More cats found with bird flu
Researchers suggest feline 'sentinels' could identify dangerous outbreaks.
Domestic cats may be widely susceptible to infection with the avian flu H5N1 virus, according to scientists who this week reported the virus in two dead cats in northern Iraq. The latest reports, following recent cat cases in Austria, Germany, Thailand and Indonesia, reinforce the hypothesis that cats may play a role in the spread of the virus, although none of the human victims thus far is thought to have caught the virus from a cat.
The findings also suggest that cats might help provide an early-warning system for avian flu by acting as 'sentinels', say the scientists, who work at a US Naval Medical Research Unit in Cairo, Egypt. Many remote areas lack the veterinary infrastructure to test quickly for H5N1. So as a proxy, they argue, H5N1 should be immediately suspected and guarded against whenever unusual bird and cat die-offs happen together.
Bird flu continues to hit Asia. Thailand has just seen a resurgence in chicken cases this week, after being apparently free of the virus for a year.
H5N1 was first reported in domestic cats in Thailand in 2004, and a later survey showed that some Thai cats carry antibodies to the virus. Further lab work showed that cats can carry the virus in their guts and faeces, and so could contaminate the environment to spread the virus. "In nature we saw exactly what they saw in the lab," says Samuel Yingst, the lead author of the new work, speaking from Bishkek, Kyrgyzstan.
The researchers tested the cats out of curiosity during a two-week field trip last February near Erbil City, in Kurdish northern Iraq, after hearing anecdotal reports of cat deaths associated with H5N1 outbreaks in Turkey and Iraq the month before. Their findings are published in the August issue of Emerging Infectious Diseases1.
"It's conceivable that cats could spread the virus," says Yingst, although he suspects that they may be 'dead-end' hosts that die after receiving the disease without passing it on.
Dick Thompson, a spokesman for the World Health Organization (WHO), says the latest paper does not change the WHO's current position: "there is no present evidence that domestic cats play a role in the transmission cycle of H5N1 viruses. To date, no human case has been linked to exposure to a diseased cat."
That said, some cases of H5N1 continue to baffle scientists. There have been reports of cat die-offs in Indonesia in areas where no bird outbreaks have been reported, for example. And one cat virus has been shown to share gene sequences with human cases; gene sequences that have not been reported in poultry samples.
Some human cases from Java "have no obvious avian counterparts", concluded a dozen international experts in animal and human health at the Avian Influenza Expert Consultation meeting in Jakarta from 20-23 June. They said there is an "urgent need" to compare human, cat and bird sequences, but that such efforts are being hindered by a lack of data.
On the alert
In the meantime, the study could help spark an idea for early-alert systems. "Where cats show respiratory infections in areas where avian flu is endemic, H5N1 will probably be one of the causes," says Magdi Saad, a co-author on the work. Cats could therefore serve "as sentinels in areas which don't have access to good diagnostics", adds Yingst.
"I'd completely agree that cats can serve as sentinels, they seem very susceptible," says Albert Osterhaus, whose team at Erasmus University in Rotterdam, the Netherlands, has shown that experimentally infected cats can transmit the virus. Other carnivores are also likely to fall foul of flu, he says, adding that his group is now also looking at ferrets, foxes and seals.
Sentinels are important as a first alert, the experts agree, but they are no substitute for detailed investigation.
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- Yingst S. L., Saad M. D.& Felt S. A. . Emerg. Infect. Dis., http://www.cdc.gov/ncidod/EID/vol12no08/06-0264.htm (2006).