Dogs love without condition. Dogs warm our hearts and our beds. We spend time to train them and money to keep them healthy. The thought of a new highly contagious disease threatening their lives is heartbreaking. So far, the H3N2 strain of dog flu has reached 25 states since last spring, forcing several shelters to shut down and sickening thousands of dogs.

Here's what you need to know about the newest strain of dog flu called H3N2:

  • The dog flu spreads the same way human flu does, from a sneeze or cough, or by touching contaminated surfaces. The virus can live on these surfaces for about two days.
  • Dogs are at risk who spend time in places like doggie day care, dog parks or vet clinics.
  • Some common symptoms of dog flu are high fever, cough, runny nose, watery eyes, sore throat and loss of appetite. Dogs with the flu usually show symptoms for about two weeks.
  • Dog owners should watch for changes in behavior, eating and drinking habits, and labored or rapid breathing. Take the dogs temperature if you notice symptoms.

According to

The highly contagious illness, also called canine influenza, appears to have begun spreading last spring in the Chicago area and sickened more than 1,000 dogs in the Midwest. Although most dogs recover, a handful of deaths were reported. It has since spread to about 25 states.

"It kind of stunned most of us in the veterinary community because it spread like wildfire," veterinarian Dr. Ernie Ward told CBS News when the first wave of the outbreak was raging last April.

Experts say this strain of the virus, called H3N2, was first seen in Asia but only recently appeared in the U.S., meaning dogs in this country are highly vulnerable. "None of the dogs have immunity to fight it off, so you see large numbers of dogs getting ill when the virus starts to circulate," Dr. Beth Lipton, veterinarian for Public Health Seattle and King County, told CBS News.