Domestic cats can carry the SARS virus and transmit it to other cats -- and perhaps to humans, new research has found.
The researchers say public health officials would need to consider cats as part of their quarantine plan if there was another outbreak of severe acute respiratory syndrome in Canada or elsewhere in the world. But they caution that cat owners should not get rid of their pets for fear of SARS.
"In principle, for quarantine, you should consider cats. What you would like to prevent is people throwing their cats out on the street," Albert Osterhaus, with the Institute of Virology at the Erasmus Medical Centre in the Netherlands, said in an interview.
He and his colleagues reported in today's edition of the British journal Nature that they were able to infect cats and ferrets with the SARS virus by putting drops containing the virus into their eyes, noses and throats. They also revealed, for the first time, that when 100 people were infected at the Amoy Gardens apartment block in Hong Kong, cats were not immune. Hong Kong researcher Wilina Lim found that at least two cats in the complex had been infected with the virus that causes SARS in humans. It is not clear if they played a role in the widespread infection that occurred in the now infamous apartment building.
Allison McGeer, head of infection control at Toronto's Mount Sinai Hospital, says she's not sure quarantining cats would be necessary should there be another outbreak of SARS.
"We controlled the outbreak without paying any attention to animals," she said in an interview. "Cats weren't important this year."
But that could change.
Most corona viruses attack a specific host, not a wide range of animals. The new findings show that the SARS virus can affect a far wider range of animals than previously believed.
This increases the chances that more humans will be infected. It also increases the risk that the virus may mutate in one of its many hosts, and that new version may emerge. This is a possibility that worries Dr. McGeer.
Earlier studies have shown that wild animals such as Chinese ferret badgers, masked palm civets and raccoon dogs have been infected with a virus very similar to the one that causes SARS in humans.
Scientists believe that the SARS virus jumped to humans from one of these exotic creatures at a live-animal market in Guangdong, China.
Dr. McGeer said that if there were to be another outbreak, she and other infection-control experts would have to assess the role that cats or other animals might be playing in the chain of transmission.
But it will hard to get an answer to the crucial question of whether cats can infect humans. It would be unethical to conduct experiments. In the event of another outbreak, researchers would have to consider it as a possibility.
Dr. Osterhaus and his team were able to easily infect six domestic cats and six ferrets with virus from a human SARS patient.
The cats didn't show any symptoms, but three of the ferrets became lethargic two to four days after being infected and one of them died. When autopsies were carried out, the cats were found to have mild versions of pulmonary lesions similar to those seen in monkeys infected with the SARS virus.
All the animals harboured growing amounts of the virus for six to eight days after infection. They were also shedding the virus for up to 14 days after they were infected, and infected animals quickly passed the virus to other animals they were housed with.
Dr. Osterhaus said hygiene may play a role in how quickly the virus spreads from humans to cats. At the Amoy hotel, for example, a leaky sewage system may have helped spread the virus.