THE DANGERS OF HEARTWORM DISEASE

Of the many parasites that dogs and cats are prone to, heartworm disease is one of the deadliest.  Unlike the majority of parasites that are obtained through fecal-oral transmission, heartworm disease is transmitted through the bite of the mosquito.  While the risk of infection varies from state to state and even from community to community, the threat still remains to unprotected pets in every state, even pets that spend the majority or all of the time indoors (mosquitoes can get into the house).

Heartworm disease develops when a mosquito carrying microscopic larvae (“baby parasites”) bites a dog or cat.  These larvae make their way into the blood stream eventually ending up in the heart and the lungs.  As the larvae live in the blood, they sexually mature into adult heartworms over a 6-7 month period, growing up to 10-12 inches in length!  Adult female heartworms then release microfilariae (their young) into the blood stream.  When mosquitoes continue to bite the infected animal, they ingest the microfilariae along with blood allowing the disease to be transmitted to other cats and dogs.  Heartworms can live in an animal for 5-7 years and if that animal remains unprotected, the number of heartworms can become enormous (up to a hundred in dogs).

Heartworm disease may not be obvious at first, especially with dogs, because some dogs can be infected for many years before symptoms develop.  Symptoms you may notice include: mild persistent cough or trouble breathing, exercise intolerance, lethargy, decreased appetite, weight loss, and sudden death, especially cats, as this may be the only symptom noted.  The disease can progress to heart failure or sudden cardiovascular collapse due to obstruction of blood flow through the heart and lungs secondary to heartworms clogging up vessels, ultimately leading to death.

A simple blood test can detect this disease and is recommended once yearly in dogs or more often if the pet lives in or travels to a high risk area.  Cats are not routinely tested unless symptoms are present, because they often have a much smaller heartworm burden making the test unreliable.  The test cannot consistently detect the infection if the heartworms are not at least 6 months old (why we don’t test puppies).

Fortunately you can prevent this disease by keeping your dogs and cats on heartworm prevention once monthly.  There are chewable products that must be given once monthly which also de-worm against certain intestinal parasites, as well at topical products applied to the skin once monthly which protect against fleas and also against certain intestinal parasites.  It is always recommended to test your dog before initiating heartworm prevention because some preventatives can cause life-threatening reactions if given to a heartworm positive dog.  Your veterinarian can help you decide which product is best for your pet.

Heartworm prevention works by killing the baby parasites but if a heartworm test is positive, that means there are already adult heartworms present, warranting a separate treatment.  Treatment is almost always recommended unless medical reasons identify a dog as a poor candidate.  Without treatment, the disease will worsen and the risk of death is always present.  Treatment in itself can lead to serious health concerns as the dead parasites can cause further damage to the lungs and arteries.  Your vet will typically recommend further bloodwork, +/- urine test, and +/- radiographs before beginning treatment.  Unfortunately there is no treatment for cats at this time.

Heartworm preventatives are relatively inexpensive, highly effective, and safe if used properly.  The best way to protect your pet against this disease is to institute a monthly year-round prevention program.  Further information about heartworm disease can be obtained through the American Heartworm Society website at www.heartwormsociety.org

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