By Carrie Reeves

MISSISSIPPI STATE -- Mississippians consider mosquitoes a nuisance during the summer months, but to their pets, these swarming pests can be deadly.

Heartworms are a life-threatening disease that affect dogs and cats, although they are most common in dogs. The disease is caused by the presence of the adult stage of the parasite Dirofilaria immitis.

"Heartworms are a parasite spread by mosquitoes that take up residence in the pulmonary artery and the right ventricle of an animal's heart," said Dr. Mark Stickney, assistant clinical professor at Mississippi State University's College of Veterinary Medicine.

The more mosquitoes in an area, the greater the risk of a pet developing this disease. Spread of the disease is limited to warm months as the immature worms go through a period of development inside the mosquito. It takes about two weeks with temperatures at or above 70 degrees to complete this stage.

"Any dog that is in an area with mosquitoes may get bitten and develop the disease," Stickney said. "The worms will finish development inside the animal's heart."

An infected mosquito bites a dog, releasing immature heartworms into the dog's body. The worms mature in the dog's heart about six months after the initial bite. Adults mate and live in the pulmonary arteries and the right ventricle of the heart where they can survive up to seven years.

"The worms take up space in the animal's heart so that the heart is not physically able to pump enough blood to keep the animal alive," Stickney said.

Symptoms of heartworms develop slowly, and often symptoms are not noticed for up to three years after the initial bite. Most problems are due to the increased workload of the heart caused by blockage by the heartworms. Lack of energy and inability to exercise are early symptoms, as well as chronic coughing and difficulty breathing.

Increased blood pressure from the blockages places a strain on the right ventricle of the heart. As the disease progresses, most dogs develop congestive heart failure and often collapse in the final stages of the disease.

"The animal will show signs of lethargy, weakness and a loss of appetite," Stickney said. "The blockage in the heart causes the animal to eventually go into heart failure. Their heart is full of worms."

Stickney recommended that dogs receive preventative for heartworms on a regular basis. Several methods of prevention are 100 percent effective. Once a month oral treatments, such as Heartguard and Interceptor, and topicals, such as Revolution, are recommended for prevention of heartworms.

"All of these treatments are proven effective if given as directed," Stickney said. "Because of Mississippi's climate and mosquito population, I recommend that people treat animals year round to prevent this disease."

Have veterinarians test dogs for heartworms regularly and treat immediately if they test positive. Veterinarians can treat most dogs with heartworms successfully with injections.

For more information, contact: Dr. Mark Stickney, (662) 325-1250