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Hookworm Returns to the United States—Did It Ever Really Leave?

SEP 22, 2017 | KRISTI ROSA
Contrary to popular belief, hookworm—an intestinal parasite in humans consisting of larvae and adult worms that reside within the small intestine—still exists in the United States.

In fact, the Centers for Disease Control and Prevention (CDC) estimates that a staggering 570 to 740 million individuals around the world are infected with the parasite. Hookworm thrives in resource-limited countries, with severe poverty and poor sanitation. The worm flourishes in warm, moist climates typically found in regions such as South America, South Asia, and Southeast Asia.

“Hookworm was rampant in the United States more than 100 years ago. It thrived in the poor south, where many families could not afford proper outhouses and sewer systems were rare,” popular news source NPR reported in a recent article. However, according to the CDC, improvements in living conditions have succeeded in cutting down these infections. NPR reports that between the 1950s and 1980s, the worm was actually eradicated in the United States, although “the exact date isn’t clear.”

Unfortunately, findings from a new study published in The American Journal of Tropical Medicine and Hygiene, validates the presence of the worm in some areas of the United States, begging the question—did it ever really leave?

For their study site, the investigators chose an environment where hookworm would typically flourish—Lowndes County, Alabama—a place known for its “previous high hookworm burdens, degree of poverty, and use of open-sewage systems,” according to the study’s abstract. Lowndes County is one of the poorest counties in the country, according to NPR, one that cannot afford a septic system, leaving residents to create their own sewer line through the use of PVC piping, which goes from their toilets “and stretches off some 30 feet above ground until it reaches a small ditch.”

“This seems safe to [the residents],” lead investigator Rojelio Mejia, MD, a pediatrician and infectious disease specialist at Baylor College of Medicine, said in the article. “But Alabama is very hilly, and any drizzle of rain causes flooding, so whatever they delivered to the site spreads to the entire area, including their neighbors’ area.”

Investigators interviewed residents and collected stool, serum, and soil samples. They tested the samples for 9 different intestinal parasites that are commonly found in the tropics “using a multiparallel quantitative real-time polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assays.”

The investigators found that 42.4% of study participants reported being exposed to raw sewage in their home, which is not surprising because of their makeshift sewage systems. Furthermore, 19 out of 55 stool samples (34.5%) collected from the study participants came back positive for Necator americanus (a species of hookworm), 4 out of 55 (7.3%) tested positive for Strongyloides stercoralis (parasitic roundworm), and 1 out of 55 (1.8%) was positive for Entamoeba histolytica (an anaerobic parasitic amoebozoa). However, those with hookworm in their samples only had 1 or 2 eggs per gram of stool, a finding that greatly differs from countries endemic with the parasite.

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