First US human case of flesh-eating screwworm parasite confirmed as outbreak spreads in Mexico

USA – The United States has confirmed its first human case of New World screwworm infestation, a flesh-eating parasitic disease, in a patient who recently returned from El Salvador, health officials announced this week.

The U.S. Department of Health and Human Services (HHS) said the case was confirmed on August 4 and marks the country’s first travel-associated human infection of New World screwworm (NWS) myiasis. 

The Centers for Disease Control and Prevention (CDC) and Maryland health authorities jointly investigated the patient, who has since received treatment.

“This is the first human case of travel-associated NWS myiasis from an outbreak-affected country identified in the US,” HHS spokesperson Andrew Nixon said in a statement.

The parasite, found primarily in South America and the Caribbean, has steadily spread northward in recent years. Since 2023, confirmed outbreaks have been reported in every Central American country, as well as in Mexico.

Mexico faces surge in animal and human cases

Mexico has recorded a 53% rise in screwworm cases over the past month, reporting more than 5,000 infestations in cattle and other animals, according to government data cited by Reuters. 

As of August 17, 649 active cases were ongoing, with 41 human infections confirmed in the past year, primarily in Chiapas state.

The outbreak has already inflicted steep economic damage. The Mexican National Agricultural Council estimates livestock export losses of US$1.3 billion over the past year. 

The parasite has also disrupted U.S.-Mexico cattle trade, with Washington suspending some imports over fears the infestation could spread across the border.

The U.S. Department of Agriculture (USDA) has warned that a widespread outbreak could endanger more than US$100 billion in economic activity linked to the cattle and livestock industry.

“When NWS fly larvae (maggots) burrow into the flesh of a living animal, they cause serious, often deadly damage to the animal,” USDA said. “NWS can infest livestock, pets, wildlife, occasionally birds, and in rare cases, people.”

Global agencies push for coordinated response

The World Organisation for Animal Health (WOAH) has called for stronger international cooperation to curb the spread. 

In an August 22 statement, the organisation urged countries to intensify surveillance, improve cross-border collaboration, and strengthen diagnostic capacity.

“The prevention and control of this parasitic zoonotic disease is challenging and requires long-term coordinated efforts by affected and at-risk countries,” WOAH said.

Control measures rely on sterile insect technique programs, where sterilised male flies are released to reduce reproduction in the wild. Facilities in Chiapas, Texas, and Panama are now tasked with producing about 500 million sterile flies weekly to push the parasite back toward South America.

Meanwhile, HHS has approved emergency veterinary drugs to help protect U.S. herds. “The risk to human health in the United States remains very low, but the potential future threat to animal populations and the food supply chain requires proactive action,” the department said.

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