Summer is the perfect season for enjoying the outdoors with your pets, but be careful: it’s also the time of year where dogs are more susceptible to heartworm because of mosquito bites.

It’s estimated that one million dogs will become heartworm positive in the United States every year, and according to the Companion Animal Parasite Council, that risk may be even more pronounced in 2016, especially in the lower Mississippi River region, eastern Missouri, southern Illinois, and southern Indiana.

Heartworm is a fully preventable condition wherein parasites transmitted by mosquito bites can develop into foot-long worms that live in an animal’s heart, lungs, and blood vessels, causing potential lung disease, organ damage, heart failure, and death. The worms can grow and develop offspring, which might afflict a dog’s entire system even though symptoms may not be visible for a year or more.

Veterinarians across the country urge that prevention is the best way to fend off infection. Pets should be tested annually and given medication every month, especially in mosquito-prone areas.

“Heartworms are actually transmitted by mosquitoes, so in Florida, you know we get a lot more mosquitoes in the summer, so we do see an increase in the number of cases of heartworms that come into our shelter over the summer,” said Humane Society executive director Stacey Hannouche of Pinellas County, FL.

Even if your dog does become infected, there are treatment courses available. “We can treat these animals and have them live a long, healthy life,” explained Sarah Brown, animal chief services at the Humane Society of Manatee County, FL. “It’s not something that is wrong. It is just something that we need to treat. Prevention is not that expensive.”

More veterinary services are offering low-cost prevention, treatment, and education programs in an effort to eradicate heartworm for good. While the disease used to signal a death knoll for dogs, that’s not the case anymore.

Amanda Audia, for example, adopted her dog Segar knowing he had heartworm. After a six-month treatment course, he was back on his feet.

“He’s been on prevention ever since and now he’s 9 years old,” said Audia. “Doesn’t have any symptoms from it. It’s all cleared up and he’s a happy and healthy guy.”