PORTLAND (AP) - Dogs displaced by Hurricane Katrina are bringing along a disease prevalent in the South but rare in Oregon - heartworm, which is spread by mosquitoes and is potentially fatal.

Veterinarians are urging dog owners to have their pets tested for heartworm before the mosquito season.

“We've got a window of opportunity, and if you love your pet, I'd give them preventive medicine for heartworm,” said Sharon Harmon, executive director for the Oregon Humane Society.

“My concern is there are animals coming in from the Gulf Coast via well-meaning volunteers who may not be treating them for heartworm before placing them in a new home,” she said.

Since the August hurricane, hundreds of dogs have come to Oregon through a variety of ways. The Humane Society, for example, brought about 150 dogs and cats, testing each for heartworm and other illnesses. About three of every four animals tested positive for heartworm, Harmon said, and each one was treated.

Heartworm is rare in most of Oregon, occurring in far less than 1 percent of the dogs living in the northern part of the state. The worms are spaghetti-like, making their way to the infected animal's heart. If untreated, the disease can lead to heart disease and death. To spread to other animals, the disease needs animals infected with heartworm and mosquitoes that can then transmit the parasite.

Preventing heartworm is cheaper than treating an infection, $15 to $40 for a blood test and $10 a month for prevention medicine. However, Harmon said, the treatment for a dog that contracts heartworm costs hundreds of dollars and can wind up costing as much as $2,500.