Border Threat: Flesh-Eating Parasite on the Verge of Spreading

Decades after its elimination, the screwworm fly reemerges as an economic threat to the US.

A Maryland resident recently contracted the New World screwworm after visiting El Salvador. The invasive parasite burrowed into the individual’s flesh.

Although the patient has fully recuperated, health authorities in Maryland confirmed no further cases have been detected. This marks a significant occurrence as it’s the first human case reported in the US in over fifty years.

Initially, this appears to be an isolated incident linked to travel, posing minimal immediate risk. Yet, it serves as an emerging alert of a substantial threat approaching the US, particularly affecting its agricultural stability.

For around twenty years, a cooperative effort between the US and Panama maintained a barrier designed to keep screwworms at bay along the Panama-Colombia border. However, this barrier has weakened, and since 2023, the flies have surged through Central America and into Mexican territories.

A Looming Agricultural Hazard

Screwworm infestation progresses swiftly as the insects lay eggs in wounds. A single injury can draw multiple swarms, particularly impacting closely packed herds of cattle. Visible damage signifies advanced infestation stages and the distribution of flies. Over the past year, these outbreaks have cost Mexican cattle exports approximately $1.3 billion, per the Mexican National Agricultural Council.

These outbreaks can devastate livestock herds quickly. Given the high costs of cattle rearing and production, the American livestock sector dreads screwworms, arguably more than illnesses like mad cow disease. In Texas, an outbreak might cost the economy up to $1.8 billion annually.

Previously successful eradication efforts in the US are being revisited with significant financial commitments. This past May, $21 million was invested in renovating a Mexican facility to produce sterile flies aimed at controlling proliferation. Also, $8.5 million is allotted to establish a new plant in southern Texas. Yet, is relying on mid-20th-century methods adequate against such evolving risks?

Experts indicate that conditions have transformed over the past fifty years. Due to climate change, warmer environments extend potential habitats for screwworms. Expanding industrial livestock operations mean outbreaks could spread more rapidly through herds. Additionally, previous political decisions led to a reduction in skilled USDA personnel, impacting monitoring capabilities.

Secrets of the New World Screwworm

Originating from parts of South America and the Caribbean, the New World screwworm is a parasitic fly that resembles normal houseflies but possesses unique and menacing traits.

Attracted to warm-blooded animals, female screwworms deposit eggs in open wounds. They can lay up to 200 eggs at a time. Within 12-24 hours, larvae emerge, embedding themselves into tissue with painful consequences. Scientifically termed Cochliomyia hominivorax, or 'man-eater,' these flies earn their name by feeding on hosts while they're alive.

After sustenance for about a week, the larvae exit the wound and drop to the ground to pupate. They mature into adult screwworm flies and the cycle recommences.

The Brutal Impact

Unlike many parasites, screwworms devour only viable tissue. This behavior serves as an invitation for more flies, resulting in overwhelming infestations that can critically harm livestock. While humans experience significant pain from infestations, in animals, untreated infestations can lead to thousands of larvae feasting on a single host, often resulting in severe consequences such as collapse or death of the animal.

Historical Eradication Efforts

Once a major problem in the southern and western United States, screwworms used to inflict significant economic damages on American cattle farmers.

Back in the 1950s, scientists from the USDA devised a strategy capitalizing on the fly's own biology by introducing sterile mates into the environment, thereby disrupting reproduction. This method became known as the sterile insect technique (SIT).

SIT entails breeding large quantities of screwworms in controlled settings and sterilizing them through radiation exposure. These sterile insects are then released from planes over affected areas. As these flies couple, no offspring are produced, successively causing the population to diminish.

The initial eradication campaign in the American Southeast progressed through the 1950s and eventually broadened toward the Southwest. Collectively, the programs demanded a $42 million investment.

Current and Future Challenges

Despite previous success, 2023 witnessed vulnerabilities where new outbreaks were instigated by illegal cattle movement exacerbated by climatic shifts favoring screwworm proliferation. Presently, measures are underway to restore containment, with extensive production of sterile flies commencing in Mexico and upcoming manufacturing initiatives in Texas.

What Lies Ahead

Recent financial commitments focus on amplifying sterile screwworm output, targeting threatened locations in southern Mexico. Legislative moves, such as the STOP Screwworms Act, are being pursued, which would officially back these biosecurity initiatives.

This robust mobilization reflects how screwworms are prioritized distinctively compared to other agricultural threats, emphasizing their potential impact on the US's livestock sector.

For example, avian flu has resulted in mass losses within the poultry industry with substantial recovery packages, yet screwworms are perceived as a problem of national security magnitude.

There's significant economic pressure, as the cattle industry stands at $112 billion, and any substantial outbreak could incur billions in losses. Current plans focus on prevention, yet, FDA-approved treatments for humans and animals are still lacking, requiring accelerated evaluations of prospective technologies.

Moving forward may necessitate overcoming coordination challenges within the USDA, particularly given the recent staff reductions, to ensure successful implementation of proposed measures and safeguard the vital agricultural sector.