- U.S. battled a screwworm infestation decades ago.
- Agriculture Secretary Brooke Rollins closed the southern border to livestock imports.
- The New World screwworm can devastate any animal into which it burrows.
Because the New World screwworm has been detected in southern Mexico and is spreading north, the U.S. is halting live cattle, horse and bison imports from Mexico, on the orders of U.S. Department of Agriculture Secretary Brooke Rollins.
“The protection of our animals and safety of our nation’s food supply is a national security issue of the utmost importance,” Rollins said in a statement Sunday, noting the suspension would exist on a “month-by-month basis until a significant window of containment is achieved.”
The notice said that despite good-faith efforts of both the U.S. and Mexico to wipe out the screwworm, which has been described as a “flesh-eating maggot,” the deadly parasitic fly has spread northward.
Livestock already in holding to enter the U.S. will be processed normally, including a close inspection for the screwworm.
Rollins said she remains committed to opening the southern border again for livestock trade once eradication efforts have positive results.
The notice adds that the New World screwworm, often called simply NWS, could still get across the border through natural wildlife movements.
What is New World screwworm?
The fly larvae — maggots — burrow into the flesh of living animals and “cause serious, often deadly damage to the animal.” They can infest livestock, pets, wildlife, sometimes birds and “in rare cases,” people, per the announcement from the USDA.
The first case was reported to the U.S. last November and the border was shut down to live animal trade. In February, the two countries agreed to a “comprehensive pre-clearance inspection and treatment protocol" to protect the trade and contain the fly larvae spread.
The screwworm has already worked its way north through Panama and into Costa Rica, Nicaragua, Honduras, Guatemala, El Salvador and Belize, the notice said.
NPR reported that the maggots “feast on the flesh and blood of their host with tiny mouth hooks. Left untreated, the parasitic infection can kill a full-grown cow within one to two weeks. Efforts to get rid of the pest go back many decades.”
USDA’s Animal and Plant Health Inspection Service is releasing sterile flies in strategic locations in southern Mexico and Central America. The inspection service calls the screwworm a “devastating pest.”
According to that agency, the adult screwworm flies are about the size of common houseflies, and have orange eyes, a metallic blue or green body and three dark stripes along their backs.
Mammals and birds that have been infected can show this type of behavior:
- Irritated behavior
- Head shaking
- Decay smell
- Evidence of a fly strike
- Visible maggots in wounds
Eradicating New World screwworm
In the 1960s, the U.S. and Mexico got rid of the screwworm exactly as they’re hoping to do now, by releasing a huge number of sterile adult flies to mate with the females, who will then not produce viable eggs.
NPR said that in 1976, a Texas outbreak affected 1.4 million cattle and hundreds of thousands of sheep and goats.
The USDA said the detection in southern Mexico is on farms about 700 miles from the U.S. border.
Reuters in April reported the first human case of illness caused by screwworm in Mexico. The woman, 77, was treated successfully with antibiotics and was in stable condition.
The journal BMJ noted at least 30 human cases in Nicaragua and at least 28 in Costa Rica.