The resurgence of the deadly screwworm in the US has raised serious concerns about livestock health, food security, and public safety. After the first human case was confirmed in Maryland in August 2025, questions are swirling about how the US is responding to this ancient parasite's return. Below, we explore what a screwworm is, how it reached the US, and what measures are being taken to prevent a full-blown outbreak.
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What is a screwworm and why is it dangerous?
A screwworm is a parasitic fly whose larvae burrow into the flesh of warm-blooded animals, including humans and livestock. It causes severe tissue damage and can lead to infections if untreated. Historically eradicated in the US, the screwworm has now reemerged in Central America and Mexico, posing a threat to the livestock industry and public health.
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How did the screwworm reach the US?
The screwworm has been spreading northward through Central America and Mexico since 2023. The recent case in Maryland involved a person returning from El Salvador, indicating the parasite's movement across borders. Its ability to hitchhike on animals and humans makes containment challenging, especially with increased travel and trade.
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What measures are being taken to prevent an outbreak?
The US is constructing an $8.5 million sterile fly facility in Texas to produce sterile screwworms that will outcompete and reduce the wild population. Additionally, livestock imports from Mexico have been suspended, and authorities are monitoring the situation closely to prevent the parasite from establishing itself further.
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Could this affect livestock and the food supply?
Yes, the screwworm poses a significant threat to livestock, which could lead to economic losses and impact food security. Mexico has already suffered losses of over $1.3 billion in cattle exports. The US aims to prevent similar damage by controlling the parasite before it spreads widely.
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Is the screwworm a new problem for the US?
While the screwworm was eradicated in the US in the 1960s, its recent resurgence in Central America and Mexico has brought it back into focus. The Maryland case is a wake-up call, prompting renewed efforts to protect US agriculture and public health from this parasitic threat.
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How can people protect themselves from screwworms?
Individuals should avoid contact with infected animals and seek medical attention if they notice flesh wounds that do not heal. Early detection and treatment are crucial, especially for travelers returning from regions where screwworms are present. Public health officials are also increasing awareness to prevent underdiagnosis.