Heartworms are deadly!

Ever wonder what a heartworm positive dogs heart can look like? 

This is why we are so adamant about heartworm prevention, especially in the spring and summer months when the mosquitos are out. A heart like this cannot function properly. Heartworms are deadly!

Heartworm disease is a serious disease that results in severe lung disease, heart failure, other organ damage, and death in pets, mainly dogs, cats, and ferrets. It is caused by a parasitic worm called Dirofilaria immitis.The worms are spread through the bite of a mosquito.  The dog is the definitive host, meaning that the worms mature into adults, mate, and produce offspring while living inside a dog.  The mosquito is the intermediate host, meaning that the worms live inside a mosquito for a short transition period in order to become infective (able to cause heartworm disease).  The worms are called “heartworms” because the adults live in the heart, lungs, and associated blood vessels of an infected animal.    

In the United States, heartworm disease is most common along the Atlantic and Gulf coasts from the Gulf of Mexico to New Jersey and along the Mississippi River and its major tributaries, but it has been reported in dogs in all 50 states. 

The Heartworm Life Cycle in Dogs

In an infected dog, adult female heartworms release their offspring, called microfilariae, into the dog’s bloodstream.  When a mosquito bites the infected dog, the mosquito becomes infected with the microfilariae.  Over the next 10 to 14 days and under the right environmental conditions, the microfilariae become infective larvae while living inside the mosquito.  Microfilariae must pass through a mosquito to become infective larvae.  When the infected mosquito bites another dog, the mosquito spreads the infective larvae to the dog through the bite wound.  In the newly infected dog, it takes about 6 to 7 months for the infective larvae to mature into adult heartworms.  The adult heartworms mate and the females release their offspring into the dog’s bloodstream, completing the life cycle. 

Heartworm disease is not contagious, meaning that a dog cannot catch the disease from being near an infected dog.  Heartworm disease is only spread through the bite of a mosquito.

Inside a dog, a heartworm lifespan is 5 to 7 years.  Adult heartworms look like strands of cooked spaghetti, with males reaching about 4 to 6 inches in length and females reaching about 10 to 12 inches in length.  The number of worms living inside an infected dog is called the worm burden.  The average worm burden in dogs is 15 worms, but that number can range from 1 to 250 worms. 

Can Cats Get Heartworm Disease?
Is Heartworm Disease Different in Cats?

Cats can also get heartworms after being bitten by an infected mosquito, although they are not as susceptible to infection as dogs.  A cat is not a natural host of heartworms because the worms do not thrive as well inside a cat’s body.  Both indoor and outdoor cats are at risk for heartworm disease.

Heartworm disease in cats is a bit different than in dogs.  Heartworms in cats do not live as long (average lifespan is only 2 to 4 years) or grow as long, and fewer of them mature into adults.  Worm burdens are lower in cats than dogs. Usually a cat has only one or two worms. However, due to its relatively small body size, a cat with only a few worms is still considered to be heavily infected.

In cats, it takes 7 to 8 months for infective larvae to mature into adult heartworms and produce microfilariae.  This is about one month longer than in dogs.  The presence of microfilariae in a cat’s bloodstream is uncommon.  Only 20 percent of cats with heartworm disease have microfilariae in the bloodstream, compared to 80 to 90 percent of dogs with heartworm disease.  Also, the presence of microfilariae in the bloodstream is inconsistent and short-lived in cats.   

It is harder to detect heartworm infections in cats than in dogs. Veterinarians generally use two types of blood tests in combination to check a cat for heartworms.  However, negative test results do not rule out heartworm infection, and positive test results may or may not mean that there is an active heartworm infection.  A veterinarian uses the results of both blood tests, along with the cat’s symptoms and the results of other tests such as x-rays and an ultrasound of the heart, to determine if a cat has heartworm disease.

Again, Prevention is the Best Treatment!

Several products are FDA-approved to prevent heartworms in cats.  There are both topical and oral products for cats, and all are given monthly and require a veterinarian’s prescription. Some heartworm preventives contain other ingredients that are effective against certain intestinal worms (such as roundworms and hookworms) and other parasites (such as fleas, ticks, and ear mites).

Again, year-round prevention is best!  Talk to your cat’s veterinarian to decide which preventive is best for your cats.