In a critical development for veterinary professionals across all practice types, the U.S. Department of Agriculture (USDA) has released a comprehensive training module to help identify and respond to New World screwworm (NWS) as the parasitic pest moves dangerously close to the U.S.-Mexico border.
The training resource, “Module 41: New World Screwworm: A 21st Century Perspective,” was released in early April and provides essential information on recognizing signs of infestation, understanding the parasite’s life cycle, implementing control measures, and properly reporting suspected cases.
“In terms of prevention, you are our first line of defense as you very well may be the first one to see an NWS larvae that’s entered the country,” explains the module narrator, highlighting the crucial role veterinary professionals play in early detection.
Why Immediate Action is Critical
The potential impact of an NWS infestation in the United States cannot be overstated. The training emphasizes the alarming reproductive capacity of these parasites—a single female can lay up to 3,000 eggs during her short lifespan of 10-30 days, with each batch containing 200-300 eggs.
Unlike common external parasites in dogs, screwworm larvae feed on living tissue rather than dead matter, causing severe wounds that can be fatal if untreated. This makes early detection absolutely critical.
Signs Veterinary Professionals Should Look For
The USDA training module advises all veterinary professionals to watch for these key indicators:
Infestations often begin at pre-existing wounds, even those as small as tick bites
Common infection sites include mucous membranes—nostrils, eyes, ears, mouth, and genitalia
By the third day, larvae (2mm to 1.5cm long) become visible in wounds
Affected animals may display irritated behavior, head shaking, isolation, rubbing against objects, standing in water, and wounds may emit a distinctive odor of decay
Reporting Protocols
If NWS is suspected, USDA-accredited veterinarians must notify both their state animal health official and a USDA veterinary officer immediately. The after-hours reporting line is (866) 536-7593.
When directed to submit samples, veterinary professionals should collect maggots from all areas of the wound, including the deepest parts.
The Northward Spread
The urgent need for vigilance comes as NWS has breached Panama’s Darien Gap—previously a biological barrier—and moved rapidly northward. According to USDA data, cases in Panama exploded from an average of 25 annually to more than 6,500 in 2023 alone.
The parasite has continued its march through Central America and into Mexico, prompting temporary suspension of cattle and bison imports until new inspection protocols were established in February.
Of particular concern, Nicaragua’s health ministry has confirmed at least 30 human cases, with two patients requiring lifesaving hospital treatment.
“If NWS makes its way to the U.S., our means of control will be effective, but are costly and take time,” the training module warns.
The USDA is collaborating with multiple agencies, including the U.S. State Department and the Food and Agriculture Organization of the United Nations, to respond to the outbreak and prevent its spread into the United States.
For additional resources, the USDA has made available a brochure on New World screwworm and standard operating procedures for possible detection in dogs and other animals.