A human case of a flesh-eating parasite, called New World screwworm, was reported in the U.S. this month, the U.S. Department of Health and Human Services said on Sunday.
The case involved a patient who returned to Maryland after traveling to El Salvador, HHS told Reuters. The Centers for Disease Control and Prevention confirmed the diagnosis on Aug. 4, the publication reported. It’s the first U.S. case linked to travel from a country with a current outbreak. Maryland health officials told The Associated Press that the patient has recovered and that no transmissions to other people or animals were found.
A New World screwworm infestation occurs when a NWS fly larva infests the living flesh of a warm-blooded animal, according to the CDC, which adds that female screwworm flies “lay their eggs on and in open wounds and mucous membranes,” and they can lay 200 to 300 eggs at a time.
The agency adds that the fly’s larva causes “extensive damage” by burrowing into its host’s tissue with “sharp mouth hooks.”
“The wound can become larger and deeper as more larvae hatch and feed on living tissue,” the CDC states. “As a result, NWS can cause serious damage to the animal or person it infests. Bacterial superinfection can also occur because of the NWS infestation.”
Livestock are most commonly affected, and infestations in humans, which the CDC describes as “very painful,” are rare. Countries in Central America and Mexico have reported recent cases of infestations in animals and humans, the agency states.
Overall, HHS spokesman Andrew G. Nixon told Reuters that “the risk to public health in the United States from this introduction is very low.”
The U.S. largely eradicated screwworm populations over 50 years ago by using the technique of breeding and dispersing sterile male screwworms to mate with female flies. U.S. Secretary of Agriculture Brooke L. Rollins announced earlier this month that the department will construct a sterile fly facility in Edinburg, Texas, to continue its efforts to eradicate the pest.
So, how concerned should we be about human cases of screwworm infestations?
Laurel Bristow, an infectious disease researcher at Emory University’s Rollins School of Public Health, told HuffPost that she doesn’t think the infestation case from the patient who returned from El Salvador “should give people a lot of concern about there being more cases in the United States right now.”
“We don’t currently have the fly in the United States,” she said, before pointing out that health officials are in contact with the person in Maryland, who will receive treatment.
“You just don’t want the flies to move through the larval stage in which they deposit themselves into soil in the United States, and then start to grow here,” she said. “So I think with this case it’s not particularly concerning that it will sprout more cases of the flies or of infestation.”
And even still, Bristow, a science communications influencer who hosts the radio show “Health Wanted,” emphasized that the “predominant, big concern is with livestock and with wild animals.”
Dr. Sheldon Campbell, an infectious diseases specialist and professor at Yale School of Medicine, told HuffPost that when it comes to concerns about more human cases of screwworm infestations, “there should be no spread in the U.S. following this case report.”
“The maggots would have to complete their life cycle in the patient, drop off, and mature into flies, find mates, and ultimately lay eggs in animals or people,” he said. “Though I didn’t see the details in the case report, this is pretty unlikely in a human patient.”
What are some good precautions to take when traveling to an area with a screwworm outbreak?
Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, told HuffPost that one should “cover any open wounds, avoid sleeping outdoors and use insect repellents.”
“The risk is primarily in areas in which the fly is present (close proximity to livestock) so rural areas are where [the] fly is more prevalent,” he said.
Campbell said that “prevention is key.”
“Keep open wounds clean and covered. Wear loose-fitting, long-sleeved shirts and pants, and socks to limit areas where you could get bitten,” he said. “Use an EPA-registered insect repellent.”
“Treat clothing and gear with products containing 0.5% permethrin,” he continued, before recommending that you “sleep indoors or in rooms with screens.”
Bristow said that overall, human cases of screwworm infestations are “still exceedingly rare,” so at this point she believes it’s sufficient to take the same precautions you would for preventing mosquito-borne diseases.
And Bristow emphasized, again, that “the real concern” with New World screwworm coming to the U.S. would be how it would impact livestock — “particularly the beef industry,” she said.
As for what signs of a screwworm infestation may look like in humans, Bristow said: “If you have a wound that is beginning to show signs of maggots, or getting bigger or not healing, that would be a good indication to go to the doctor.”
The CDC says that the only way to treat New World screwworms is to “physically remove the larvae from the infested tissue,” and that health care providers should remove larvae from the site.