Screwworm spreads in Mexico, raising alarm across north America

MEXICO CITY: A dangerous flesh-eating parasite known as the New World screwworm is spreading through parts of Mexico and Central America, with hundreds of human infections reported and growing concern over its potential impact on livestock and animal health.

The parasite is the larval stage of a particular fly. Unlike ordinary flies, the female screwworm fly can lay eggs in open wounds or vulnerable areas of living animals and humans. The eggs can hatch within about a day, after which the larvae enter the wound and feed on living tissue.

The infection, known as myiasis, can become severe if treatment is delayed. In serious cases, the larvae can damage muscles and even reach deeper tissues and bones.

A study published in a medical journal linked to US health authorities examined 202 confirmed human cases recorded in Mexico between April 2025 and March 2026. Researchers found that reported infections increased sharply, rising from roughly three cases a week in 2025 to more than nine cases a week during 2026.

More than half of the patients examined had infections involving their legs. Other cases affected the head, neck, nose, mouth and eyes, highlighting the parasite’s ability to invade different parts of the body through wounds or vulnerable tissue.

The study reported six deaths among the patients examined, although researchers directly linked only one of those deaths to screwworm infection.

The average age of patients was about 61, while 72 per cent were men. Researchers also found that 77 per cent of those infected had at least one pre-existing medical condition, potentially increasing their vulnerability to complications.

The parasite is considered particularly dangerous for livestock because its larvae feed on living tissue. Untreated infections can cause serious wounds, weaken animals and, in severe cases, prove fatal.

The resurgence has also raised concerns in the United States. The country had previously eliminated the New World screwworm after decades of control efforts, achieving eradication in 1966.

However, the parasite returned to the spotlight after an infected calf was confirmed in Texas’s Zavala County in June 2026, according to international reports.

The development has heightened fears that the parasite could spread further north, particularly through livestock movement and other routes.

Health and agricultural authorities face the difficult task of controlling the parasite while detecting infections early. For people, experts generally stress the importance of seeking medical attention for unusual or worsening wounds, particularly after exposure in areas where screwworm is circulating.

The outbreak serves as a reminder that a tiny insect can create a major public-health and agricultural challenge when conditions allow a dangerous parasite to spread.