FILE PHOTO: Larvae of the screwworm fly, collected from infected cows, are observed at the COPEG sterile fly production plant, which fights the spread of the cattle screwworm, in Pacora, Panama, June 11, 2025. REUTERS/Enea Lebrun/File Photo
FILE PHOTO: A view shows a calf after being sprayed with a disinfectant spray to prevent screwworm as the Mexican government and ranchers struggle to control the spread of the flesh-eating screwworm, in Tuxtla Gutierrez, Chiapas state, Mexico July 3, 2025. REUTERS/Daniel Becerril/File Photo

By Cassandra Garrison

MEXICO CITY (Reuters) -Mexico saw a nearly 32% increase in confirmed cases of the flesh-eating screwworm parasite, according to the latest monthly government data, as a concentration of cases moves north.

Mexico recorded 6,703 cases of animals infested with New World screwworm as of September 13 since the start of the outbreak in November of last year. That was compared to 5,086 confirmed cases during the previous period, which ended August 17.

The latest report by sanitation agency Senasica, which was published on September 26 and seen by Reuters on Wednesday, shows the outbreak is becoming more concentrated as it moves northward through Mexico.

Of the total cases, 5,258 were confirmed in cattle.

The spread of screwworm as it moves closer to the U.S. border has sparked a diplomatic spat between the two trading partners as the U.S. casts blame on Mexico for not doing enough to contain the parasite, which infests and can kill livestock if untreated. The U.S. government has kept its border mostly closed to Mexican cattle imports since May.

There were five confirmed cases in Puebla state for the first time, which is about 80 miles (129 km) from capital Mexico City. There were also 744 cases in Oaxaca state, compared to 453 in the August report.

Veracruz state saw cases nearly double to 476 from 252 a month earlier. Chiapas state, which borders Guatemala, remains the area most affected by the outbreak, with 3,474 confirmed cases, up from 2,875 in August.

Mexico confirmed a case of screwworm in an animal in Nuevo Leon state on September 21, which borders the U.S., and said it was immediately treated to prevent a further outbreak.

In August, the U.S. confirmed its first human case in the United States of travel-associated screwworm from an outbreak-affected country, after Reuters exclusively reported on the case. The last major outbreak of screwworm in the U.S. was from 1972 to 1976 across six states.

The U.S. government shut down much of its operations on Wednesday after Congress and the White House were unable to reach a funding deal, leading to the furlough of about 42,000 USDA staff, roughly half the agriculture agency's employees.

The agency is expected to use emergency funds to continue animal health programs related to diseases like bird flu and screwworm, according to the agency's 2025 shutdown contingency plan.

(Reporting by Cassandra Garrison; editing by Stephen Eisenhammer and Bill Berkrot)