Human Infection
Previously there were no reports of disease in cats from infection with an influenza A virus. Kuiken says the evidence of transmission from cat to cat is a particularly important finding.
"With all of the human cases of H5N1 virus infection, the virus was transmitted from bird to human (bird to mammal), not from human to human (mammal to mammal)," Kuiken said. "Our study shows that H5N1 virus transmission from cat to cat (mammal to mammal) is possible."
The ability of the virus to infect cats suggests that cats could enable the pathogen to adapt to mammals. If the virus could replicate more easily in cats, it also might replicate more easily in humans, increasing the risk of a human influenza pandemic.
"That this H5N1 virus caused pneumonia and death in cats suggests that the virus has increased its ability to cause disease in this species—not that the species is less resistant," Kuiken said.
Risk Remote
Some scientists downplay the threat of the new findings.
"To be a significant new threat, the infection would have to keep the cat well enough to travel and spread and yet sick enough to maintain high doses of virus so that transmission is achieved," said Ian Jones, a professor at the School of Animal and Microbial Sciences at the University of Reading in England.
"This experimental situation shows this can occur. But it is a long way from the natural situation where a sick animal may hide away or die," he added. "So the real increase in risk may actually be quite small."
Michael Lai, a professor of molecular microbiology and immunology at the University of Southern California in Los Angeles, says the report should not scare people.
"It's true that the more animals the virus can infect, the more likely the virus can spread to humans," Lai said. "However, the possibilities that a cat serves as an additional reservoir for avian flu and that it may allow human and avian flu viruses to recombine are quite remote."
If the transmission occurred easily, Lai said, we should have seen widespread flu infection in cats in the avian flu epidemic areas in the past few years. This did not happen.
The study authors also tested the effect of another type of influenza virus, H3N2, which most commonly causes flu in humans. Cats exposed in the same way to this virus did not develop disease.
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