Heartworm Disease


Wednesday, July 19, 2023 - 23:45

By Sophy Jesty, DVM, DACVIM (Cardiology)

Heartworm disease is a prevalent, and potentially devastating, disease in the Lowcountry. The disease is transmitted by mosquitoes, so the warm weather in this part of the country increases the likelihood of dogs being affected, even if they are predominantly indoors. Heartworm disease cannot be transmitted directly between dogs because part of the life cycle requires a mosquito, but heartworm positive dogs put other dogs in the community at risk because a mosquito can pick up the disease from the affected dog and transmit it to other dogs. People cannot get heartworm disease, even if bitten by an infected mosquito.

Heartworm disease can be diagnosed with a simple blood test available in every veterinary practice. If a dog is unexpectedly positive for heartworm disease, the result should be confirmed with other tests. Mild heartworm disease does not cause any symptoms, but more severe disease can cause trouble breathing, coughing (sometimes with blood), exercise intolerance, collapse, abdominal distention with fluid, or even collapse of multiple organ systems resulting in death. Heartworm positive dogs should be treated as per the guidelines from the American Heartworm Society. There is always risk in giving the drug to kill heartworms (melarsomine), but the risk of leaving the heartworms to live within the lungs is greater, and therefore the ‘slow kill’ protocol is not recommended. The vast majority of dogs treated with melarsomine have no adverse effects associated with treatment, but if the dog has severe disease, the risk of treatment causing adverse effects increases. Occasionally, heartworms ‘fall back’ from the blood vessels in the lungs to the right side of the heart; this is referred to as caval syndrome and is imminently life threatening. Symptoms include profound weakness, collapse, abdominal distention, and pigmented urine. Treatment at this point necessitates surgical removal of the heartworms from the heart chambers prior to treatment with melarsomine.

Cats are infected with heartworm disease much less commonly than dogs, although it is possible, especially in the southeast. Symptoms include coughing, decreased appetite, vomiting, and weight loss. Treatment with melarsomine isn’t recommended in cats; instead a heartworm positive cat would be treated with heartworm prevention and an anti-inflammatory steroid.