‘That barrier has been breached’: Infectious diseases doctor warns travellers about flesh-eating parasite

The composite image shows the following: an ulcer from a New World screwworm infestation on the right shin (A), larvae removed from the ulcer (B), and posterior spiracles of larvae (C). (Travel Medicine and Infectious Disease)

They may be small, but New World screwworm maggots can burrow or screw into the wounds of living things – including humans in rare cases – and seriously hurt and even kill them.

Infectious diseases specialist Dr. Isaac Bogoch is warning Canadian travellers about the flesh-eating parasite after he says the barrier preventing it from spreading north of Panama was “breached.”

New World screwworm (NWS), or Cochliomyia hominivorax, is commonly found in Cuba, Haiti, the Dominican Republic and South American countries, according to the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) in a post on its website dated March 3.

Cases are now spreading north to Costa Rica, Nicaragua, Honduras, Guatemala, Belize, El Salvador and Mexico, it added.

To stop the parasite from moving to normally screwworm-free areas in Central and North America, the APHIS has worked with Panama to maintain a “biological barrier” zone in the eastern part of the country, which prevented cases from spreading for decades.

Bogoch said the “barrier” should be recreated because it’s not only a public health issue – it also affects food security. “This infection can decimate wildlife and livestock,” the infectious diseases specialist at Toronto General Hospital told CP24 Breakfast on Tuesday.

Bogoch’s warning comes after a flesh-eating parasite infected a Canadian traveller who recently returned from Costa Rica. The country declared a screwworm national emergency in February.

Bogoch described how the infected fly can lay eggs on wounds, which turn into maggots or larvae that then eat the tissue, causing significant damage with the potential to kill humans and animals.

The maggots tear into the host’s tissue “with sharp mouth hooks,” causing the wound to become larger and result in more maggots, according to APHIS.

“It’s gross – you have like a larva coming out of a wound on your body and they just have to be extracted,” Bogoch said. “We didn’t normally see this anywhere north of Panama because there’s this very smart program to keep this from moving northward.”

Bogoch said the program involves the release of millions of sterilized flies in areas where infected flies may be. If an infected fly mates with a sterilized fly, even if that infected fly travels north, the eggs it lays won’t hatch, he added.

“So there’s been this amazing barrier preventing this infection from moving northward,” Bogoch said. “However, that barrier has been breached and we’re starting to see cases north of Panama, especially in Costa Rica and Nicaragua.”

Can we prevent screwworm infections?

Bogoch said there are no vaccines or anything to prevent people from getting infected. “It really has a knack for laying eggs on scrapes and scratches that people have,” he said.

Bogoch advises people to seek medical advice before travelling.

“People could be travelling to areas with different diseases that you might not be aware of and there might be simple steps you can take to stay safe while travelling,” he said.