Leading flu researchers have warned that cats could be playing an unrecognised role in the spread of the H5N1 bird flu virus, and have criticised international organisations for ignoring this piece of the puzzle.
Writing today (6 April) in Nature, Thijs Kuiken, Albert Osterhaus and colleagues at the Erasmus Medical Centre in the Netherlands, and Peter Roeder of the UN Food and Agriculture Organization recommend ways to cut the chance of cats spreading H5N1 to people.
Domestic and wild cats used to be considered resistant to disease from influenza A type viruses, of which H5N1 is a subtype.
But since 2004, cats have increasingly been getting infected with H5N1 and falling ill (see Avian influenza: birds, pigs, now cats).
Recent reports suggest that H5N1 commonly infects domestic cats in countries such as Indonesia and Thailand, where the virus is well established in poultry.
But the researchers point out that cats died from H5N1 in Germany soon after the virus was found in wild birds there. This, they say, suggests that unusual cat deaths could be seen as an early warning that the virus has arrived in new areas.
They add that their own laboratory experiments show that cats can become infected with H5N1 after eating infected poultry or coming into close contact with other infected cats.
The researchers acknowledge that "major gaps in our knowledge remain," but conclude that, "the potential role of cats should be considered in official guidelines for controlling the spread of H5N1".
They criticise intergovernmental agencies for issuing "cautious statements" that overlook this possible role (see WHO and FAO issue advice on cats and bird flu).
In February, the World Health Organization stated that, "there is no present evidence that domestic cats play a role in the transmission cycle of H5N1 viruses".
And last month, the World Organisation for Animal Health (OIE) said that cases of H5N1 infection in cats "have not led to any change in the epidemiology of the disease".
The researchers say keeping domestic cats indoors could help control the spread of the virus, but admit that this would be difficult to enforce in developing countries.
They add that other domestic and wild carnivores, such as dogs and foxes, are likely to be vulnerable to H5N1 and to contribute to its spread, so should be monitored accordingly.