Screwworm? What’s the flesh-eating parasite found in a human in the US?

The United States has reported its archetypal quality lawsuit of New World screwworm, according to its Department of Health and Human Services (HHS).

The flesh-eating parasite usually eats cattle and different warm-blooded animals, and is fatal if near untreated.

The case, investigated by the US Centers for Disease Control and Prevention (CDC), was confirmed connected August 4 and progressive a diligent who returned from El Salvador to the US authorities of Maryland, HHS spokesperson Andrew Nixon said successful an email to the Reuters quality agency.

Nixon did not code an earlier study that said a lawsuit had been confirmed successful Maryland successful a idiosyncratic who had travelled from Guatemala. The US authorities has not confirmed immoderate cases successful animals truthful acold this year.

What’s a screwworm?

It’s the larva of a screwworm fly.

Female screwworm flies laic their eggs successful the wounds of warm-blooded animals, and those eggs hatch into hundreds of screwworm larvae.

The larvae past usage their crisp mouths to burrow done the surviving soma of their hosts for astir a week.

At the extremity of that week, they driblet to the ground, signifier a pupa and make successful the crushed for different week to 2 months earlier emerging arsenic an big fly.

Screwworm tin beryllium devastating successful cattle and wildlife and has been known to infect humans.

A calf sprayed with disinfectant to forestall screwworm arsenic the Mexican authorities and ranchers conflict to power the spread, successful Tuxtla Gutierrez, Chiapas, Mexico, connected July 3, 2025 [Daniel Becerril/Reuters]

What are the symptoms?

Screwworm infestations successful wildlife and humans origin painful, progressive wounds arsenic larvae burrow into surviving tissue. Symptoms see open, foul-smelling sores that enlarge rapidly, with disposable maggots inside.

Affected animals whitethorn amusement weakness, reduced mobility, value loss, and abnormal behaviour from distress. In humans, symptoms see terrible pain, swelling, fever, and secondary infections.

Screwworm is diagnosed chiefly by ocular recognition of larvae successful wounds. The maggots person distinctive features, specified arsenic acheronian tracheal tubes disposable done their bodies with bands of spines astir each segment.

If untreated, infestations tin pb to insubstantial demolition and adjacent death.

How is it treated?

Painfully.

The hundreds of larvae person to beryllium manually removed, and the wounds disinfected.

Antibiotics are often prescribed to power secondary bacterial infections, and symptom absorption whitethorn beryllium indispensable successful terrible cases.

In animals, topical oregon systemic insecticides are besides utilized to termination remaining larvae and forestall re-infestation.

With thorough care, betterment is possible, but untreated cases tin pb to extended insubstantial harm and death.

Why is this lawsuit significant?

As big screwworm flies are susceptible of travelling galore kilometres successful hunt of hosts, infestations tin dispersed rapidly crossed wildlife populations, livestock herds and adjacent to humans. The diligent successful Maryland represented the first-ever recorded lawsuit of quality screwworm successful the US.

In summation to the imaginable quality wellness toll, the dispersed of the parasite could besides rattle the US cattle industry. In particular, newborn calves are astatine precocious hazard due to the fact that the post-partum navel has yet to scar.

Beef producers and livestock traders successful the US are already connected alert for imaginable infestations, arsenic screwworms person precocious been recovered moving northbound from Central America into confederate Mexico.

What are governments doing astir it?

The US government’s confirmation of a screwworm lawsuit comes conscionable much than a week aft US Department of Agriculture (USDA) Secretary Brooke Rollins travelled to Texas to denote plans to physique a sterile alert installation determination arsenic portion of efforts to combat the pest.

A sterile alert installation produces a ample fig of antheral flies and sterilises them. These are past released to mate with females successful the wild, which reduces the chaotic colonisation implicit time. This method eradicated screwworm from the US successful the 1960s.

The USDA has estimated that a screwworm outbreak could outgo the system successful Texas, the largest cattle-producing state, astir $1.8bn successful livestock deaths, labour costs and medicine expenses.

Earlier this year, Mexico besides began efforts to bounds the dispersed of the pest by kicking disconnected operation of its ain $51m sterile alert accumulation facility.

Larvae of the screwworm fly, collected from infected cows, astatine the COPEG sterile alert accumulation works successful Pacora, Panama, connected June 11, 2025 [Enea Lebrun/Reuters]

Why is the US cattle manufacture nervous?

Screwworms person been travelling northbound done Mexico from Central America successful caller years.

They are endemic successful Cuba, Haiti, the Dominican Republic and countries successful South America, according to the USDA.

When Mexico reported a caller lawsuit astir 595km (370 miles) southbound of the US borderline successful July, the USDA ordered the closure of livestock commercialized done confederate ports of entry, aft antecedently halting imports successful November and May.

The US legally imports much than a cardinal heads of cattle from Mexico a year, utilized to fatten feedlots and for slaughtering.

But amerciable cattle smuggling, agelong considered 1 of the astir businesslike money-laundering means for Central American cause cartels, is present regarded arsenic the main imaginable menace for the beforehand of the parasite successful the US.