Protecting Your Pet from Mosquitoes: Heartworm, West Nile, and Prevention
Why Mosquitoes Are More Than a Nuisance for Pets
For dogs and cats, mosquito bites are more than an itch. Mosquitoes are the vector for heartworm disease (Dirofilaria immitis), a parasite that can cause serious, life-threatening illness in dogs and increasingly in cats. Mosquitoes can also transmit West Nile virus to horses, birds, and other animals, though cats and dogs appear relatively resistant to clinical West Nile disease. Understanding what mosquitoes transmit and how to prevent bites is important year-round in southern states and during warm months everywhere in North America.
Heartworm: The Big Risk for Dogs
When an infected mosquito bites a dog, it deposits heartworm larvae into the bite wound. Over approximately 6 months, these larvae migrate through the body's tissues and develop into adult worms that live in the pulmonary arteries and heart. A heavily infected dog can carry hundreds of worms. In the early stages, heartworm disease may have no visible symptoms. As disease progresses: reduced exercise tolerance, persistent cough, difficulty breathing, weight loss, and eventual heart failure. Prevention with monthly heartworm preventive (ivermectin or milbemycin-based products) is safe, inexpensive, and highly effective. Annual heartworm testing is recommended because no preventive is 100% effective and testing identifies infections before they progress.
Heartworm in Cats
Cats are not natural heartworm hosts, and larvae often don't survive to adulthood. However, even immature heartworms in cats can cause a serious inflammatory lung condition — heartworm associated respiratory disease (HARD) — that resembles feline asthma and can cause sudden death. There is no safe treatment for heartworm in cats; prevention is the only effective strategy. Monthly preventives like Revolution (selamectin) protect against heartworm in cats along with other parasites.
Pet-Safe Mosquito Control
DEET-based repellents are toxic to both dogs and cats — do not apply human mosquito repellents to pets. Pet-specific repellents using natural ingredients (citronella, lemon eucalyptus, geraniol) are available and provide some protection. Eliminating standing water from the yard reduces mosquito breeding. Time outdoor activity during low-mosquito periods (mid-morning, midday rather than dawn and dusk). Screen-in outdoor areas to provide protected outdoor time. The most important mosquito protection for pets remains year-round heartworm prevention prescribed by a veterinarian.