Pet owners are concerned current heartworm prevention medicines may no longer be an effective treatment due to the development of heartworm resistance. To date, research has not found a resistant strain of heartworms – although the American Heartworm Society and the Companion Animal Parasite Council agree:-

“There is evidence of genetic variation within some heartworm populations that may be associated with decreased susceptibility to macrocyclic lactones” (heartworm preventives).

The advice is very strongly that Pet owners should continue with current preventative heartworm treatment for dogs. See referenced article here on the Veterinary News Website. In addition, an annual heartworm test is recommended.

Both these eminent bodies agree that any lack of efficacy of heartworm preventives is obscured by lack of compliance.

Studies show that 50 percent of pet owners that provide their dogs with monthly dog heartworm medicine do not give the medicine as directed.

This may account for the high number of dogs that are infected with heartworms even though the dogs are given a monthly heartworm treatment.

Veterinarians and researchers have studied the life cycle of heartworms and feel strongly that the heartworm medicine cannot cause heartworm resistance.

It is believed that most infected dogs were infected because the medication was not administered properly however, please see the report in the video below for more information.

Monthly heartworm treatment kills the larvae in the blood stream. The medicine should be given every 30 days. If this protocol is not followed, it is possible for a dog to become infected. A current lawsuit against a heartworm treatment product has caused rising concerns among dog owners. However, heartworm resistance has not been proven. It is more likely that the dose of monthly treatment is insufficient in areas of the world where the mosquito population is increasing or the dog owners did not administer the dose properly.

It is true that more dogs are becoming infected with heartworms and many of these dogs were given a monthly heartworm preventative. In many cases, the dog owner did not follow the appropriate schedule or did not make sure the dog consumed the entire dose. In addition, most of these cases are in areas such as the Gulf Coast where the mosquito population has risen significantly over the past 10 years. If heartworm resistance is developing, it has not yet been discovered. More research is needed to determine if heartworm resistance is truly the cause of rising heartworm infections.

This VNN video has useful information about heartworm resistance

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It is important for dog owners to make sure the monthly preventative medicine is given every 30 days. In addition, it is crucial for dog owners to make sure their dog consumes the entire dose. Currently, the heartworm preventative medicine failure rate is less than one in a million. While you may have concerns about heartworm resistance, it is important to continue to treat your dog with a monthly heartworm prevention plan. Research will continue to determine if heartworm resistance has developed. Protect your pet with annual testing and continue with heartworm treatment.