First US screwworm case in 60 years: Should America be worried?

The New World screwworm , a flesh‑eating parasite which infects cattle and other warm‑blooded animals, has been found in a calf in Texas, the US Department of Agriculture announced on Wednesday.

The screwworm is believed to have travelled from Central America to Mexico before being found in the calf in Texas, evading biological barriers that have kept the pest contained for decades, experts said. Screwworm was previously declared eradicated in the US in 1966.

Between mid-July and mid-August 2025, Mexico reported a 53 percent rise in the number of cases in animals. Humans can also be infected.

An outbreak in the US could heavily impact the livestock industry and cause increased beef prices. The USDA predicts that could cost the Texas economy $1.8bn in losses.

Here is why the first confirmed case in six decades is so concerning.

A screwworm comes from the larvae of a screwworm fly, also called Cochliomyia hominivorax and, yes, humans can be infected.

Female screwworm flies lay their eggs in scratches and wounds of warm-blooded animals, normally livestock or wild animals. The eggs hatch into hundreds of screwworm larvae which eat the living tissue of the infected animals.

The flies are attracted to the smell of open wounds on the bodies of these animals, or sometimes even of humans. Newborn calves are at high risk because the post-partum navel has yet to scar.