Third-century baths and sanitary facilities at Vindolanda, a Roman stronghold near Hadrian’s Wall in England
Vindolanda Trust
Although the Romans were recognized for their sophisticated sanitation systems, those stationed in major forts in northern England likely endured numerous digestive illnesses caused by parasites.
The Vindolanda Fortress, situated close to Hadrian’s Wall and inhabited by Roman soldiers from the 1st to 4th century AD, was likely not suitable for individuals with sensitive stomachs, as excavations of waste pits at this location indicate.
Piers Mitchell and his team from the University of Cambridge collected and examined nearly 60 sediment samples from the communal toilets believed to have been utilized in the 3rd century.
Utilizing microscopy, they discovered the eggs of two intestinal parasites: roundworms and whipworms. Additionally, they identified a one-celled parasite called duodenal giardia through specific antibodies that bind exclusively to proteins found in this organism.
All three parasites can lead to gastrointestinal issues, which can be particularly severe for children, the elderly, and immunocompromised individuals.
“Even with our efforts to implement Roman conveniences like baths and toilets, we still faced diarrhea and intestinal parasitic diseases,” Mitchell remarked.
Structures such as toilets, baths, aqueducts, and fountains primarily served to enhance air quality and maintain visible cleanliness, he explains. “They lacked microscopes and therefore were unaware of many infections that plagued them.”
Whipworm eggs discovered in a sewer pipe in Vindolanda
Marissa Ledger
Excavations at another nearby fort, occupied in the 1st century AD and believed to have defensive ditches, also revealed roundworms and whipworms.
“The contents of the sewage drains consist of mixed fecal matter from various individuals utilizing the toilets, making it difficult to determine the infection rate among soldiers,” Mitchell states. “However, the presence of parasite eggs along the sewer drains implies that a considerable number of individuals using the facilities were likely infected.”
Roundworms and whipworms are also found throughout the Roman Empire; giardia, however, has only been identified in the Roman contexts in Turkey and Italy, according to Mitchell.
If asked whether he would like a glass of water during the time the fort was operational, he would certainly decline. “They might say, ‘How about a beer instead?'”
Exploring Hadrian’s Wall and Roman Innovations: England
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In September, Mexican officials confirmed an outbreak of the lethal flesh-eating parasite in Nuevo Leon, located less than 70 miles (113 kilometers) from the Texas border.
The outbreak was identified in an 8-month-old cow along the busy Monterrey to Laredo highway. Cocliomia hominivorax – the New World screwworm – has resurfaced for the first time in decades, threatening its eradication status achieved in the United States over fifty years ago.
This discovery raised concerns among U.S. ranchers and veterinarians who vividly recall the destruction this voracious insect once wreaked. The screwworm fly, a metallic blue-gray, appears relatively ordinary until its larvae begin to burrow into the living flesh of animals.
“The adults resemble the blowflies commonly found in my lab in North Carolina,” remarks Professor Max Scott, an entomologist at North Carolina State University who has dedicated his career to pest research. “The difference is that this blowfly is an obligate parasite. The female must lay her eggs in a living host.”
Within hours of being laid in a wound or natural opening, the eggs hatch into maggots that burrow deep into the tissue. After several days of feeding, the larvae drop to the ground and pupate, often leaving the host deformed or dead.
Each female can lay hundreds of eggs, and untreated infestations often attract other species of flies, exacerbating the host’s decline.
In livestock, screwworms can result in significant weight loss, skin damage, and even fatalities, representing a multibillion-dollar challenge for the livestock industry in South America.
A Terrible Past
The New World screwworm once plagued regions in the southern United States, Mexico, and the Caribbean. It wasn’t until the mid-20th century that an unexpected mix of genetics, radiation, and air transport helped regain control over the species.
Post-World War II, scientists at the United States Department of Agriculture (USDA) pioneered germ-free insect technology, a groundbreaking method for genetic control. The approach was both simple and radical—breed millions of screwworm flies in captivity, sterilize them using gamma rays, and release them into the wild.
Females mate only once, so even if they pair with a sterile male, they won’t produce offspring, leading to a population collapse.
In the 1950s, experiments on Curaçao confirmed the method’s effectiveness. By the early 1960s, screwworms had been eradicated from Florida. The initiative spread west and south, ultimately eliminating the fly from the continental United States, Mexico, and much of Central America by the early 2000s.
The eradication campaign was costly, reportedly exceeding $750 million. However, it saved the livestock industry billions in losses annually and allowed U.S. cattle production to thrive in the following years.
A small production facility in Panama, jointly managed by the U.S. and Panamanian governments, maintained permanent barriers, releasing 100 million sterile flies weekly along the Panama-Colombia border and regularly developing new strains for longevity.
This system functioned effectively for two decades until it faltered. By 2023, infection cases began to re-emerge in Panama. Within two years, the parasite spread to Costa Rica, Nicaragua, and Honduras, now reaching northern Mexico.
New World screwworm larvae feed on infected animal wounds for about seven days, then fall to the ground, burrow into the soil, and pupate. – Credit: COPEG
What Went Wrong?
The specific reasons behind the barrier’s collapse remain unclear, but Scott noted “warning signs indicating trouble along the border.”
Farmers failing to adhere to protocols when transporting livestock may have further facilitated the spread of infection, explaining the surge in cases beyond the natural movement of fly populations.
Scott pointed out that the Panama facility is currently overburdened, producing around 110 million sterile flies weekly. In contrast, during the initial eradication efforts in Mexico, local facilities generated between 500 million and 700 million units weekly. “We needed that volume,” he noted.
This shortfall means an insufficient supply of sterile flies to manage the ongoing outbreak.
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The Enemy at the Gate
As of now, there is no evidence that the screwworms have crossed into the U.S. The USDA has deployed approximately 8,000 traps in Texas, Arizona, and New Mexico but has not detected any flies. Nevertheless, vigilance is high.
“The risks are substantial,” Scott cautions. “The best chance to curb the outbreak was further south, near the Isthmus of Tehuantepec. Reports of cases further north complicate containment given the current production capacities.”
In response, the U.S. government initiated a “five-pillar plan,” which includes constructing two new fly dispersal facilities in Texas. One facility at Moore Air Force Base can spray 100 million sterile flies weekly, while plans for a larger production plant in southern Texas aim to triple that capacity.
The USDA is also investing $100 million into innovative pest control technologies, exploring options from electron beam and X-ray sterilization to genetically modified flies.
A significant resurgence of screwworms could be catastrophic for U.S. livestock producers. An outbreak may incur billions in animal losses, quarantines, and trade restrictions. When the parasite re-emerged in Florida in 2016 from Caribbean-imported deer, it infected 145 animals, taking nearly a year to eradicate.
Human infections are rare but can be severe. The parasite’s scientific name, Cocliomia hominivorax, translates to “man-eating fly.” Most cases affect travelers to infested regions, leading to infections from wounds and nasal passages.
“This is not a major public health issue,” Scott explained. “However, caution is advised when visiting affected areas.”
The bulges on the larva’s body are the origin of the name “screw maggot.” – Credit: USDA Agricultural Research Service
Modern Genetic Upgrades
Scott believes that the old sterile fly method remains viable, especially when enhanced by new biotechnology. His lab at North Carolina State University has spent years developing genetically engineered screwworm strains that produce only males, significantly increasing efficiency.
Traditional sterile insect techniques require releasing both males and females, resulting in many males mating with sterile females.
This means that very high doses of radiation are needed to fully sterilize females, Scott noted. In contrast, his team’s method yields only males. They can then focus on sterilizing these males specifically, allowing researchers to maintain a higher quantity of healthier flies unlikely to reproduce.
These male-only stocks were field-tested in Panama in 2018 but were not deployed because existing methods were deemed sufficient. As the parasite moves northward, regulatory approval for genetically modified screwworms might become essential.
Moreover, researchers are investigating “gene drive systems” utilizing CRISPR technology to bias genetics, ensuring that most offspring carry infertile or male-only genes. In theory, this could drastically reduce the number of flies needed for suppression.
“We hope funding will be available to develop more effective technologies,” Scott stated. “The goal is to reduce releases from 100 million sterile flies to potentially just 10 million. This would make genetic control far more feasible.”
For the time being, strategies remain focused on aerial dispersal, targeted capture, and cross-border collaboration. Yet, scientists are increasingly concerned about the screwworm’s capability to migrate northward faster than anticipated.
“Given the current fly population, we sincerely hope to prevent them from entering the United States,” Scott warned. “But uncertainties remain.”
At present, the border remains intact. With each new case emerging towards the north, the focus shifts from whether the screwworms will invade the U.S. to whether they will be prepared upon their arrival.
Could scientists use parasites in your brain to treat diseases? The concept of utilizing parasites as a medical tool may sound unconventional, but it offers hope for conditions like Parkinson’s and Alzheimer’s. Researchers believe that if parasites can transport drugs directly to the brain, it could aid in treating these ailments.
An international team of scientists is doing just that. They are utilizing single-cell parasites called Toxoplasma gondii, which causes the infection toxoplasmosis. These parasites naturally travel from the human intestine to the central nervous system and provide proteins to host cells. In their experiment, bioengineers manipulated the internal system of T. gondii cells to produce and release proteins outside the cell, creating a secretion system.
The team explained that delivering medications to the brain is challenging due to the blood-brain barriers that safeguard the brain from harmful substances. T. gondii has evolved the ability to overcome these barriers, which could be beneficial in this process. Initially, they tested whether T. gondii can cross the blood-brain barrier in mice and then in human brain cells, specifically neurons, before moving on to testing on intact mouse brains to potentially apply the findings to humans.
Their drug delivery system mediated by T. gondii consists of proteins created from at least two regions of different genes that are combined and translated into a single unit, known as a protein fusion. They incorporated a therapeutic drug with a T. gondii protein called takihorin to transport medicine to the brain.
Initially, scientists faced challenges in determining the appropriate dilution factor for the drug compound. They had to find a balance between allowing the proteins to pass through the blood-brain barrier while ensuring they were still therapeutically effective. Through trial and error, they found the correct dilution factor and successfully administered the treatment to the targeted brain area.
The next step involved delivering therapeutic proteins to brain cells through T. gondii. Researchers used lab-grown mouse brain cells and specific proteins that regulate the movement of molecules across the cell membrane, known as vesicle transport protein. They demonstrated that the engineered T. gondii successfully transported healing proteins to the brain cells of lab-grown mice.
The researchers then tested the treatment process on human brain cells cultivated outside of the body. They confirmed that the therapeutic proteins delivered by T. gondii could bind to the DNA of human brain cells. This binding altered gene expression in the laboratory-grown brain cells.
Finally, engineers demonstrated the success of this therapy on whole mouse brains. By ensuring that the therapeutic proteins could pass the blood-brain barrier in live mice, they then evaluated the brains post-euthanasia. Utilizing 3D imaging, they illuminated specific neural pathways and markers in the mouse brain, confirming that the engineered proteins effectively delivered therapeutic proteins to the brain.
The researchers concluded that their findings show progress in drug delivery via engineered parasites but emphasized the need for further research to determine the potential advantages and drawbacks of this method. With the success of this study, they proposed that utilizing engineered parasites for drug delivery could offer new treatment options for brain-related diseases.
Duodenal hookworms (Ancylostoma duodenale) cause one of the most common intestinal parasitic infections worldwide.
Katerina Conn/Shutterstock
People with intestinal parasitic infections, quarter This has been suggested by experiments in mice infected with the parasite, which had significantly weaker immunity after receiving a COVID-19 vaccination compared to mice not infected with the parasite.
Previous studies have shown that people with intestinal parasitic infections have a weakened immune response to vaccines for diseases such as tuberculosis and measles because the parasites suppress the processes that vaccines trigger to confer immunity, such as activating pathogen-killing cells. Intestinal parasitic infections are most common in tropical and subtropical regions, where they often occur because of limited access to clean water and sanitation.
Scientists have not tested whether these pathogens reduce the effectiveness of COVID-19 vaccines. Michael Diamond Researchers at Washington University in St. Louis, Missouri, vaccinated 16 mice with a COVID-19 mRNA vaccine, half of which had been infected 12 days earlier with an intestinal parasite that lives only in rodents. They gave each mouse a booster shot three weeks after the first vaccination.
About two weeks after the booster shot, the researchers analyzed the animals' spleens to measure concentrations of CD8+ T cells, specialized white blood cells that are important for eliminating other cells infected with the SARS-CoV-2 virus. They found that the spleens of mice infected with the intestinal parasite had about half the number of cells as mice without the parasite, suggesting a weakened immune response to the vaccine.
The researchers repeated the vaccination process in another group of 20 mice, half of which were infected with the intestinal parasite, exposing them to the highly infectious Omicron variant of the SARS-CoV-2 virus. After five days, the lungs of vaccinated rodents infected with the intestinal parasite had, on average, about 20% more virus than uninfected ones.
These findings suggest that intestinal parasites may reduce the effectiveness of COVID-19 vaccines in people, but different types of intestinal parasites are known to affect immunity differently, the researchers say. Keke Fairfax The University of Utah researchers said it's unclear whether the parasite's infection in humans would have the same effect on vaccinating against COVID-19 as it did in mice, and the situation is further complicated by the fact that humans tend to harbor multiple types of intestinal parasites at the same time, they said.
Still, understanding how to alter the immune response to vaccination is important given the prevalence of parasitic infections, and these findings suggest that researchers may need to further evaluate the vaccine's effectiveness in parts of the world where a high proportion of the population is infected with intestinal parasites, Fairfax says.
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