DrFitchWithDogSpring is around the corner and with it comes warm weather, sunshine, long walks outdoors…and mosquitoes. Heartworm disease can be fatal and pet parents need to know what it is and how to prevent it!

What is heartworm disease?
Heartworm disease is caused by a parasite called dirofilaria immitis. The adult worms, which can be up to a foot long, live in the heart, lungs and associated vessels of pet dogs and sometimes cats. Serious, potentially fatal consequences include severe lung disease, heart failure and damage to other organs such as the liver or kidneys. Mosquitoes serve as a carrier in the transmission of heartworm disease from one animal to another.

Symptoms of heartworm disease in dogs can vary from mild or no symptoms in early stages to life-threatening cardiovascular collapse as large numbers of worms can cause sudden blockage of blood flow in the heart. Common symptoms include mild persistent cough, exercise intolerance and fatigue after moderate exercise, decreased appetite and weight loss. In late stages, dogs can develop heart failure with fluid accumulating in the abdomen.

Symptoms in cats often include asthma-like cough, periodic vomiting, decreased appetite and weight loss. In some cats the first symptoms are sudden collapse or death.

Who is at risk?
Heartworm disease commonly affects pet dogs, cats and ferrets but heartworms can also be found in wild mammals such as coyotes, foxes, sea lions and even on rare occasions, humans. Heartworm disease has been reported in all 50 states as well as in countries around the world. Over 3,500 cases of heartworm disease have been reported in Massachusetts over the past five years according to Idexx Laboratories. For some southern states, the numbers top 20,000 cases over the same time period. The prevalence of adoptions from southern states means more potentially infected dogs are moving into the Northeast. Colder winters in the Northeast do not make those states immune to heartworm disease. Mosquitoes can overwinter indoors, and some species are becoming more cold-tolerant. Both indoor and outdoor pets are at risk.

How can heartworm disease be prevented?
Thankfully, there are medications we can use to prevent heartworm disease in our pet dogs and cats. These medications come in the form of oral pills or topical spot-ons that are given monthly or an injection for dogs given every six months. Oral and some spot-on products have the added benefit of preventing intestinal parasite infection too. Preventatives are highly effective when given at the proper dose year-round. The American Heartworm Society advises against seasonal treatment such as stopping preventatives during the winter months in northern states. Talk to your veterinarian about heartworm disease testing and preventatives.

How is heartworm disease treated?
If your dog tests positive for heartworm disease, there are treatments available. Success and safety of treatment depend on the duration of infection and the number of worms. Yearly heartworm testing is important in helping to catch the disease in the early stages. Treatment requires oral medications followed by hospitalization for a series of injections, then an extended period of inactivity. More severely affected dogs have an increased likelihood to experience complications following treatment. Treatment for heartworm disease is expensive and your dog could have lasting effects from the damage to the heart and lungs. Unfortunately, the medications used to kill heartworms in dogs are not safe for use in cats.

Yearly heartworm testing and monthly year-round preventatives are the most effective path to safeguard your pet's life. As with most things, when dealing with heartworm disease an ounce of prevention is worth a pound of cure!

About Dr. Kaitlin Fitch

A lifelong animal lover, Dr. Fitch decided on a career in veterinary medicine at the age of four when the local vet visited her preschool. After earning a degree in biology from the University of Massachusetts Amherst, her dream was realized in 2004 when she graduated from Tufts Cummings School of Veterinary Medicine. Following graduation, Dr. Fitch joined a clinic in Wrentham, MA where she practiced small animal medicine for the past 13 years.