Francesca Tomasi received her B.A. from the University of Chicago and currently researches tuberculosis drug targets in search for novel antibiotics.
Ascaris lumbricoides, more simply referred to as Ascaris, is Earth’s most common parasitic roundworm. Four leading species of soil-transmitted helminths together account for 1.5 billion global infections, approximately 25% of the world’s population. Ascaris is responsible for about 820 million of these infections and for at least 60,000 deaths per year. Ascaris owes its success to physiological hardiness, sneakiness, and to poor human hygiene.
While A. lumbricoides can survive in many different environments, its preferred ecosystem is tropical – warm and wet, where it thrives in soil. Approximately 73 percent of people with ascariasis live in rural Asia, 12 percent in Africa, and 8 percent in South America. Certain subpopulations in these regions experience infection rates as high as 95 percent. Meanwhile, in the United States, the current prevalence of A. lumbricoides in stool samples is approximately two percent, with cases concentrated in poor rural areas.
Ascaris infects people of all ages but is most common in children, who tend to engage in high-risk behavior such as playing in soil and putting contaminated hands in their mouth. Once ingested, worms burrow into the small intestine and remain there for a period of 10 months to two years to mature before eventually being passed in stool. Adults can reach a length of 30 centimeters. A female worm produces around 200,000 eggs per day, which are shed through stool and can then be ingested by somebody else through contaminated soil or water.
Roundworms are diagnosed by looking at stool samples through a microscope and identifying eggs. While Ascaris infections are typically asymptomatic, individuals may experience some abdominal discomfort. In extreme cases, a heavy infection can physically block the intestine and cause significant morbidity and possibly even mortality. Obstruction tends to stunt growth in children. The good news is that anthelminthic medications exist to treat parasitic worm infections. These drugs, with names like albendazole and mecendazole, are administered for one to three days and effectively treat Ascaris infections.
Simply put, the global burden of ascariasis drastically overshadows the basic fact that Ascaris infections are easily prevented and treated. According to the CDC, so-called Mass Drug Administrations (MDAs) are conducted annually in high-risk regions. In these events, drug distributors go door to door and hand out anthelminthic drugs to treat any lurking cases of ascariasis and other neglected parasitic diseases. Since treatment does not lead to drug resistance and medications are inexpensive (and often donated), the World Health Organization recommends preemptive treatment of high-risk groups without requiring a diagnosis. The WHO specifically identifies preschool and school-age children, women of childbearing age, and pregnant women as having the highest risk of heavy (symptomatic) infections.
Just as with most infectious diseases, the best preventive methods are not chemotherapeutic. The best ways to prevent ascariasis are to avoid ingesting soil or unpurified water, as well as to wash hands frequently and fully clean or cook food. Furthermore, effective sewage systems prevent transmission of Ascaris and the hundreds of other pathogens that spread through fecal-oral contact.