At the turn of spring and summer, it is the season of influenza outbreaks. The weather is hot and cold, which catches people off guard. In addition, the air is humid and the temperature is suitable, which is also easy to breed bacteria and viruses. Dog flu is a very troublesome thing. The mortality rate for dogs is very high, so how do we know if a dog has the flu?

A new strain of influenza from Asia is sickening dogs in the American Midwest, experts say.

Samples collected and tested by experts show that this new dog influenza virus has never appeared in the United States before. More than 1,000 dogs have now been infected with the virus in Illinois, Wisconsin, Ohio and Indiana, and six have died.

"Canines have never been stressed like this before," said Dr. Keith Paulson, a veterinarian and professor at the University of Wisconsin-Madison.

This canine disease exhibits flu-like symptoms in humans, such as cough, runny nose, fever and loss of appetite. A small percentage of dogs are carriers of the virus but do not show symptoms.

The virus may be spread through nose-to-nose contact, which may occur in foster care centers, veterinary clinics and parks.

The virus has not appeared to infect humans, Dr. Paulson said. Although the possibility of human-dog transmission has not been ruled out, he believes that the probability is very low. Although there have been no reports of virus-positive cats, there have been reports of cats becoming ill after direct contact with dogs.

Dr. Paulson also explains how to prevent more dogs from getting sick. If you take your dog to the park, please keep it on a leash and avoid places where there are lots of dogs, especially puppies and old dogs, who have very weak immune systems. Likewise, if your dog is sick, don't take him around.

The virus has an incubation period of 1 to 3 days and can persist in infected animals for up to 14 days. Symptoms usually last 5 to 7 days, and the cough can last up to several weeks.

This new virus is different from the previous dog influenza virus H3N8. H3N8 has been spreading across the United States since 2004. The virus, called H3N2, has been found in China and South Korea, and sick animals may have been brought into Chicago.

The vaccine is usually against the previous dog flu in the United States, but is only given to dogs who live in high-risk environments. And experts don't know whether the vaccine will be effective against the new virus. Some pharmaceutical companies have begun developing new vaccines, but it may take four to six months before they are ready for use.