• Heartworms and fleas are parasites that can cause serious problems. Fortunately, these parasites can be prevented by using safe, effective, and easy-to-administer medications.
  • Heartworm disease damages the heart, lungs, and related blood vessels and can be fatal. This disease is transmitted through the bite of an infected mosquito.
  • Heartworm disease in dogs is treatable, but in some cases, treatment can be costly and complicated. There are no approved products for heartworm treatment in cats.
  • Fleas are widespread, blood-drinking parasites that can transmit tapeworms and cause flea allergy dermatitis.
  • Prevention of heartworms and fleas is the best option for your pet.

Why Worry About Heartworms?

Heartworm disease is serious and potentially fatal. It affects dogs, cats, and up to 30 other species of mammals. Heartworm disease has been reported in all 50 states. It is caused by parasitic worms (heartworms) living in the major vessels of the lungs and, occasionally, in the heart. Heartworms are transmitted (as microscopic larvae) through the bite of an infected mosquito. The scientific name for the heartworm parasite is Dirofilaria immitis.

Heartworms can cause a variety of medical problems affecting the lungs, heart, liver, and kidneys. Any of these problems, alone or in combination, can lead to death. While treatment is available for dogs, it can sometimes be costly and complicated. In cats, heartworms can cause a respiratory disorder that mimics feline asthma. However, there is no approved medical treatment for heartworm disease in cats.

Although heartworm disease is virtually 100% preventable, many pets are still diagnosed with it each year. The American Heartworm Society (AHS) estimates that 1 million dogs in the United States are infected with the disease and that its incidence may be rising. Cats are susceptible to heartworms, too, and even indoor cats are at risk. Studies have shown that more than 25% of heartworm-infected cats live indoors.

Why Worry About Fleas?

The flea that most commonly affects pets is called the cat flea. Its scientific name is Ctenocephalides felis. The dog flea (Ctenocephalides canis) is much less common but can infest pets as well. Fleas not only make pets and people miserable but can cause serious health problems. In mild cases, pets may only be troubled by persistent itching and scratching. In some unfortunate animals, however, fleas can also cause an extreme allergic reaction resulting in intense itching. This causes the pet to scratch excessively, leading to skin damage, hair loss, scabs, and skin infection. This condition, called flea allergy dermatitis, can become severe enough to require extensive treatment. The bite of just a single flea can cause this kind of reaction in some highly allergic pets.

Fleas can also transmit tapeworms to pets and people. In some cases, they can play a role in transmitting an unpleasant disease called cat-scratch fever, between cats and humans. And in severe infestations, particularly in old, ill, or young animals (puppies or kittens), feeding fleas can remove so much blood from a pet that they can cause a debilitating and even life-threatening anemia.

Fleas can be found almost everywhere at any time of year. Depending on where you live, they may seem less prevalent during cooler months, but they can still survive through the winter on pets and in homes. They can be brought into your yard or even your home by wildlife, such as raccoons, opossums, and small rodents.

Treating Heartworm Disease

In dogs, if heartworm disease is detected early enough, it can be treated before permanent damage is done to the heart, lungs, and blood vessels. However, if the infection has been present for a long time or consists of a large number of worms, the risk of complications can increase. In these cases, treatment can be more expensive and complicated, and dogs may need many months to recover from the infection. Hospitalization may be required.

For cats, there is no approved medical treatment for heartworm disease. Your veterinarian can discuss with you how to monitor your cat and manage the signs of disease. Antibiotics, steroids, and other medications are sometimes recommended. For cats with severe breathing problems or other complications, hospitalization may be needed. In some cases, surgical removal of adult worms may be attempted. However, this surgery is costly and has some risks.

Treating Fleas

Once a flea infestation is established, it can be very difficult to eradicate due to the complex life cycle of these pests. Fleas have four life stages: eggs, larvae, pupae, and adults. Several of these stages can live in the environment (off of your pet). For every flea you see on your pet, there are probably hundreds more lurking in their egg, larval, or pupal forms in your pet’s living environment, just waiting for the right conditions to hatch or develop into blood-sucking adults. As a result, treatment for their removal is usually multi-pronged and may take several months of consistent effort.

First, you must treat every pet in your home, whether or not you see fleas on them. Some flea treatment products target adult fleas, whereas others may also kill the immature stages (eggs, larvae, or pupae). Ask your veterinarian which option is recommended for your pets.

Other management measures may include frequent vacuuming of carpets and laundering of pet bedding to remove fleas, eggs, larvae, or pupae that may be hiding in those places. In some cases, your veterinarian may also recommend treating the home with an area spray or fogger. If your pet is allowed outside, your veterinarian may want to discuss treating “flea-friendly” outdoor areas (such as crawl spaces, shrubs, and moist/shaded areas) with pesticides.


Fleas and heartworms can be easily prevented by using safe, effective, and easy- to-administer monthly medications. Some of these products are given orally, whereas others are applied topically to the pet’s skin (these are called spot-on medications). There is also an injectable heartworm preventive for dogs that can be administered every 6 months by your veterinarian.

Some heartworm and flea preventive products have the added benefit of also controlling other internal parasites of concern, such as roundworms and hookworms (in dogs and cats) and whipworms (in dogs). Some products also target other external parasites, such as ticks and mites.

In some cases, the best protection for your pet may not be the use of a single product, but rather the simultaneous administration of more than one product to effectively control parasites. Your veterinary team can help you decide which strategy may be best for your pet.

Preventing heartworms and fleas before they can become a problem is the safest, smartest, and most effective way to combat these parasites and keep your beloved canine and feline friends healthy! Ask your veterinarian which product(s) he or she recommends for your pet’s situation.

Caution: Some parasite control products cannot be used on cats. Consult your veterinarian regarding which specific products can be used for cats to safely prevent fleas and heartworms.