The Ministry of Agriculture reported Friday that two out of 52 samples from sick dogs tested positive for swine flu, with the virus being similar to the one infecting humans.

Infectious disease specialist Lo Wing-lok said the virus' ability to transmit to dogs, cats and other animals will make the virus less likely to mutate.

"The more hosts that they can infect and survive on, the pressure for them to change or mutate will become considerably less, so the risk of mutation is becoming lower," Lo said.

"We can cause our pets to become sick, and our pets can cause us to become sick. Wash your hands and wear a mask if you are looking after sick dogs."

Chinese University associate dean of medicine Joseph Sung Jao-yiu said the risk of swine flu to humans will be great if highly mobile animals such as dogs and cats are infected.

A spokesman for the US-based International Society for Infectious Diseases said: "This adds another animal species to those already known to become infected by the influenza pandemic H1N1 virus. So far, pigs, turkeys, ferrets and cats have been reportedly infected."

He said those animals were most probably infected by humans.

Concern was also expressed over mainland reports of at least eight swine flu patients suffering brain damage.

David Hui Shu-cheong, a professor in respiratory medicine at Chinese University, said five children with swine flu in the United States and Britain are reported to have developed encephalitis. All survived.

As children have no immunity to the new flu, those below five are more prone to complications, Hui added.

Meanwhile, an obese 58-year-old man was reported to be critically ill at Caritas Medical Centre with swine flu. The man went to the hospital's accident and emergency department on Saturday suffering from chest infection and respiratory failure. He was immediately admitted to the intensive care unit and put on a respirator.

Test results for swine flu came back positive yesterday, and he was prescribed Tamiflu and antibiotics.