A 74-year-old man in Southern California sought medical attention for a bump on his lower left eyelid that had persisted for five months. Initially suspected to be a common stye or cyst, the growth was surgically removed and analyzed. Researchers discovered the bump was caused by Dirofilaria repens, a type of nematode or roundworm, which had never before been recorded as infecting humans within the United States.
The man reported that the bump appeared after an insect bite, accompanied by pain and swelling that later subsided. Microscopic examination revealed the presence of the worm, which is typically found in the skin of dogs and cats and is transmitted to hosts through mosquito bites. While the parasite is endemic in Europe and has been found in South America in recent years, its detection in a U.S. patient who had not traveled abroad suggests a potential local transmission.
Prior infections with Dirofilaria worms in the U.S. have involved different species, such as Dirofilaria immitis (heartworm in dogs) and Dirofilaria tenuis (found in raccoons). The Centers for Disease Control and Prevention (CDC) noted that increasing mosquito populations in California might contribute to a higher risk of such infections.
Symptoms of Dirofilaria repens infection in humans can include localized swelling or inflammation. In more severe but rare cases, individuals might experience coughing up blood, chest pain, fever, and breathing difficulties. The infection can also affect the eye and potentially lead to vision loss if not treated.
Ophthalmologists advise that persistent bumps on the eyelid that do not resolve with conventional treatments should be evaluated by a medical professional. The U.S. case was successfully treated with surgery, and the patient recovered without any vision loss.
Experts recommend preventing mosquito bites as the primary method to avoid infection, suggesting measures like covering exposed skin. Individuals suspecting such an infection are urged to consult a healthcare provider for diagnosis and treatment.