Sep 3, 2004 (CIDRAP News) – House cats can acquire H5N1 avian influenza and pass it on to other cats, Dutch researchers reported this week.

Last February two cats in Thailand reportedly died of H5N1 avian flu, but yesterday"e;s article in the online edition of Science apparently is the first report of cats being experimentally infected with the virus and then spreading it to other cats.

Researchers sprayed H5N1 virus into the throats of three cats, according to the report by Thijs Kuiken and colleagues from Erasmus Medical Center in Rotterdam, Netherlands. The virus sample had been isolated from a Vietnamese person who died of the disease.

The cats had a fever just 1 day after being exposed to the virus and were excreting virus after 3 days, though in relatively low amounts, the report says. One cat died 6 days after exposure.

Two other cats were put in contact with the first group 2 days after the latter had been infected. In addition, the researchers fed infected chicks to three more cats. All of the additional cats became ill with signs like those of the first group.

Three other cats were exposed to influenza A (H3N2), a common human strain, and stayed healthy.

After the infected cats were euthanized, necropsy showed they had diffuse alveolar damage like that caused by H5N1 infection in humans and monkeys, the report says.

The findings suggest that "the role of cats in the spread of H5N1 virus between poultry farms, and from poultry to humans, needs to be re-assessed," the researchers write. In addition, "Cats may form an opportunity for this avian virus to adapt to mammals, thereby increasing the risk of a human influenza pandemic."

The Dutch report comes about 2 weeks after a Chinese expert on avian flu, Chen Hualan, reported that H5N1 virus had been detected in some pigs in China. The report triggered widespread concern because pigs can harbor human as well as avian flu viruses, creating the potential for the viruses to combine and form a new strain that could spark a human flu pandemic.

When H5N1 infection was reported in cats in Thailand last February, the World Health Organization (WHO) said cats had not previously been considered naturally susceptible to flu viruses. At the time, the agency said that pigs, seals, whales, mink, and ferrets were the only mammals besides humans considered susceptible to avian flu viruses. The WHO said only pigs could harbor both avian and human flu strains.

Other reports of H5N1 infections in mammals this year included cases last February in a leopard and a tiger in a zoo in Bangkok, Thailand.

Kuiken T, Rimmelzwaan G, van Riel D, et al. Avian H5N1 influenza in cats. Science 2004;Sep 2 (early online edition) [Abstract]