By Cassandra GarrisonMEXICO CITY, Sept. 22 (Reuters) - A confirmed case of an animal infected with the flesh-eating screwworm parasite in Mexico's northern Nuevo Leon state near the U.S. border was immediately treated to prevent a further outbreak, the Mexican government said Monday. Fly traps in northern Mexico have not detected a single screwworm fly, the statement added. The infected animal was in a shipment of 100 animals originating from the Gulf Coast state of Veracruz, Mexico said. U.S. cattle ranchers on the southern border contacted by Reuters reacted with little surprise to the case in Nuevo Leon, and many have been preparing for months to deal with the pest. Mexican President Claudia Sheinbaum said the country was waiting on an assessment by a team of USDA experts that recently visited Mexico.