Introduction - Putting Sensational Headlines in Perspective

Recent media reports, with headlines featuring phrases like "horrific flesh-eating parasite," have understandably caused public alarm.¹ The story of the first human case of the New World screwworm detected in the United States in years is a serious one, but the nature of that seriousness has been widely misinterpreted. The language used in many articles evokes images of an imminent and widespread public health crisis, a narrative that is not supported by the facts. The reality of the situation is far less frightening for the general public and far more focused on a different, though equally significant, national challenge: protecting our agricultural economy and animal welfare.

This report will separate the sensationalism from the science. The core message from the U.S. Department of Health and Human Services (HHS) and the Centers for Disease Control and Prevention (CDC) has been consistent and clear: the risk to public health in the United States from this case is "very low".² This is not a story about a new plague spreading through our communities. Instead, it is a story about a single, travel-related medical case that serves as a critical alert for a major agricultural threat we have successfully defeated before.

The intense government response, which may seem to contradict the message of low public risk, is not evidence of a hidden danger to humans. Rather, it is a rational and proactive defense against a known economic and ecological threat to livestock and wildlife. The recent headlines highlight a common pattern in how we perceive risk; a visceral, personal threat, no matter how rare, often captures our attention more than a larger, more abstract economic one. This report aims to re-contextualize the narrative, moving it from one of fear to one of understanding. By examining the specifics of the case, the biology of the organism, the history of its eradication, and the modern defense strategy, a clearer picture emerges—one that should inspire confidence in our public and animal health systems, not anxiety.

The Maryland Case - A Traveler's Tale, Not a Local Threat

To understand why public health officials are not alarmed about a widespread outbreak in humans, it is essential to examine the precise details of the recent case. On August 4, 2025, the CDC confirmed that a resident of Maryland was diagnosed with myiasis, the medical term for an infestation of fly larvae, caused by the New World screwworm, Cochliomyia hominivorax.¹ This confirmation was the result of a coordinated investigation between the Maryland Department of Health and the CDC.³

The single most important fact in this case is its origin. The infection was "travel-associated".² The patient had recently returned to the United States from a trip to El Salvador, a country where the New World screwworm is known to exist.¹ This means the individual was not infected in their Maryland home or community; the parasite was acquired abroad and brought into the country. Early reports from some industry sources and media outlets created minor confusion by suggesting the travel originated in Guatemala, but official statements from HHS later clarified the location as El Salvador.³ This detail, while important for epidemiological tracking, does not change the fundamental takeaway: this was an imported case.

Crucially, the situation was contained. The patient received medical treatment, and authorities have reported no subsequent animal or human cases in the United States stemming from this event.² The absence of any animal cases is particularly significant, as livestock are the primary hosts for this parasite. It indicates that this was an isolated incident, not the beginning of an established infestation.

Furthermore, while this case is the first to be linked to the recent outbreak advancing through Central America, it is not the first time a U.S. traveler has returned with this specific parasite. A review of CDC records shows other isolated, travel-associated cases in recent years. In 2014, a woman was infected after a trip to the Dominican Republic. In 2023, a man with a fresh surgical wound became infested while traveling in Argentina and Brazil. And in 2024, another individual returning from the Dominican Republic required surgical removal of over 100 larvae from their nose. Other past cases have been linked to travel in Peru and Colombia.⁷

Placing the Maryland case within this historical context is vital. It is not an unprecedented invasion but a rare and unfortunate, yet known, risk associated with travel to specific regions of the world where the parasite is endemic. The case serves as a biological "sentinel," a tangible data point confirming that the northward spread of the screwworm in Central America has now progressed to a point where it can intersect with modern human travel patterns. It transforms a distant agricultural problem into a present, albeit very limited, public health reality, justifying the swift and coordinated response from health officials who view it as a data point in a much larger epidemiological puzzle.³

Understanding the Organism: The Science Behind the "Screwworm"

The term "flesh-eating" is scientifically imprecise but emotionally powerful. To move past the fear it generates, it is necessary to understand the biology of the organism at the center of this story: the New World screwworm fly, Cochliomyia hominivorax. The adult fly itself is unremarkable, roughly the size of a common housefly, distinguished by a metallic blue-green body, orange eyes, and three dark stripes along its back.⁸ The real threat lies not with the adult fly, but with its larval stage, commonly known as a maggot.

The life cycle of C. hominivorax is the key to understanding its destructive potential. A female fly, which uniquely mates only once in her life, is attracted by the scent of a wound on a warm-blooded animal—or, in rare cases, a human.⁹ This can be a major surgical wound, a cut, a scratch, or even something as small as a tick bite.¹⁰ She lays a mass of 200 to 300 eggs on the edge of this living tissue. Within just 12 to 24 hours, these eggs hatch into larvae.⁹

This is where the term "screwworm" originates. The larvae, equipped with sharp mouth hooks and encircling bands of spines, burrow headfirst into the healthy, living flesh of their host. Their feeding behavior, which involves twisting and driving deeper into the tissue, resembles a screw boring into wood.⁵ For the next five to seven days, they feed voraciously, destroying tissue and enlarging the wound, which can attract more female flies to lay more eggs.¹¹ Once mature, the larvae drop from the host to the ground, burrow into the soil to pupate, and later emerge as adult flies to repeat the cycle.¹³

The scientific term for this type of infestation is myiasis, which simply means the parasitic invasion of a live vertebrate by fly larvae.¹⁴ What makes the New World screwworm so dangerous, and what gives rise to the "flesh-eating" label, is that it is an

obligate parasite. This means its larvae must feed on the living tissue of a host to survive.⁹ This is the critical distinction that separates it from the thousands of other fly species in our environment. The common maggots we might see on decaying matter are typically saprophytes, meaning they feed on dead and rotting organic material.¹⁶ They play a crucial role as decomposers in the ecosystem and pose no threat to healthy, living animals. In fact, some species have been used in medicine for "maggot debridement therapy" to clean necrotic tissue from wounds precisely because they do not harm healthy flesh. The New World screwworm is the opposite; it requires living tissue, making it a true parasite and a serious threat to any warm-blooded creature it infests.

To clarify this crucial difference, the following table provides a direct comparison between the New World screwworm and the common maggots found throughout the United States.

Table 1: A Tale of Two Maggots

This distinction is the foundation for a rational understanding of the current situation. The threat is not from a common insect suddenly turning dangerous; it is from a specific, non-native parasite that has been effectively eliminated from our country for decades.

A Public Health Triumph: How America Defeated the Screwworm

The current concern about the New World screwworm is not a confrontation with a new or unknown enemy. On the contrary, the United States has a long and remarkably successful history with this parasite—a history of scientific ingenuity, large-scale logistical mobilization, and ultimately, total victory. Understanding this backstory is essential for building confidence in our ability to manage the current threat.

Before 1966, the New World screwworm was a constant and devastating feature of American agriculture and wildlife management. The parasite was endemic in the southern United States, overwintering in the warm climates of Florida, Texas, and southern California and Arizona.¹⁹ Each spring and summer, the fly population would expand, migrating northward and wreaking havoc on livestock and deer populations. The economic and animal welfare costs were immense. Ranchers were forced to schedule their operations around the fly's life cycle, timing branding, dehorning, and calving to occur during the coldest winter months when the flies were dormant or absent.¹⁹

The path to eradication began with a critical scientific discovery. In 1933, entomologists Emory C. Cushing and Walter S. Patton determined that the New World screwworm was a distinct species, Cochliomyia hominivorax, and not simply a variant of the common and far less harmful blowflies that feed on carrion.²⁰ This realization opened the door for targeted research. A major breakthrough came when USDA scientist Raymond C. Bushland developed an artificial medium of ground meat and blood that allowed for the mass-rearing of screwworm larvae in a laboratory, freeing researchers from the costly and inhumane practice of using live animals for experiments.²⁰

The most brilliant insight, however, came from another USDA entomologist, Edward F. Knipling. He observed a key vulnerability in the fly's biology: the female mates only once in her lifetime.⁹ From this fact, Knipling developed the theory of

autocide, or "self-destruction." He theorized that if a massive number of sterile male flies could be released into the wild, they would overwhelm the native fertile males. The wild females would mate with these sterile males, lay unfertilized eggs that would never hatch, and thereby fail to reproduce. The population would collapse under its own sterile biology.²⁰

This elegant theory became the basis for the Sterile Insect Technique (SIT). The process is a marvel of applied biology:

1. Millions of screwworm flies are mass-reared in a laboratory setting.²¹

2. In their pupal stage, they are sterilized using a precise dose of radiation (gamma or x-rays), which renders the males unable to produce viable sperm but does not otherwise harm their ability to fly, compete, and mate.²³

3. These sterile flies are then systematically released from aircraft over infested areas in numbers sufficient to outcompete the wild male population.⁵

4. Because the wild females mate only once, a single encounter with a sterile male is enough to end her reproductive life.⁸

5. With each generation, the ratio of sterile to fertile matings increases, and the wild population plummets until it is completely eliminated.⁸

After a successful pilot program on the island of Curaçao in the mid-1950s, the full-scale program was launched in the United States.¹⁹ Florida was declared free of the parasite in 1959. The effort then shifted to the Southwest, a much larger and more complex challenge. By 1966, through a massive, coordinated effort involving federal and state governments and livestock producer associations, the United States was officially declared free of endemic New World screwworm.⁷ The effort didn't stop there; the U.S. and Mexico collaborated to push a permanent "barrier zone" of sterile fly releases progressively southward, eventually eradicating the pest from all of Mexico and Central America down to a permanent barrier maintained between Panama and Colombia.²¹ This history is not just a pest control story; it is a foundational narrative of American scientific and logistical achievement. It frames the current situation not as a new crisis, but as a challenge for which we possess a proven, gold-standard solution.

The Real Threat: Protecting a Nation's Livestock, Wildlife, and Pets

If the risk to the general human population is very low, why is the U.S. government launching such a massive and expensive response? The answer lies in the devastating impact the New World screwworm has on animals, and the subsequent threat to the nation's economy and food supply. The true story of the screwworm is one of agricultural economics and animal welfare.

The financial stakes are staggering. The USDA estimates that the original eradication program saves the U.S. livestock industry approximately $900 million every year in prevented losses.¹² A recent economic analysis projected that if the screwworm were to become re-established in Texas alone, the economic damage could reach $1.8 to $1.9 billion, a figure that does not even account for recent record-high beef prices.² This is why officials refer to the pest as a threat to national security; it has the potential to severely disrupt a critical sector of the food supply chain.⁴

The economic cost is a direct result of the parasite's brutal efficiency. An infestation can kill a fully grown cow or other large animal in as little as 10 days if left untreated.⁵ The larvae's feeding causes intense pain and stress, leading to weight loss, a dramatic decrease in milk production in dairy cattle, and damage to hides that makes them worthless.²⁵ The wounds themselves are horrific, often becoming infected with secondary bacteria and emitting a foul odor of decay that attracts even more screwworm flies.⁸

This threat extends beyond the ranch fence. The New World screwworm is an indiscriminate parasite of all warm-blooded animals. This includes wildlife populations, which are impossible to monitor and treat on an individual basis. A stark reminder of this vulnerability came in 2016, when a small, localized outbreak occurred in the Florida Keys. The parasite was not found in livestock but in the endangered Key deer population, causing a significant number of painful deaths before an emergency SIT campaign successfully re-eradicated the pest in 2017.¹²

Domestic pets are also at risk. Dogs, cats, and other companion animals are just as susceptible to infestation as cattle.⁸ Any pet with an open wound, from a surgical incision to a simple scratch, could become a target for the female fly in an infested area. The resulting infestation can be severe and even fatal if not promptly treated by a veterinarian.²⁸ In recognition of this, the USDA has implemented strict rules for animals entering the country from regions where screwworm is present. For example, dogs must be inspected by a veterinarian and certified screwworm-free within five days prior to entering the United States.²⁸ This multi-species vulnerability illustrates the broader ecological and societal threat. The problem is not just a "cow problem" or a "human problem"; it is a systemic issue where the health of animals—whether livestock, wildlife, or pets—is directly linked to the economic stability and security of the nation.

The Modern Defense: A Proactive and Multi-Layered Strategy

The U.S. government's response to the northward advance of the New World screwworm is not a panicked reaction to the single human case in Maryland. It is a calculated, proactive, and multi-billion-dollar defense strategy based on the precautionary principle: the potential for catastrophic loss is so high that a massive, preemptive investment is not only rational but essential. The response is scaled to the potential risk to the agricultural sector, not the current reality of zero animal cases in the country.

In recent months, the USDA has unveiled a comprehensive five-part plan to defend the U.S. border and prepare for any potential incursions.⁵ This strategy is a textbook example of a modern, integrated pest management system.

First and foremost is the revitalization of our primary weapon: the Sterile Insect Technique. The government has announced plans to construct a new, state-of-the-art sterile fly production facility at Moore Air Force Base near Edinburg, Texas. This facility, estimated to cost $750 million, will be capable of producing up to 300 million sterile flies per week.⁷ Its strategic location near the U.S.-Mexico border will allow for rapid deployment. This represents a monumental commitment to bringing this critical defense capability back onto domestic soil, ensuring a reliable supply of sterile flies to protect the border and respond to any outbreaks.⁴

Second, the plan calls for enhanced border surveillance. This is not just a technological effort but a boots-on-the-ground operation. The USDA is hiring more mounted patrol officers, known colloquially as "Tick Riders," who will patrol remote border areas on horseback to inspect livestock and wildlife for signs of infestation. They will be supplemented by vehicle patrols and, in a novel addition, specially trained detector dogs capable of sniffing out screwworm infestations in animals at ports of entry.⁵

Third, the strategy relies on robust international cooperation. The U.S. is working closely with its counterparts in Mexico (SENASICA) to help contain the pest south of the border through enhanced surveillance and case reporting.²⁴ This is in addition to the long-standing program, co-managed with Panama, that maintains the permanent sterile fly barrier at the Darién Gap to prevent re-infestation from South America.⁶ This demonstrates a strategic, hemispheric approach to the problem.

Fourth, the government is streamlining its regulatory processes to ensure veterinarians have the tools they need. In August 2025, HHS issued a declaration that allows the Food and Drug Administration (FDA) to grant Emergency Use Authorizations (EUAs) for animal drugs that can treat or prevent screwworm.²⁹ Currently, no drugs are specifically approved for this use in the U.S. This action cuts through regulatory red tape, allowing for the rapid approval of effective treatments that may already be in use in other countries or approved for other purposes.⁴

Finally, the plan is forward-looking, investing in the next generation of control methods. The USDA has pledged up to $100 million to fund research and development into innovative technologies that could augment or eventually replace SIT. This includes searching for new, more effective traps and lures, developing potential therapeutic drugs that could be stockpiled, and exploring novel production techniques for sterile insects.²⁴ This comprehensive, multi-layered defense demonstrates that authorities are not merely reacting to events but are actively managing a known threat with a proven historical strategy and a clear vision for the future.

A Traveler's Guide to Prevention and Treatment

While the national response to the New World screwworm is a complex, industrial-scale operation, protecting oneself on an individual level is remarkably straightforward. The simplicity of the prevention and treatment measures for humans stands in stark contrast to the complexity of the agricultural control measures, reinforcing the central theme that the human health aspect of this issue is manageable with basic awareness and personal care.

The risk of contracting New World screwworm myiasis is confined to a very specific set of circumstances. According to the CDC, individuals at higher risk are those who travel to endemic areas—primarily parts of Central and South America and the Caribbean—and who meet additional criteria. These risk factors include having an open wound (from a cut, scratch, insect bite, or recent surgery), spending significant time around livestock in rural areas, and sleeping outdoors without protection.³ For the vast majority of people living in the United States who are not traveling to these specific regions, the risk is effectively zero.

For those who do travel to at-risk areas, the symptoms of an infestation are distinct. The primary symptom is a painful skin lesion or sore that does not heal and may worsen over time.¹⁰ Patients often report a disturbing sensation of movement within the wound.¹⁰ Upon inspection, the cream-colored larvae (maggots) may be visible deep within the wound, and the site may produce a foul-smelling discharge. Secondary bacterial infections can sometimes occur, leading to fever or chills.¹⁰

Diagnosis is typically made by a healthcare provider through visual identification of the larvae in the wound.¹⁰ The treatment is direct and effective: the physical removal of all larvae from the tissue. Because the larvae anchor themselves with their spines, this sometimes requires a minor surgical procedure to open the wound and ensure every larva is extracted.¹ Once the larvae are removed, the wound is thoroughly cleaned and treated with antibiotics if a secondary bacterial infection is present.³¹ While the anti-parasitic drug ivermectin has been used off-label in some cases to help paralyze the larvae and facilitate removal, the cornerstone of treatment remains the complete physical extraction of the parasites.³¹

Given the effectiveness of treatment, prevention remains the best and easiest course of action for travelers. The CDC provides clear, simple guidelines ¹⁰:

• Wound Care is Paramount: Keep any and all open wounds, no matter how small, meticulously clean and covered with a secure bandage. This is the single most effective preventative measure, as it denies the female fly a place to lay her eggs.

• Use Insect Repellent: Apply an EPA-registered insect repellent to exposed skin.

• Wear Protective Clothing: Wear loose-fitting, long-sleeved shirts and pants to minimize exposed skin.

• Protect Sleeping Areas: Sleep indoors or in rooms with intact screens on windows and doors. If sleeping in less secure accommodations, use a bed net.

By following these basic personal hygiene and travel-preparedness steps, individuals can effectively eliminate their personal risk, allowing them to view the broader New World screwworm issue through the proper lens: as a manageable challenge for our agricultural and public health systems, not a cause for personal fear.

Conclusion - Stay Informed, Not Alarmed

The emergence of a single, travel-associated case of New World screwworm in Maryland has been amplified by sensational media coverage, creating a narrative of fear that is disconnected from the facts. A thorough review of the scientific, historical, and public policy context reveals a much different, and far more reassuring, story.

The key takeaways are clear and consistent across all official sources. The Maryland case was an isolated incident in an individual who had traveled abroad; it was quickly identified, treated, and contained, with no evidence of further spread.¹ The risk to the American public remains extremely low.² The parasite at the center of this story,

Cochliomyia hominivorax, is a well-understood organism whose "flesh-eating" behavior is a specific biological trait—an obligate parasite's need to feed on living tissue—that distinguishes it from common flies.⁹

The robust, multi-billion-dollar government response is not a sign of a hidden public health crisis. It is a prudent and proactive defense of the nation's multi-billion-dollar livestock industry, which is the parasite's primary and most vulnerable target.²³ This is a foe we have faced and decisively defeated before. The United States possesses a proven, scientifically elegant weapon in the Sterile Insect Technique, and the current strategy involves a massive investment to ensure this tool, along with a host of other surveillance and regulatory measures, is ready to protect our borders.⁸

In an age of rapid information flow, the New World screwworm story serves as a powerful case study in media literacy. It underscores the importance of looking beyond alarming headlines to seek out primary, authoritative sources like the CDC and USDA. By doing so, we can replace anxiety with knowledge and appreciate this situation for what it truly is: not a cause for public panic, but a testament to the vigilance and capability of the nation's interconnected public health and animal health defense systems.