Dirofilariasis in humans is caused by Dirofilaria roundworms. The main natural hosts for the three Dirofilaria species that most frequently cause disease in humans are dogs and wild canids (such as wolves and foxes) and raccoons. Humans are infected with Dirofilaria larvae through mosquito bites. Infection can result in nodules under the skin or conjunctiva and lung granulomas (small nodules formed by an inflammatory reaction) that appear as coin lesions (small, round abnormalities) on x-rays, leading to diagnostic procedures to exclude more serious diseases.  (Credit: CDC)

For more on heartworm in humans, see the CDC page here.

For more on heartworm in dogs, see "Heartworm in Dogs" from the American Heartworm Society.