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Dogs that do not take prevention medicine are susceptible to heartworm disease through contact with infected mosquitoes. Heartworm disease occurs in all 50 states and across the globe — but luckily, it’s preventable.

When an infected mosquito bites the dog, heartworm larvae are likely to transmit the disease to the pet, entering through the skin’s bite wound and into the bloodstream. As the worms grow and multiply, they generally migrate and live in the arteries of the lungs and heart. The FDA reports that some of these heartworms can grow up to a foot in length.

And while there are a variety of mostly-successful treatment options for dogs that become infected with heartworm disease, it is a complex and expensive course of action (not to mention the canine’s discomfort while suffering from heartworm disease).

The American Heartworm Society recommends that dog owners talk with their veterinarian about heartworm disease and the best methods for disease prevention. So recently I connected with Dr. Amara Estrada, Assistant Professor at the University of Florida College of Veterinary Medicine, to learn more about the different heartworm disease prevention options for dogs.

Dr. Estrada shared with me that “it is strongly recommended that all dogs be placed on chemoprophylaxis. There are two major classes of chemoprophylactic agents to prevent heartworm infestation — diethylcarbamazine and the avermectins. Diethylcarbamazine is rarely used anymore as avermectins provide better protection and ease of use.”

Currently, there are three types of avermectins in the United States that prevent heartworm in dogs and cats. These include: Ivermectin (Heartguard, Heartguard Plus), Milbemycin oxime (Interceptor) and Selamectin (Revolution).

Heartworm prevention medicines disrupt the development of the worms before they can enter the bloodstream and grow, multiply, and migrate to the arteries of the lungs and heart. Medicines are generally administered to dogs in the form of daily or monthly tablets/chewables, as a topical liquid, or via a six-month injectable. The American Heartworm Society deems all of these medicines as effective at preventing heartworm disease in canines — when administered according to guidelines — and states that “heartworm prevention is safe, easy and inexpensive.”

Dr. Estrada adds that “the goal of heartworm prophylaxis is to prevent infestation of individual animals. The duration of yearly prophylaxis depends on climate to determine larval transmission — the average daily temperature must be at least 14° C (57° F) for larvae to mature to the infestive stage before the mosquito dies. Prophylaxis may be required for as few as 3 months or as long as 12 months.”

Although heartworm disease is dangerous and potentially fatal in canines, there are no laws in the United States mandating that prevention medicines be used. Dog owners are solely responsible for consulting with a veterinarian about heartworm prevention options and to faithfully maintain a regular schedule of medicine administration.

In February, 2010, the American Heartworm Society released new canine heartworm guidelines — check out the full report here. The current recommendation is that all dogs receive year-round heartworm prevention, even in seasonal areas of the United States.

Want to learn more about heartworm disease in dogs? Visit the American Heartworm Society website for up-to-date information and read some tips for consumers from the FDA here.

Fascinated by animal diseases? Check out the Nat Geo WILD show Curse of the Tasmanian Devil to learn about how cancer is drastically reducing this species’ numbers.