By Scott Line, Special for USA TODAY
Heartworm infection, once limited mostly to the South, is now being found in all 50 states, according to the American Heartworm Society, and the number of cases across the USA is on the rise.
Information from testing shows that more than 1 million dogs in the USA are infected with heartworms. Veterinarians in parts of the country where infection rates have been low, such as the Rocky Mountain states and the Pacific Northwest, are seeing an increasing number. Veterinarians in areas that have long had a high rate of the disease, including the Southern states and the Mississippi River Valley, are experiencing an even greater escalation.
Summer and early fall are peak seasons for mosquitoes, which can carry the threat. When an infected mosquito bites a dog, it can deposit immature heartworms that grow under the skin for about two months. The worms then migrate through the bloodstream to the heart and arteries in the lungs. After lodging in the lungs' blood vessels, these worms grow to up to 1 foot long. Heartworms can live for years, damaging the lining of the blood vessels that carry blood to the lungs and eventually leading to heart disease.
Signs of heartworm disease vary and can include coughing, tiring easily, difficulty breathing and fainting. Dogs that are more active are more likely to show such signs, and activity itself worsens the damage. Signs are often not detectable until the disease is well advanced.
Heartworms also can infect cats, causing severe inflammation in the lungs. But heartworm disease often is not recognized in cats because the infection is more difficult to diagnose than in dogs.
Pets that live indoors exclusively are also at risk of infection because mosquitoes that get into your house can transmit heartworms.
Left untreated, heartworm disease can be fatal.
Heartworm treatment — which is available only for dogs — can be risky for the dog and is expensive, sometimes as much as $1,000. That's why it makes sense to prevent heartworm disease.
The good news is that prevention is simple and inexpensive. A number of medications are available that can prevent heartworm disease. They do not prevent heartworm infection from mosquitoes; instead, they work by killing the immature heartworms migrating beneath the skin before they can reach the heart and blood vessels of the lungs.
Most heartworm products must be given monthly, and because dogs may get bitten by infected mosquitoes every day during peak mosquito season, giving the monthly preventives at the same time every month is important for their success.
Although you may think of heartworms as a summer problem, it's a disease that can be a risk to your pet at any time of year. A warm autumn extends the risk, and even a few days of warm weather in the winter can allow mosquitoes to become active. Because you can't predict when your pet will be at risk, experts recommend using heartworm preventives all year long.
Adult heartworms can be detected with a blood test, and experts recommend testing your dog every year to be sure it remains free of heartworms.
If your dog is found to have heartworms, early diagnosis and treatment can prevent serious consequences of heartworm infection.
Annual testing can help make sure this hasn't happened to your dog. See your veterinarian — and keep your pet healthy.