Heartworm Disease

Although heartworm infection is predominantly present in the southeastern United States, relocation of animals after natural disasters and through rescue efforts in recent years has driven a major influx of heartworm positive animals into areas such as Illinois. This has increased the risk of heartworm disease transmission in our local area and makes it even more important to understand how transmission occurs and what we can do as animal caretakers to prevent it.

Heartworm disease is caused by a footlong roundworm (Dirofilaria immitis) that, in its adult form, resides in the heart and lungs of infected animals. If multiple adults are present in a single animal, this parasite creates larva called microfilaria which travel through the bloodstream. Transmission of heartworm occurs when the microfilaria are taken up by a mosquito during a blood meal and then injected into an uninfected animal at a later bite. Heartworm evolved to complete this life cycle in canid hosts such as dogs, coyotes, foxes, and wolves. However, it can also develop atypically in cats, ferrets, and even sea lions!

The development of heartworm disease causes damage to the heart and lungs which can be extremely dangerous and sometimes even fatal. Medical and surgical treatments exist for heartworm positive dogs to kill and remove adult worms. These medical interventions require months of activity restrictions and administration of multiple drugs to kill the microfilaria, adults, and commensal bacteria (Wolbachia) which help the worms reproduce. Cats and ferrets are unlucky atypical hosts and cannot be cured of heartworm disease through medication. Therefore, these pets have more fatal complications associated with the disease.

For pets susceptible to heartworm infection, prevention and early detection should absolutely be key factors in their healthcare plans. Early detection via annual blood tests reduces the long-term ill effects these worms can inflict on the heart and lungs. Prevention negates complications altogether. Numerous heartworm preventatives are currently on the market ranging from monthly oral and topical drugs to longer lasting injections such as ProHeart-6. These medications typically have added benefits including treatment of some common gastrointestinal parasites. 

Heartworm preventatives specifically target larva present in the tissues under the skin before they reach the blood vessels. Larva spend approximately 2 months after infection in this stage of their life cycle. For this reason, it is extremely important to use preventatives year-round rather than assuming the pet is safe during the winter solely because adult mosquitos are no longer present.

It is also important to recall that oral and topical prevention drugs kill larva which developed the month prior to administration rather than preventing infection in the month ahead. ProHeart-6 ensures no gaps in coverage occur by being constantly present in the body for 6 months after injection. When used appropriately year-round, heartworm preventatives are highly effective at protecting dogs, cats, and ferrets from experiencing this serious disease.

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