What is heartworm disease?
Heartworm disease is a serious and potentially fatal disease in pets in the United States and many other parts of the world. It is caused by foot-long worms (heartworms) that live in the heart, lungs and associated blood vessels of affected pets, causing severe lung disease, heart failure and damage to other organs in the body. Heartworm disease affects dogs, cats and ferrets, but heartworms also live in other mammal species, including wolves, coyotes and foxes.
The mosquito plays an essential role in the heartworm life cycle. Adult female heartworms living in an infected animal produce microscopic baby worms called microfilaria that circulate in the bloodstream. When a mosquito bites and takes a blood meal from an infected animal, it picks up these baby worms, which develop into infective larvae. Then, when the infected mosquito bites another animal, the infective larvae are transmitted through the bite. Once inside a new host, it takes approximately 6 months for the larvae to mature into adult heartworms. Once mature, heartworms can live for 5 to 7 years in dogs and up to 2 or 3 years in cats.
Do I have to give heartworm prevention to my indoor pet? What about winter?
It is impossible to predict which pets will be exposed to heartworms as risk factors are unpredictable. Multiple variables, from climate variations to the presence of wildlife carriers, cause rates of infections to vary dramatically from year to year. And because infected mosquitoes can come inside, both indoor and outdoor pets are at risk. Northern states can rely on consistently cold temperatures to keep insects in the dormant states during the winter, but those random warm days we experience in the south mean mosquitoes are a year round threat. This is why we recommend monthly heartworm, flea and tick prevention 12 months a year.
My cat needs heartworm prevention too?
Heartworm disease in cats is very different from heartworm disease in dogs. Cats with adult heartworms typically have just 1-3 worms, which makes testing unreliable. Those 1-3 worms can cause a significant amount of damage though and cats can actually experience sudden death when a worm enters the pulmonary arteries and blocks the flow of blood to the lungs. There is also no medication that can be used to treat heartworms infections in cats and once infected, those worms will live for 2-3 years. Additionally, many people are surprised to learn that 1/3 of infected cats are strictly indoor pets, so every cat should be on prevention year round.
Why does my dog need to be heartworm tested every year?
Annual testing is necessary, even when dogs are on heartworm prevention year-round, to ensure that the prevention program is working. Heartworm medications are highly effective, but dogs can still become infected. If you miss just one dose of a monthly medication—or give it late—it can leave your dog unprotected. Even if you give the medication as recommended, your dog may spit out or vomit a heartworm pill—or rub off a topical medication. Heartworm preventives are highly effective, but not 100 percent effective. If you don’t get your dog tested, you won’t know your dog needs treatment. Additionally, heartworm prevention manufacturers will only guarantee their product if it is purchased from a veterinarian and your pet is tested annually. If your pet gets infected and meets both of these conditions, the company will pay for any treatment necessary.