Maggots from screwworm flies burrow into the flesh of living animals, causing serious damage. While it can often be fatal, infected animals can be treated by removing larvae and applying medications, if it is detected early enough.

The infestation, which began in November, has now claimed its first human casualty: an 86-year-old woman with advanced cancer and complications from a screwworm infection who died in the state of Campeche in late July. While infections are rarer (and treatable) in humans, Mexico confirmed more than 30 cases in people in the last week of July.

Estimates cited by Mexican authorities in 2022 and others by sector experts indicate the number of illegal cattle crossing into Mexico is at least 800,000 per year.