Everything You Need to Know About the Flesh-Eating New World Screwworm

The New World screwworm (*Cochliomyia hominivorax*), a parasitic fly notorious for its flesh-eating larvae, has re-emerged as a concern in the United States with the first human case in decades reported in Maryland in August 2025. This alarming development, coupled with its potential to devastate livestock, has raised red flags among public health officials and the agricultural sector. Below is a comprehensive guide to understanding the screwworm, its implications, and the ongoing response to curb its spread.

What is the New World Screwworm?

The New World screwworm is not a worm but a species of parasitic fly native to parts of South America, Central America, and the Caribbean. Unlike typical maggots that feed on dead tissue, screwworm larvae burrow into the living flesh of warm-blooded animals, including cattle, wildlife, pets, and, in rare cases, humans. The name "screwworm" comes from the larvae’s corkscrew-like burrowing pattern, which can cause severe pain, tissue damage, and potentially fatal infections if untreated.

Life Cycle and Behavior

- Egg Laying: Female screwworm flies lay up to 200–3,000 eggs in open wounds, cuts, or natural body openings (e.g., nose, mouth, or eyes) of warm-blooded hosts.
- Larval Stage: After hatching, larvae feed on living tissue, burrowing deeper and causing significant damage. This stage, known as myiasis, can lead to secondary bacterial infections.
- Maturation: After feeding for several days, larvae drop to the ground, burrow into the soil, and emerge as adult flies, perpetuating the cycle.
- Impact: In livestock, infestations often target wounds from branding, dehorning, or childbirth, leading to high mortality rates if untreated. In humans, symptoms include a sensation of movement in the wound, severe pain, and visible larvae.

Human Cases

Human infections, though rare, are gruesome. The Maryland case involved a traveler returning from Central America (reports conflict between El Salvador and Guatemala as the origin). The patient was treated successfully through manual removal of larvae and wound disinfection, with no evidence of transmission to others. The Centers for Disease Control and Prevention (CDC) confirmed the diagnosis on August 4, 2025, marking the first U.S. human case since the 1960s. Public health risk remains low, as screwworms do not spread like contagious diseases.

Historical Context: A Once-Eradicated Threat

The U.S. successfully eradicated the New World screwworm in 1966 using the Sterile Insect Technique (SIT), a groundbreaking method where sterilized male flies are released to mate with wild females, producing non-viable eggs and collapsing the population. This approach eliminated screwworms from the U.S. and much of Central America, with a containment line maintained in the Darien Gap between Panama and Colombia.

However, since 2023, screwworms have been spreading north from Central America through Mexico, with cases reported as close as 370–400 miles from the U.S. border in Veracruz. This resurgence, possibly driven by climate change, globalization, and increased human-animal contact, has reignited concerns.

The Maryland Case: A Wake-Up Call

In August 2025, a Maryland resident who had traveled to Central America was diagnosed with screwworm myiasis, the first U.S. human case in over 60 years. The patient, treated successfully, likely contracted the parasite abroad, as screwworms are not currently established in the U.S. The case, confirmed by the CDC, sparked criticism over communication delays, with some veterinarians and beef industry stakeholders learning of it informally rather than through official channels.

The discrepancy over the patient’s travel origin (El Salvador vs. Guatemala) remains unresolved, with the U.S. Department of Health and Human Services (HHS) citing El Salvador. Maryland’s status as a sanctuary state has fueled speculation about the patient’s background, though no immigration details were disclosed due to privacy laws.

Impact on the Cattle Industry

The screwworm poses a far greater threat to livestock than humans. Cattle are particularly vulnerable, as larvae target wounds from routine practices like branding or minor injuries. A Texas A&M University estimate suggests a Texas outbreak could cost the beef industry $1.8 billion due to livestock deaths, treatment costs, and market disruptions. With the U.S. cattle herd at its smallest in 70 years and beef prices at record highs, an outbreak could exacerbate food price inflation and strain feedlot margins.

The parasite’s northward spread has already prompted the USDA to suspend cattle imports from Mexico multiple times, including after a July 2025 case in Veracruz. These trade restrictions, while necessary for biosecurity, further stress an already fragile cattle market.

USDA and Global Response

The USDA is taking aggressive measures to prevent screwworm re-establishment in the U.S.:

- Sterile Fly Facility in Texas: USDA Secretary Brooke Rollins announced plans for a new facility at Moore Air Force Base in Edinburg, Texas, to produce up to 300 million sterile flies weekly. Construction will take 2–3 years.
- Current Capacity: The only existing sterile fly plant, in Panama City, produces 100 million sterile flies per week, but experts estimate 500 million are needed weekly to push screwworms back to the Darien Gap.
- Mexico’s Efforts: Mexico is building a $51 million sterile fly facility in its southern region to complement regional containment efforts.
- Border Surveillance: Enhanced trapping stations, synthetic lures, and detection dogs are being deployed to monitor and prevent screwworm entry. Cattle import bans from affected regions remain in place.

These measures build on the success of past SIT campaigns but face challenges due to the scale required and the time needed to operationalize new facilities.

Broader Implications: Biosecurity and Beyond

The screwworm’s return highlights broader biosecurity vulnerabilities. Climate change is expanding the range of disease vectors like flies and ticks, while globalization facilitates the rapid spread of pathogens. Increased human-animal contact, driven by habitat encroachment, further elevates risks of zoonotic diseases.

Some speculate about the potential for screwworms to be weaponized as an agroterrorism tool, especially given recent cases of smuggled pathogens. While no evidence supports this in the Maryland case, the USDA classifies screwworms as an agricultural biosecurity threat, underscoring the need for vigilance.

The Good News

Despite the alarming nature of screwworm infestations, there are positive developments:
- Low Public Health Risk: Human cases are rare, treatable, and not contagious. The Maryland case was isolated, with no reported transmission.
- Proactive Measures: The USDA’s investment in sterile fly technology and border controls aims to prevent a wider outbreak.
- Cattle Cycle Rebound: Industry leaders predict a cattle herd rebuild starting in 2026, which could mitigate long-term economic impacts if screwworms are contained.

Conclusion

The New World screwworm’s re-emergence, marked by the Maryland case, serves as a stark reminder of the fragility of biosecurity systems. While the public health threat remains low, the potential economic devastation to the cattle industry demands urgent action. The USDA’s multi-pronged response, including new sterile fly facilities and enhanced border measures, aims to replicate past eradication successes. However, with climate change and globalization fueling the spread of such pests, sustained vigilance and international cooperation are critical to protecting both agriculture and public health.

Sources:
1. Durden, Tyler. "First Human Case of Flesh-Eating Screwworm Detected in Sanctuary State of Maryland." ZeroHedge, August 26, 2025.
2. Reuters. Cited in ZeroHedge article, August 26, 2025.
3. U.S. Department of Health and Human Services (HHS) statements, August 2025.
4. U.S. Department of Agriculture (USDA) announcements and reports, August 2025.
5. Centers for Disease Control and Prevention (CDC) confirmation, August 4, 2025.
6. Texas A&M University estimate on screwworm economic impact, referenced in ZeroHedge, August 2025.

What do you think about this article?

Name
Comment *
Image