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Dog Owners Encouraged To Be Aware Of Heartworm Risk As Temperatures Rise

Rising mosquito activity heading into the summer months poses an increased risk of transmitting heartworm disease to dogs, which can lead to damage of the heart, lungs and arteries if left untreated.

Cathy Campbell, DVM, veterinary diagnostician at the Texas A&M Veterinary Medical Diagnostic Laboratory, TVMDL, in Bryan-College Station, explains the heartworm life cycle, the best time for testing, and tips for prevention.

What are heartworms and how are they transmitted to dogs?

Heartworm disease is caused by the parasitic worm Dirofilaria immitis and is transmitted to animals through mosquitoes, according to the American Heartworm Society. Mature heartworms can live within dogs for up to seven years.

"When a mosquito happens to bite an animal infected with heartworms, it ingests microfilariae, or baby heartworms, through a blood meal," Campbell said.

Those microfilariae morph into larvae inside the mosquito in 10-14 days. That infected mosquito tends to fly around and bite a dog, transmitting the larvae to a new host. Once transmitted, the larvae enter the dog's bloodstream and migrate to the heart.

"Larvae set up housekeeping in the heart and grow into sexual maturity in six to seven months," Campbell said. "Mature worms produce microfilariae, which are released into the bloodstream where they await another mosquito to come and bite the dog, take up a blood sample and continue the cycle."

It takes six to seven months in the heartworm's life cycle before they can be detected on a test. Therefore, most veterinarians recommend testing dogs for heartworms around 6 to 7 months of age.

Testing to detect heartworms in dogs

TVMDL offers two different approaches to testing.

The first approach is to detect the baby heartworms produced by adult heartworms in the heart. TVMDL's clinical pathology section can detect microfilariae using either a filter method or through a modified Knott's test.

However, not all heartworm infections produce baby heartworms, so it is best to include an "occult" heartworm test using an enzyme-linked immunosorbent assay, ELISA — the second testing approach.

Technicians at TVMDL use the ELISA test to detect antigens associated with pregnant female heartworms. A positive result indicates adult female heartworms are present. This is the primary testing method to detect heartworms.

TVMDL's role in testing for heartworm disease

Most private veterinary clinics can perform heartworm antigen/ELISA testing in-house, Campbell said. TVMDL primarily conducts confirmatory heartworm testing with a different antigen test after these clinics have gotten an initial positive result.

Confirmatory testing is performed for several reasons. The first is to confirm a dog truly is positive for heartworms prior to undergoing treatment, because the treatment drug used for heartworms can have significant side effects and should not be used unless adult heartworms are present.

The second reason is to document heartworm prevention drug failure. Several manufacturers guarantee coverage of treatment for a dog that has been on their product but developed heartworms despite well-documented testing and dispensing of medication by a licensed veterinarian. There is evidence of a preventative-resistant heartworm variant, primarily in the Mississippi delta region of the U.S.

Lastly, sometimes test results can be unclear. TVMDL can offer a differing testing option to help support or confirm findings.

Although TVMDL serves a confirmatory role for most antigen heartworm tests, the agency typically conducts initial testing for the heartworm antibody test in felines. Due to the infrequency with which this test is needed in private practice on cats, many veterinary clinics do not perform this test in-house and defer testing to TVMDL.

Prevention recommendations

TVMDL encourages veterinarians to educate their clients on the benefits of giving year-round heartworm preventatives to both their canine and feline patients and supports annual testing of canines.

"Texas' mild climate lends toward year-round mosquito activity," Campbell said. "Missing a dose of heartworm preventative, or even administering a dose late, may allow a window of opportunity for mosquitoes to infect pets."

For additional information on heartworm disease, visit the American Heartworm Society. For more information on testing, visit TVMDL's testing services or call the TVMDL laboratory nearest to you.

Jett The Vet On How To Prevent Heartworm

When it comes to problems for your pup, spring brings more than muddy paws. It's also time to start thinking about heartworm prevention.

Jett Eder is a Veterinarian with Best Care Animal Hospital and Jaxson is his four-legged BFF,

They joined us to tell us everything we need to know to get our pups prepped for spring.

Jett Eder and Ashley Thompson on the KELOLAND Living set

Animal Chronicles: Heartworm Disease In Our Pets

Heartworms are exactly that: long worms (up to 14 inches, in fact) that, in adulthood, live in the heart and pulmonary arteries of an infected dog. These are very different than other types of parasitic worms, which typically live in the gastrointestinal tract.

Dogs acquire this infection through mosquito bites. A mosquito bites a heartworm infected dog and ingests tiny heartworm larvae along with their blood meal. That same mosquito then bites another dog, and the heartworm larvae then travel from the mosquito into the healthy dog. After the larvae are in the bloodstream they continue to develop over months into large adult worms and they reach and remain in the heart and lungs. Those adult worms then breed and create new larvae, which float around the bloodstream, waiting to either develop into more adult worms or get picked up by a mosquito to infect another dog.

Heartworm disease can be very dangerous and can create a variety of symptoms, including coughing, shortness of breath, panting, fluid accumulation in the chest or abdomen, fainting or even sudden death. Unfortunately, often by the time the dog is exhibiting clinical symptoms, heartworm disease is fairly advanced.

If a dog does get heartworm disease, treatment can be complicated and carry its own risks. Treatment is quite expensive. It typically requires multiple painful injections and it often makes the dog not feel well for a few days. Since the goal of treatment is to kill the worms, it does put dogs at risk of blood clots from the broken-up bits of worm. To try to prevent this risk, dogs need to be activity restricted during the treatment period, which can last up to three months.

Luckily, preventing heartworm is safe and effective. Heartworm prevention is typically a chewable tablet or topical medication you give your dog once a month (APF veterinarians recommend giving year-round). The medication kills any heartworm larvae that have entered your dog's bloodstream from a mosquito bite, which prevents them from developing into adult worms and infecting your dog. Therefore, heartworm prevention tablets actually work on the month prior to administration by killing any larvae that may have gotten into your dog, rather than working in the subsequent month to prevent new larvae. Most heartworm prevention also contains medications to treat other intestinal parasites, and some have medications to treat and prevent fleas, ticks and sometimes even help repel mosquitos. A blood test to check for presence of heartworms is typically required before heartworm prevention can be prescribed, as starting prevention in a dog that is known to be infected with heartworms can be dangerous.

Cats can get heartworm disease as well though it is much less common and they tend to get a much lower burden of worms compared to dogs. Discuss the use of heartworm prevention for outdoor cats with your veterinarian.

The incidence of heartworm disease in the Northeast has increased in recent years. The transport of infected dogs from higher incidence areas (primarily Southern or Mississippi Valley states) to the region; climate change leading to a longer mosquito season; and the lack of consistent year-round administration of heartworm prevention all contribute to the rise of this disease.

Heartworm disease is a dangerous disease that can be fatal, but prevention is easy, safe and effective. So remember to ask your vet about their recommendations for which product to choose to keep your pets safe.

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