Human screwworm case poses no risk to agriculture, says USDA official

By Tom Polansek and Leah Douglas

DECATUR, Illinois, Aug 26 (Reuters) - The human case of screwworm reported this week by U.S. health officials is the country's only one so far this year and poses no risk to the farm sector, a U.S. Department of Agriculture official said on Tuesday.

Screwworm, a flesh-eating parasite that eats its hosts alive, has moved northward through Central America and southern Mexico, putting the U.S. cattle industryon high alert.

A screwworm infestation can be fatal to livestock if untreated. An outbreak could cost the economy of Texas, the top cattle-producing state, nearly $2 billion, according to U.S. estimates.

The human case in a person who had traveled from El Salvador to Maryland was confirmed by the U.S. Centers for Disease Control and Prevention on August 4, but the agency did not publicly disclose it until Reuters exclusively reported on the case on August 24. The affected person fully recovered and there was no sign of spread to other people or animals, Maryland state health officials told Reuters.

In the USDA's first remarks on the subject, Deputy Secretary Stephen Vaden said on Tuesday at the Farm Progress Show in Decatur, Illinois, that the agency had only recently learned of the case.

"I don’t know the exact date that she learned about it, but we found out about it I think it was over the weekend," he said, referring to Agriculture Secretary Brooke Rollins.

When asked why the case was not announced sooner, Vaden said he was not familiar with the CDC's notification process and added that the human case poses no risk to U.S. agriculture.

Following Vaden's comments, the USDA released a statement late on Tuesday, saying the CDC has been leading the response to the human case. In support of that response, the USDA initiated targeted screwworm surveillance in a 20-mile (32 km) radius including parts of Washington, D.C., Maryland and Virginia, which had so far not detected the pest.

The release did not clarify when the agency learned of the human case or initiated its surveillance. The USDA did not immediately respond to a request to clarify the sequence of events or whether Rollins has communicated with CDC about the case.

The release also said the risk to U.S. public health from the human case is very low and that there have been previous travel-associated human cases of screwworm. The USDA has not detected screwworm in livestock or other animals since 2017, the release said.

Conservation and cattle groups previously told Reuters that the CDC's delay in publicly reporting the case erodes trust between producers and government agencies.

The USDA is investing $750 million to build a Texas facility that would produce and distribute sterile flies to mate with the wild screwworm population and drive down their numbers.

Vaden said the plant will open in about 18 months. Rollins previously said it could take two to three years for such a facility to come online.

Animal health experts have told Reuters that a number exponentially greater than the current supply of sterile flies would be needed to stop the spread of screwworm.

The USDA has also been working closely with Mexican officials to combat the spread of the pest, though the U.S. decision to keep its border mostly closed to Mexican cattle imports since May has injected some fresh tension into the countries' ongoing trade deal negotiations.

There is still no timeline to reopen the border, and the USDA is sending a team to Mexico in two weeks to verify that Mexico is following protocol to prevent screwworm's northern spread, Vaden said.