Are the heartworms winning??

Transcript from this week's episode of The Web-DVM:

Are the heartworms winning?

Greetings, pet lovers, this is Dr. Roger Welton, veterinarian and Veterinary News Network Reporter.

Heartworm disease has been known to veterinarians more than 120 years. Transmitted from any of more than 70 known species of mosquitoes, the disease attacks the pulmonary arteries and the dog’s heart. Heartworms are spread directly to the dog from the mosquito, with no dog-to-dog transmission.

For more than four decades, heartworm disease has been effectively prevented in dogs by using available products. But recent research indicates this might be changing. Information released at a 2010 veterinary conference detailed a genetic mutation in heartworms that appears to confer slight resistance to current preventives. Anecdotal reports in the last 4-5 years also point toward an increase in heartworm prevention product failures in the Mississippi delta region of the U.S.
Lack of efficacy (LOE) to heartworm preventives remains geographically limited, but research is ongoing. Historically, the LOE was attributed to poor owner compliance, Hurricane Katrina effects, increased heartworm numbers within this mosquito vector, and/or the increased sensitivity of heartworm testing.

Two prominent veterinary groups, the Companion Animal Parasite Council (CAPC) and American Heartworm Society (AHS) concluded recently that most credible reports of LOE are geographically limited at this time. The extent of this problem is unknown.
Lack of conclusive evidence could also be due to:

• Poor Owner Compliance.

o Is the pet given preventive medication consistently?
o Is the pet ingesting the medication and not vomiting up, splitting out meds?

• Imperfect Clinical Testing & Education

o Dogs with inconsistent heartworm testing tested more often.
o Delayed maturity of heartworms potentially indicates a “negative” antigen test, leading to false sense of security.
o Heartworm tests may have become more sensitive.

This same study group concludes: “The potential for lack of efficacy of traditional control products is not a reason to abandon their use”. Emphasis is placed on the importance of annual heartworm testing.

The veterinary industry does recognize the dire consequences if resistance is confirmed. The American Heartworm Society will continue to support and monitor research. If resistance is confirmed, changes to preventive and therapeutic strategies may be implemented in the future.

The following are key veterinarian recommendations:

• Proper use of current heartworm preventives remains effective for the vast majority of dogs.
• Prevention strategies should not be abandoned.
• In heartworm disease confirmed cases, stage-specific medical management should be implemented.

The following are dog owner key recommendations:

• Annual heartworm disease testing, more often if missed preventives or high risk.
• Follow label directions on dosage and frequency.
• Reduce exposure to mosquitoes.
• Get examined by veterinarian immediately if symptoms appear in your dog…i.e. persistent cough, exercise intolerance, body wasting.
• Upon heartworm diagnosis, follow veterinary recommended treatment.
Heartworm disease is a complex issue. Until more is known about the extent of the issue, pet owners should trust current heartworm products as the best choice for prevention.

Follow your veterinarian’s recommendations, give heartworm prevention monthly year-round and test annually to ensure that you are protecting your pets.

This is Dr. Roger Welton reporting, for The Web-DVM.

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Dr. Roger Welton is the President and chief veterinarian at Maybeck Animal Hospital in West Melbourne Florida, as well as CEO of the veterinary advice and health management website Web-DVM.net.