United States Faces First Human Case of New World Screwworm as Maryland Traveler Brings Threat from Guatemala

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Published on
August 25, 2025

A person in Maryland has become the first known human case of the New World screwworm in the United States, a worrying development linked to travel from Guatemala. This parasite, which primarily affects livestock and wildlife, has now raised alarms for both health officials and agricultural sectors. The outbreak’s spread from Central America to the U.S. signals a potential escalation, especially with the current case being the first human infection reported in the country since the parasite began its northward march last year.

What Is the New World Screwworm?

The New World screwworm is a parasitic fly whose larvae cause serious harm to warm-blooded animals. Females lay their eggs in open wounds, where the eggs hatch into larvae that burrow into the flesh. This process is destructive, with the larvae feeding on living tissue, potentially killing the host if left untreated. The feeding method, which resembles a screw being driven into wood, is what gives these pests their name.

While screwworms mainly target livestock like cattle and other animals, humans are rare hosts, and infestations can be fatal if not treated early. Despite this, humans and animals alike can recover if medical intervention is prompt and effective.

The Maryland Case: Government Response

This alarming incident in Maryland has led to immediate action by health and agricultural authorities. The person infected was reported to have traveled from Guatemala, a country where New World screwworms have been present. Health officials from the CDC, as well as state officials in Maryland, were quick to confirm the case, triggering heightened surveillance and preventative measures.

Key agencies involved:

CDC: The Centers for Disease Control and Prevention, which oversees health risks associated with the screwworm.Maryland Health Officials: Local authorities working to track and manage the case.USDA: The U.S. Department of Agriculture, responsible for preventing the spread of the parasite to livestock.

Following the confirmation, the CDC and local health agencies swiftly engaged in efforts to prevent further spread, coordinating with the USDA and other agricultural groups. This response is crucial to containing the infection and protecting both public health and livestock.

How the New World Screwworm Affects Livestock and Agriculture

The New World screwworm is a significant threat to cattle and other livestock, as it can cause severe harm, including death, to affected animals. It’s also an economic threat to the agricultural industry in the U.S., particularly in states like Texas, which is a key hub for cattle production.

In fact, the USDA has estimated that an outbreak could cost Texas as much as $1.8 billion due to livestock deaths, lost productivity, and treatment costs. The current case in Maryland raises concerns about how easily the parasite could spread to other parts of the country, further harming the cattle industry.

Economic Impact: The New World screwworm could significantly disrupt the U.S. beef market, already struggling with tight cattle supplies.Livestock Industry at Risk: Cattle ranchers face potential losses, with additional costs to combat the spread of the parasite.

The USDA’s ongoing efforts to combat this pest have included plans to build a sterile fly facility in Texas to release millions of sterile flies. This approach has been used before during previous outbreaks to control screwworm populations. Despite these efforts, the current situation in Maryland highlights the need for continued vigilance.

The Role of the CDC and USDA in Managing the Situation

The CDC and USDA are working together to contain the situation, providing critical support to Maryland health officials and veterinarians. These agencies have implemented measures to prevent further cases, including monitoring livestock movements and conducting research into new ways to combat the New World screwworm.

CDC’s Role: The CDC was notified about the Maryland case and has been working closely with state officials to track and manage the outbreak.USDA’s Prevention Efforts: The USDA has put in place strategies to protect U.S. livestock from further screwworm infestations, including stricter border controls and the construction of a sterile fly facility to combat the pest.

The USDA’s plan includes a facility in Texas to combat the pest. This sterile fly facility, expected to take two to three years to fully operationalize, will play a crucial role in preventing future outbreaks.

Global Impact: Mexico’s Efforts to Contain the New World Screwworm

Mexico has been dealing with the spread of the New World screwworm since 2023, with cases reported across the country. In response, the Mexican government has been constructing a $51 million facility in the southern region to increase sterile fly production. These efforts aim to control the spread of the pest, which has already affected cattle in southern Mexico.

Given that Mexico is a major source of cattle imports to the U.S., the spread of the New World screwworm in Mexico poses a direct threat to U.S. agriculture. The U.S. typically imports over a million cattle from Mexico each year, and any disruptions in this trade could have serious economic repercussions.

Preventative Measures and Quarantine Protocols

To prevent further spread, the USDA has implemented quarantine protocols, halting the import of livestock from regions where New World screwworms have been reported. These measures are designed to limit the parasite’s reach into the U.S. while agricultural officials monitor the situation closely.

Some of the key actions taken include:

Closure of Trade Routes: The USDA has temporarily closed specific livestock trade routes to prevent the entry of infected animals.Increased Monitoring: Surveillance has been stepped up along the U.S.-Mexico border to ensure that livestock are not carrying the pest into the country.Conclusion: Ongoing Vigilance Needed to Prevent Further Spread

The confirmed human case of New World screwworm in Maryland has underscored the need for ongoing vigilance and coordinated efforts between local, state, and federal health and agricultural agencies. With the parasite continuing to spread through Mexico and Central America, maintaining tight controls at the U.S. border and tracking potential outbreaks is more crucial than ever. By continuing to monitor and respond swiftly, authorities can limit the impact on both public health and the agricultural industry, ensuring that the U.S. remains protected from this dangerous pest.

In the coming months, the successful implementation of sterile fly facilities and other control measures will be key in containing this parasitic threat and preventing its spread further into the U.S.