Widespread presence of threadworm suggests other forgotten diseases may be making a comeback

USC researchers have found evidence of threadworm (scientific name: Strongyloides stercoralis) in South Carolina in two different studies. Their research, which was published in The American Journal of Tropical Medicine and Hygiene, was led by  School of Medicine Columbia’s Matthew Haldeman and epidemiology professor Melissa Nolan and was conducted in USC’s Institute of Infectious Disease Translational Research.

“Threadworms are parasitic roundworms that affect up to one-third of the global population and can spread to animals such as dogs and cattle as well,” Nolan says. “They typically thrive in impoverished countries where residents have limited access to clean water and sanitation, so you wouldn’t expect to find cases of it in the United States.”

“Threadworm infections are particularly concerning for children because of their ability to cause chronic malnutrition and anemia, reduced cognitive functioning, and poor educational achievement,” adds Haldeman, who completed a USC Family Medicine-Global Health Fellowship Program, which included a Master of Public Health in Health Promotion, Education, and Behavior, in 2019. “Its spread is not only more likely to impact low-income populations, but these symptoms are also more likely to exacerbate the cycle of poverty that contributes to community-wide infections in the first place.”

With complementary backgrounds in global health and infectious diseases that disproportionately affect low-resource populations, Haldeman and Nolan teamed up to determine whether this highly contagious disease has been lurking undetected in the Palmetto state. Though thought to have been eradicated decades ago, their research shows that threadworms continue to flourish, particularly in the Appalachian Mountain Range and across the southeastern U.S.

In the absence of robust monitoring programs, like the one Nolan established in partnership with the SC Department of Public Health to monitor the presence and spread of tick-borne illnesses, the status of threadworm has remained largely unknown until recently. The last formal assessment of threadworm among South Carolina residents took place in 1972, and only a handful of monitoring efforts have taken place elsewhere in the country.

In the first part of the two-pronged study, the researchers examined the medical records from the state’s largest health system over a five-year period. The second part analyzed frozen serum samples previously obtained through Nolan’s ALL-IN project.

Based on this state-wide sample, USC researchers found five percent of study participants were  either recently or currently infected with threadworm. They were especially surprised to learn that nearly a third of the infections were believed to have been acquired locally, with 85 percent of impacted residents reporting no recent travel history.

“This research provides concrete evidence that serves as a contemporary reminder to public health and medical providers who serve the southern United States’ vulnerable populations that neglected infections are still occurring, and we have a long way to go to mitigate and eliminate these forgotten diseases,” Nolan says. “Future studies are needed to eliminate this chronic parasite that can exacerbate cognitive and physical disabilities and hinder one’s upward economic mobility.”

Co-authors include Henry Heidt (Research Associate, Nolan Lab) and Salome-Joelle Gass (Ph.D. Student, Health Services Policy and Management). This work was partially funded by the CDC (Grant no. OT21-2103) and the University of South Carolina’s Big Data Health Science Center in collaboration with the South Carolina Center for Rural and Primary Healthcare as part of the state’s rural health initiative.