Why Do We Recommend Annual Heartworm Testing?

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Heartworm is a disease that is spread by mosquitoes.  The adult worms live in the heart and as you can imagine, this makes the heart pump less effectively. In order for a dog to contract heartworm disease, it must be bitten by a mosquito that has previously bitten a heartworm infected dog. The juvenile heartworm (larva) goes through a developmental stage in the mosquito kidney. After this happens the next dog bitten can be infected with heartworm disease. It then takes 6 months for the  heartworm  larva that was injected into the dog by the infected mosquito to reach adulthood and take up residence in the dog’s heart. After 6 months the adult worms can release new juvenile heartworms into the dog’s blood stream to be picked up by mosquitos. This is an important bit of information as it explains why we do not need to heartworm test puppies less than 6 months of age. Another important point here is that heartworm disease is detected by a blood sample not as many people believe, from a stool sample. The blood test detects a specific juvenile or larval form of the worm. There are a number of different larval forms involved in this process but might complicate the explanation and hence I will refer to larval forms in general.

We are fortunate to have very effective heart worm preventatives. The majority of which function as a “morning after” type medicines. They kill the larval forms of heartworms preventing them from reaching adulthood and taking up residence in the dog’s  heart.  Most of the companies that produce these meds will stand behind their product and compensate the pet owner  completely for treatment costs if there is a break in the meds and if a dog that is on heartworm prevention contracts heartworm disease.  The treatment for heartworm disease is not without risk and the best approach is prevention. In certain areas north of us heartworm prevention is given monthly from May to November. In this area the climate is such that we need monthly prevention all year round. There will be no compensation if  evidence  is not consistent with regular monthly heartworm prevention and annual testing. This explains the reason for annual heartworm testing.

Author: Dr. Marcy Rose

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