Dr. warns Canadians: Flesh-eating parasite outbreak in Central America, Mexico
This parasite is not currently found in Canada, but with travel-related cases increasing, Canadians heading south should be on alert.
A recent outbreak of a flesh-eating parasite known as the New World screwworm (Cochliomyia hominivorax) has triggered a public health emergency in Costa Rica, and experts are warning Canadian travellers to take precautions.
Infectious disease specialist Dr. Issac Bogoch recently took to X to spread awareness and is warning Canadians, especially those travelling to destinations like the Dominican Republic, Costa Rica, and Mexico.
What is the New World Screwworm (NWS)?
Despite what its name suggests, the New World screwworm is not a worm at all—it is a species of parasitic fly.
Female screwworm flies lay their eggs in open wounds, scrapes, or insect bites on people and animals. When the eggs hatch, the larvae burrow into the flesh, feeding on living tissue and potentially causing serious wounds, infections, and even death if left untreated.
Infections occur primarily in livestock but people can and do get infected, including an 80-year-old Canadian male traveller who went to a Toronto hospital with an NWS infection (also called myiasis) after visiting Costa Rica.
Speaking with CP24, Dr. Bogoch said NWS is a public health issue that can also impact food security.
“This infection can decimate wildlife and livestock,” he told the news outlet.
How do people get infected with NWS?
According to the U.S. Centers for Disease Control and Prevention, you can become infected if:
You travel to affected areas (like Costa Rica, Nicaragua, or Mexico);
You have open cuts, sores, or scratches;
You come into contact with livestock or wildlife carrying the parasite.
Preventing infection
Canadian travellers can protect themselves by:
Covering any cuts or scratches with clean, dry bandages;
Using insect repellent, especially on exposed skin;
Wearing long sleeves and pants in rural areas or places with plants and trees;
Avoiding close contact with stray animals or livestock;
Consulting a travel health clinic and a medical professional before travelling.
There are no vaccines or medications that prevent infection.
If you suspect infection:
Seek medical attention immediately.
Do not attempt to remove larvae yourself.
Treatment usually involves the extraction of the larvae and prescription antibiotics.
Why is NWS becoming a problem?
NWS is commonly found in Cuba, Haiti, the Dominican Republic, and South American countries but the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) says cases are spreading to Costa Rica, Nicaragua, Honduras, Guatemala, Belize, El Salvador and Mexico, beyond a biological border that had previously contained the spread.
The agency says there has been an "explosion" in NWS detections in Panama. In 2023 cases went up from an average of 25 cases annually to more than 6,500 cases in one year.
(APHIS/USDA.gov)
Costa Rica, Mexico declare NWS outbreak after 'barrier' breached
Health agencies are raising the alarm because the spread of NWS has breached the barrier the APHIS and Panama co-managed that "successfully" contained the pest in South America for "decades," APHIS says on its website. The barrier, now breached, is in the eastern portion of Panama.
The outbreak declarations in Costa Rica and Mexico have triggered emergency responses in the United States, Mexico, and Costa Rica, which first declared an NWS emergency in February.
NWS was eradicated from the U.S. in 1966, but officials remain on alert for re-introduction.
On its website, APHIS says it is partnering with other USDA agencies, including the U.S. Department of State, the Food and Agriculture Organization of the United Nations, and affected countries to combat the outbreak.
"APHIS is investing $109.8 million to combat new NWS detections in Central America and Mexico to keep the pest from spreading into North America," the agency says.
"With this funding, APHIS aims to eradicate NWS in Central America and Mexico and re-establish the biological barrier."
Can NWS survive in Canada?
The parasite typically needs warm conditions to survive and Canada's cooler climate acts as a natural barrier.
This parasite is not currently found in Canada, but with travel-related cases increasing and the barrier that once stopped its spread now breached, Canadians heading south should be on alert.
Always check travel health advisories and when in doubt, speak to a medical professional before travel.
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Header image: Cheryl Santa Maria for The Weather Network.