New World Screwworm: Overview and Current Concerns

What Is the New World Screwworm?

Biological Profile

The New World screwworm is a parasitic fly species scientifically known as Cochliomyia hominivorax. Its larvae infest open wounds and natural body openings of warm-blooded animals, including humans. Unlike most fly larvae that feed on dead tissue, screwworm larvae consume living flesh, making them particularly destructive Source 3.

Distinction from Other Flies

Screwworm larvae specifically target living hosts, causing a condition called myiasis. This sets them apart from common blowflies whose maggots typically consume decaying matter Source 1.

Geographic Distribution and Recent Outbreaks

Historical Context

The pest was previously eradicated from the United States and is now primarily found in parts of Central and South America.

Current Situation (2025–2026)

Active outbreaks have been reported in Mexico and Central America. A recent detection occurred approximately 31 miles from the U.S. border, and the first confirmed U.S. human case was announced in August 2025 Source 7.

Impact on Livestock and Human Health

Economic Threat to Agriculture

An outbreak could cause millions of dollars in livestock damage, posing a severe risk to cattle and other animals Source 7.

Human Health Considerations

Human infections are rare but can be serious. Larvae may infest wounds, eyes, ears, nose, mouth, or genitals. The recent U.S. case was linked to international travel, and the overall domestic risk remains low Source 10.

Prevention and Control Measures

Early Detection Strategies

Livestock owners should regularly inspect animals for wounds and monitor for unusual fly activity.

USDA APHIS Guidelines

The USDA continues surveillance, sterile insect release programs, and border monitoring to prevent re-establishment Source 2.

FAQ

What exactly is a screwworm and how does it differ from common maggots? Screwworm larvae feed exclusively on living tissue, whereas most maggots consume dead or decaying matter.

How serious is the current threat to U.S. livestock? The pest poses significant economic risk if it spreads, with potential losses in the millions.

Can humans contract New World screwworm? Yes, though cases are rare and typically linked to travel rather than local transmission.

What should livestock owners do to protect their animals? Inspect animals frequently, treat wounds promptly, and report suspected cases to authorities.

Is there a risk of local transmission within the United States? Current evidence suggests the risk remains low.

What prevention methods does the USDA recommend? Surveillance, sterile insect technique, rapid response, and public education on wound care.