that of birds. However, monitoring of domestic pets during
an H5N1 outbreak is warranted.
Rabies virus continues to be a threat to domestic pets worldwide. Recently, it was announced by the CDC that the canine strain
of rabies has been eliminated from the US. However, the virus remains present in wildlife in the US, posing a risk for domestic
pets, as well as people. Lyssaviruses continue to emerge in other parts of the world, and genetic variants of rabies virus
do exist. New variants of rabies virus in North America could occur and pose an emerging threat. Rabies infections in raccoons
are of particular concern due to the increased likelihood of raccoon contact with pets as well as people in suburban areas.
In addition, importation of dogs poses a risk for introduction of foreign variants. Data indicates an increasing number of
unvaccinated puppies are being imported into the US, and since 2004, infection has been documented in at least two imported
puppies. Federal regulations are under review to address these risks.
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