The case — and shocking images — were published Thursday in a report titled “Migrating Dirofilaria repens” in the New England Journal of Medicine, detailing a case in which a woman from Russia became host to a parasite through a mosquito bite. The report states the woman, who was not named, started showing symptoms after traveling to a rural area not far from Moscow, where she “recalled being frequently bitten by mosquitoes.”
She experienced only occasional itching and burning as the worm slithered under her skin.
Dirofilaria repens is a long parasitic roundworm that is spread by mosquitoes, according to the Centers for Disease Control and Prevention.
Dirofilaria are usually found in dogs or other carnivores, according to the CDC, but have been known to infest humans, too, especially in Europe and with certain species — D. repens, D. tenuis and D. immitis (better known as heartworm in dogs).
How? Thomas Nolan, director of the clinical parasitology laboratory at the University of Pennsylvania School of Veterinary Medicine, said mosquitoes ingest the microfilariae (the parasite's undeveloped embryos), which then travel to the insect's gut and mature into the first-, second- and third-stage larvae. The larvae then make their way into the mosquito's mouth parts and, Nolan said, when the mosquito bites an animal — or a human — they crawl quickly into the bite site.
Once in their new host, he said, the larvae mature into adult worms.
That is where things can get weird.
According to guidelines from the European Society of Dirofilariosis and Angiostrongylosis (ESDA), Dirofilaria repens typically appear in humans near the eyes — “eyelids and under the conjunctiva (in such a case the worm can be easily observed, sometimes actively moving), subcutaneous tissues (nodules) in the chest wall, upper and lower limb, neck and in other body regions” such as the genitals.
Occasionally, the parasites can migrate to certain organs, such as the lungs, though it is less common, according to the ESDA guidelines.
The case report's lead author, Vladimir Kartashev, a professor in the Department of Infectious Diseases at Rostov State Medical University in Rostov-na-Donu, Russia, said in an email Thursday that such parasites are an “emerging disease” in the western part of the former Soviet Union and in certain parts of Europe. He said since 1997, there have been more than 4,000 human cases reported in these countries, particularly in Russia and Ukraine.
The CDC states D. repens — the species the woman in Russia had — is not seen in the United States; another species, D. tenuis, has been reported in North America but only in raccoons.
That said, the parasites usually die in the skin and are easily removed.
The case report said doctors in Russia surgically removed the worm from the woman's face, and she recovered. Well, at least physically.