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Although you may think that your pet is safe from heartworms, heartworm-infected animals and the mosquitoes that transmit the disease have been positively identified throughout this region of the state.  Several cases have even been diagnosed at Rustburg Veterinary Clinic, each time in pets who had not been given preventive medicine.

Heartworm has been diagnosed in dogs in all parts of the world and in all 50 states, and is actually very common. The disease has virtually a 100% prevalence rate in unprotected dogs living in highly endemic areas, which includes the majority of the southeastern and midwestern USA. Because of this vast reservoir of dogs, coyotes, and other mammals infected with heartworms, future eradication of the disease in Virginia is highly improbable, and unprotected animals are at very high risk.

Heartworm, caused by the organism Dirofilaria immitis, is transmitted by mosquitoes. The mosquito injects a microscopic larvae, called a microfilaria (small heartworm), while feeding. These larvae penetrate various tissues and travel throughout the body as they grow through two life stages, until the juvenile worms penetrate veins, which carry them to the heart and lungs. Here, the juvenile grows into an adult worm six to eighteen inches long inside the pulmonary arteries and heart of the affected dog. This process takes four months for the worms to reach sexual maturity, and new microfilariae are ready to pass to a feeding mosquito 7-9 months post infection.

As the worm burden increases, blood flow to the lungs is obstructed, and heart valves will be prevented from closing fully. The worms can cause mild outward symptoms (such as coughing) at first, but with time, more severe symptoms such as congestive heart failure, weight loss, fluid build up in the abdomen, fainting spells, anemia, collapse, and death usually occur.

This video, taken here at Rustburg Veterinary Clinic, shows heartworm larvae in blood.

We do have several excellent medications which can prevent heartworm if given as directed. There are oral medications, which need to be given monthly and which also help protect against some intestinal parasites, and there is one topical medication which is also applied monthly and protects against fleas as well as heartworms. Dr. Hubbard can help you determine the best preventive for your pet based on a number of factors. Prevention of diseases is better for the health of your pets, more effective, safer, and more economical, and heartworm disease is no exception. If a dog has heartworms and it is given a dose of preventive, there can be a reaction that is detrimental to the dog, or even deadly. It is possible to treat canine heartworms, and a veterinarian can determine the appropriate course of treatment; however, sometimes the treatment is also potentially harmful to the dog.

Because all dogs living in heartworm-endemic areas are at risk, prevention is a high priority. The peak months for heartworm transmission in Virginia are usually July and August; however, heartworms can be transmitted to dogs and cats nearly year-round, so it is important to continue to protect your pets throughout the year. We recommend that puppies be started on preventives as early as possible, between 6 and 8 weeks of age. Even if a dog has been given preventives, it is still important to have annual checkups for heartworms by doing a blood test. Our preferred test is the 4Dx+ test, which tests for 3 tick-borne diseases (Lyme disease, Ehrlichiosis, and Anaplasmosis) in addition to testing for heartworm infection.

Finally, a note about non-prescription heartworm prevention: all legal heartworm prevention requires authorization by a licensed veterinarian having a valid relationship with the pet and owner. Products that you may have found that do not require a prescription are illegal. They may be unsafe for your pet, and they may not even contain the medicine you believe they do and for which you are paying. These illegal products are often counterfeit, outdated, mislabeled, incorrectly formulated, or improperly made or stored. They may not contain the correct dosage of drug if they even have the correct drug at all, may contain contaminants, and may not work as well due to age or being stored in improper conditions. Manufacturers warranties are not valid for these illegal, possibly dangerous, or at the very least, ineffective products. The prescription medications dispensed by veterinarians have been tested and proven safe and effective to the satisfaction of the FDA, an expensive and demanding task taken on by the manufacturer of the medication. Even this year at RVC, we have identified counterfeit heartworm medication that was sold online to our clients and did not originate from legitimate manufacturers of heartworm preventive.

For our sources and for more information, we recommend the following resources:

American Heartworm Society

Companion Animal Parasite Council

American Veterinary Medical Association

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