It seems like we hear about new diseases carried by mosquitoes all the time, but it is very important not to forget one of the most serious mosquito-transmitted diseases affecting our canine friends: heartworm.

Heartworm can cause serious and life-threatening complications, and all dogs should be treated monthly with a preventative.

The heartworm is an actual worm that can grow to be 12 inches or longer. Heartworms live primarily in the blood vessels that carry blood to the lungs. In severe cases, these worms can even infest the heart itself and can cause high blood pressure, difficulty breathing and, eventually, death due to heart failure.

Luckily, heartworms are not contagious to people and are not transmitted directly from dog to dog. They are transmitted between animals by bites from infected host mosquitoes. Pets are usually most susceptible to these bites in the spring after an area has experienced a few weeks of warm weather. But after warm winters, such as the one we had this year, and in some parts of the country where there is no deep freeze in the winter, heartworm can be a threat year-round.

Once introduced into the body, the immature worms can spend up to five months maturing in the dog’s body before migrating to the vessels that carry oxygen to the heart. While the worms are maturing, heartworm tests will be negative. Once the maturation process is complete, the larvae migrate to the pulmonary artery where they grow into mature worms. These mature worms release more immature worms into the bloodstream, starting a new lifecycle.

Signs of heartworm can include coughing, fainting, and difficulty breathing. The infected animal may also be easily fatigued. Unfortunately, animals may have heartworm for several years before signs of the disease appear. When symptoms finally do present, the heart and pulmonary arteries are often so full of worms that treatment is very risky and can sometimes result in fatal side effects.

What can you do to prevent it? Without a doubt, the easiest way to ensure the health of your dog is to prevent infection from the start. Your veterinarian will test your dog annually for heartworm, provide preventative, and may recommend that you keep your dog on preventative year-round. Heartworm preventatives are a once-a-month tablet or chew that often also protects against other intestinal parasites as well. Although these preventatives cannot treat heartworms once they are present, they can prevent your dog from getting them in the first place. Be sure you test your dog for heartworm every year and place him or her on a good preventative to keep his or her heart in great shape.

— Jennifer Stone is the medical director and staff veterinarian at the Lawrence Humane Society.