The H1N1 flu which has hit millions of people worldwide has already infected cats and ferrets, but scientists cannot rule out other species being affected.
"A small number of companion animal H1N1 flu cases have been confirmed in the United States," said Dick Hesse, a flu expert and director of virology in Kansas State University's Veterinary Diagnostic Laboratory.
"The pets appear to have become ill after being in close contact with their owners and caretakers who were sick with H1N1. There is no evidence of pets passing H1N1 to people at this time."
Hesse said that because this strain of H1N1 is new, information about how it impacts animals is limited. It is possible that any animal may be susceptible to H1N1, but no other cases have yet been documented in companion animals other than cats and ferrets.
Dogs and pet birds have been susceptible to other strains of flu.
Among livestock, testing has confirmed the H1N1 virus in pigs, and horses can also contract certain strains of flu.
The testing of pets for H1N1 is part of the US Department of Agriculture's National Animal Health Laboratory Network, said Gary Anderson, director of the university's Veterinary Diagnostic Laboratory. The lab is testing samples submitted by veterinarians for H1N1 diagnosis.
"The National Animal Health Laboratory Network is using a test initially developed to detect H1N1 in pigs, which has now been approved for companion animal testing," Anderson said. "Tests will be performed on nasal or oral swabs, which should be obtained by a veterinarian and submitted to the lab for testing."
Anderson suggests pet owners see their veterinarian about keeping their pets healthy this flu season.
"Although rare, transmission of influenza viruses from people to dogs and cats can occur," said Ken Harkin, associate professor of small animal internal medicine.
"This is true with both H1N1 as well as H3N2, but the magnitude of the H1N1 pandemic dramatically increases the pet population exposure to influenza virus.
"We don't think the pet owner should be overly concerned. However, if pet owners are infected with H1N1 they should notify their veterinarian immediately if the pet becomes ill."