The Heartache of Heartworm Disease

Lucky, that is how I feel every time I go to work. As a veterinarian, each day poses new challenges, most bring joy and satisfaction but a few create sadness and a great sense of frustration. Heartworm disease is one of the main causes that can bring the latter to my day. There is sadness in having to tell a client that their beloved pet has a potentially life threatening disease and frustration in that this disease could easily have been prevented. If you love a dog, cat or ferret, do not let yourself be faced with the heartache of heartworm disease.

Heartworms (Dirofilaria immitis) are parasitic worms that live in the arteries of the lungs and occasionally the right side of the heart. Dogs and wild canids (e.g. coyotes, foxes and wolves) are the normal host but domestic cats, wild felids (e.g. bobcats and cougars) and ferrets can be infected as well. The life cycle of this parasite begins when an adult female heartworm release their young, called microfilaria, into an animal’s bloodstream. The microfilaria cannot mature into adult heartworms without first passing through a mosquito. Mosquitoes become infected while taking a blood meal from an infected animal. While in the mosquito the microfilaria mature to an infective larval stage. Then, when this infected mosquito bites another dog, cat or other susceptible animal, the infective larvae enter through the bite wound. During the next 6 months the infective larvae will mature into adult worms and migrate to the pulmonary arteries. Adult heartworms can grow 10 to 12 inches in length and can live for up to 7 years!

The pulmonary arteries are the blood vessels that carry the blood from the right side of the heart to the lungs to be oxygenated. It is here that the adult heartworms do their damage. They cause inflammation and irritation to the arteries and surrounding lung tissue, thickening the walls of the arteries and slowing the passage of blood. The speed of these damaging changes is dependent upon the number of heartworms present. Recently infected dogs and cats may exhibit no signs of disease. But over time as the damage to the pulmonary arteries worsen and as new heartworms accumulate, clinical signs become apparent. In dogs these signs include a mild persistent cough, reluctance to move and exercise, reduced appetite, weight loss, congestive heart failure and death. In cats, the clinical signs include vomiting, gagging, difficulty breathing, lethargy, weight loss and at times sudden unexpected death.

In dogs, usually all but the most advanced cases of heartworm disease can be successfully treated. But the treatment can be expensive and can pose risks for the patient as well. Your veterinarian can explain in detail these treatments. There are no approved treatments for heartworm disease in cats available in the United States. But cats have proven more resistant hosts to heartworm than dogs. Their immune system can often kill the parasite, but unfortunately for many cats, their system reacts severely to the dead worms causing a shock reaction, a life-threatening situation.

Hopefully it has become readily apparent that the prevention of heartworm disease is the primary goal. There are numerous excellent products available for dogs, cats and ferrets that are safe, easy and inexpensive. All of the products are extremely effective and when administered properly and on a timely schedule, heartworm infection can be completely prevented. These medications interrupt heartworm development before the larvae reach the lungs and cause disease. Heartworm preventatives generally require monthly administration, killing any larvae that your pet has acquired in the preceding 30 days. In cooler climates there is often a heartworm season, coinciding with the life and death of the mosquito population. Here in the greater Savannah area where we are blessed with a temperate climate, mosquitoes can be active all year long. Thus, our pets must receive heartworm prevention every month of the year!

Puppies should be started on monthly heartworm prevention no later than 8 weeks of age and should be tested annually. Many people fail to see the purpose of testing their dog annually. They feel that if they are giving the preventative monthly, why bother? The preventative is only effective when given timely! If it is given late or skipped for even a month there is potential for infection. Treatment for heartworms is much safer and more effective before clinical signs of disease develop. If you have your dogs tested only every few years, there will be time for damage to be done if they become infected. The small expense of a yearly test pales in comparison to the potential damage to your dog’s health.

Kittens, even indoor only cats (mosquitoes come inside too!), should be started on monthly heartworm prevention by 8 weeks of age as well. Testing for heartworms in cats is not as clear cut as in dogs, so please talk to your veterinarian for their recommendations on heartworm testing for your cat.

None of us in the veterinary profession want to be the one to tell you that your pet has heartworms, save us, yourself and your pet the heartache, talk to one of us today!

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