Dirofilariais is caused by filarial nematodes (roundworms) of the genus Diroflaria. The three species most commonly reported to cause disease in humans are D. immitis , D. repens, and D. tenuis. Dogs and wild canids are the main natural hosts for D. immitis and D. repens and raccoons for D. tenuis. Humans are accidental hosts and the worms do not grow to maturity in humans. D. immitis causes heartworm disease in dogs. In humans infected with D. immitis, the most common clinical finding is lung granulomas, often asymptomatic, which appear as coin lesions on x-rays. Among persons infected with D. repens and D. tenuis, the most common findings have been nodules under the skin and under the conjunctiva of the eye.