Parasitic Worm Infestation from Insect Bite
A 74-year-old man from California experienced an alarming turn of events after being bitten by an insect. Instead of just a bothersome itch, he found himself dealing with a parasitic worm infestation in his eyelid.
Doctors from UCLA detailed this unusual case in a recent report, noting that the species of parasite involved had never been documented in the U.S. before. Thankfully, after the worm was discovered, it was safely removed, and the man made a full recovery without any complications.
In their report, the authors emphasized the importance of molecular and histological studies for identifying nematode infections. This was published in the July issue of *Emerging Infectious Diseases*.
An Unexpected Invader
As the report explained, the man was bitten by an unidentified insect on his lower left eyelid. Initially, he felt brief pain and noticed some swelling and fluid coming from the bite area. However, six weeks later, when he visited his dermatologist, a firm, non-painful nodule measuring eight millimeters was observed in the same location. Further, an ophthalmologist conducted an MRI, which revealed what appeared to be a cyst on his eyelid. Initially, doctors suspected it was a chalazion, a common benign lump caused by a blocked oil gland.
Chalazions usually resolve on their own in a few weeks, but five months later, the lump was still present. Consequently, the medical team opted for removal and biopsy. The surgery proceeded smoothly, and after testing, it was revealed that the nodule was actually a nematode, or roundworm.
The parasite bore resemblance to a group of nematodes known as *Dirofilaria*, and genetic analysis later confirmed it as *Dirofilaria repens*. This particular worm has a complex life cycle that involves mosquitoes and their natural hosts, like dogs and raccoons. Humans inadvertently become dead-end hosts, unable to allow the worms to grow and reproduce fully within our bodies.
In the Americas, infections typically stem from *D. immitis*, which causes heartworms in dogs, or *D. tenuis*, associated with raccoons. Conversely, *D. repens* is a common causative agent in parts of Europe, Asia, and Africa, indicating this is the first known case in the New World, according to the researchers.
How Did It Get Here?
Recent studies have identified *D. repens* in South American mammals, particularly the ring-tailed coati. However, a nationwide survey conducted in 2022 in the U.S. found no genetic evidence of the worm in domestic animals, raising questions about how it entered the country.
The man reported no recent travels, leading researchers to suspect he may have contracted the worm through a domestic host nearby. Additionally, the rising population of *Aedes* mosquitoes in California—known to transmit various diseases, including *Dirofilaria*—could be linked to this incident. The researchers noted that while the increase in *Aedes* mosquitoes may be a factor, the absence of concrete surveys for *D. repens* among wildlife in California limits definitive conclusions.
Human infections from *Dirofilaria* are generally rare, and cases involving *D. repens* in the eyelid tend to be localized and easily treated. In this instance, the man was symptom-free six months post-surgery. However, the emergence of this parasite in a new area is indeed concerning, and the scientists advocate for more follow-up research.
They concluded by stressing that the presence of *D. repens* in the United States calls for ongoing surveillance.
