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

The US Department of Agriculture says New World screwworm has been detected in a Texas calf.

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.

The larvae use their sharp mouths to burrow through the living flesh of their hosts for about a week.

Then they drop to the ground, form a pupa and develop in the ground for another week to two months before emerging as an adult fly.

Screwworm can be devastating in cattle and wildlife which can die from infection if untreated.

As adult screwworm flies are capable of travelling many kilometres in search of hosts, infestations can spread quickly across wildlife populations, livestock herds and between humans.

Dr Timothy Goldsmith, a veterinary medicine professor at the University of Minnesota, told Reuters that homeless people can be especially vulnerable to infestation because they sleep outside and have less access to hygiene products and medical care.

It is rare for people to catch screwworm, however, and they cannot be infected by New World screwworm from eating normal, inspected, cooked beef.

Last year, Mexico confirmed 41 human cases, primarily in the state of Chiapas, according to Mexican media.

Screwworm infestations in wildlife and humans cause painful, progressive wounds as larvae burrow