Protect Your Pet From Heartworm

Originally published in WLFS Feed for Thought Newsletter - May, 2008.
Written by Dr. Dan Kelly - Stonecliff Animal Clinic

Heartworm season is upon us. Warmer weather has found its way into the Upper Valley and as the thermometer climbs, our daydreams about long, lazy days sipping lemonade out in the garden are finally becoming a reality. But the warmth brings out the bugs and the bugs bring on the risk of heartworm. During this season, please remember that mosquito bites do more than cause irritation; they have the potential to sicken or even kill your furry best friend.

As the name implies, heartworms are a parasite that take up residence in the heart of an infected dog or cat. But how, you may ask, does a pet acquire such a disgusting disease? Think back to that day sipping lemonade in the garden, with Fluffy at your side. You may not have realized that at that moment Fluffy was actually a sitting-duck for heartworm. Transmission takes place when, for example, the mosquito bites your neighbor’s pet, who happens to be infected, and then comes over and bites your pet. The mosquito, while feeding on her meal of blood, also transmits infected larvae into Fluffy’s bloodstream. These “baby” heartworms then spend about four months traveling around the body, growing through several larval stages and finally reach adulthood in the heart. At this stage, what was once a microscopic larvae can now reach up to 11 inches long as an adult. The worms will now clog the heart and connected vessels and, if left untreated, will lead to heart failure and death.

Both cats and dogs are vulnerable to heartworm disease, although it tends to be more common in canines. This is due to the fact that cats are not natural hosts for heartworm, which means that a cat’s body does not provide as ideal an environment for the development of larvae. The cat’s immune system is also very sensitive to the invading worms and migrating larvae will tend to get lost in the cat’s body, usually ending up in the lungs where they are destroyed by the immune system. This can cause problems for felines because the residue can accumulate in the lungs causing inflammation and may sometimes result in a fatal allergic-type reaction. These respiratory issues are often diagnosed as cat asthma in heartworm-positive cats.

So how do we know if a pet is infected? The process, which should be administered by a Veterinarian, is relatively simple and begins by drawing a small blood sample from the leg. For dogs, a test is run on the sample that will detect the presence of adult heartworms. However, because cats will generally have very few heartworms that survive in their bloodstream, the quantity may not be enough to trigger a positive result on this particular test so a different test is administered for cats that analyzes different components in the blood. The test will give results indicating that a cat is either infected, has immature worms in its body, or has a past infection. To clarify if the cat has a current infection, further signs of the disease are looked at through radiograph or ultrasound.

Prevention is the key for stopping the spread of heartworm. We recommend that all dogs in the Upper Valley be on a six-month preventative heartworm medication. This means that heartworm medication should be administered once a month for the entire season (May through October.) If pets are brought to warmer climates during the winter months, a year-round treatment schedule is recommended.

Owners who faithfully treat their pets for heartworm generally do not need to be tested every spring. For regular patients, heartworm treatment can simply be picked up at the clinic during your annual checkup. For patients who have had any lapse in the administration of preventative medication are required to be tested before resuming treatment.

-Dr. Dan Kelly