Soil-Transmitted Helminths and Other Intestinal Roundworms

Infections with soil-transmitted helminths (STHs) affect the health of around 1.5 billion people around the world. Individuals of all ages may be infected with the common roundworm (Ascaris lumbricoides) , whipworm (Trichuris trichiura) , hookworm ( Ancylostoma duodenale and Necator americanus ), and Strongyloides stercoralis , although school-aged children living in resource-poor endemic areas are more likely to be infected with heavy worm burdens that contribute to significant malnutrition, delayed physical growth, cognitive impairment, serious illness, and even death. Light worm infections are usually asymptomatic; however, when STHs are diagnosed among returning travelers and immigrants from endemic areas, there is usually a strong personal desire to be free from worms whether symptomatic or asymptomatic.

Chronic infections with hookworm and whipworm can be associated with the development of iron-deficiency anemia owing to daily blood loss in the stools. Strongyloides can cause chronic infections in humans that persist for decades because of an alternate parasite autoinfective cycle that can bypass obligatory developmental stages in the soil, and such infections may be associated with skin rashes and hypereosinophilia, as well as fatal hyperinfection syndrome in immune-compromised hosts.

Another nematode (roundworm) included in this chapter is pinworm (Enterobius vermicularis) . Pinworm infections are a ubiquitous scourge among children and the households that they live in, usually causing perianal itching but occasionally associated with more serious pathology such as appendicitis.

There are many geographic areas where a high risk of STH transmission overlaps with high rates of HIV infections and acquired immunodeficiency syndrome (AIDS) among resident populations. Some studies have postulated that helminthic infections in persons co-infected with HIV may adversely affect HIV-1 progression, as measured by changes in CD4 count, viral load (measured by HIV-1 ribonucleic acid [RNA]), and/or clinical disease progression. Diagnosis of latent worm infections and appropriate treatment of HIV-1 co-infected persons and others with immunocompromised status are strongly recommended for those who live or have lived in high-risk geographic areas for STH transmission.

A 3-year-old boy was brought to clinic by his parents, who complained that during the past week, he had developed a peculiar skin rash that seemed to enlarge each day. He was last seen in clinic 9 weeks ago for a general physical exam upon their return from a year-long missionary assignment in Nigeria. At his previous visit, he was found to be in the 70th percentile for height and weight for his age, and had a normal physical exam. Screening blood tests and urinalysis were normal. The complete blood count with white cell differential showed no elevation of the eosinophil count. Stool ova and parasite (O&P) exam showed ova of Ascaris lumbricoides , hookworm, and Blastocystis hominis. As the boy had normal stools and no abdominal symptoms, he was prescribed Albendazole, 400 mg once as a single oral dose, as treatment against the Ascaris and hookworm; no treatment was prescribed for the Blastocystis . A posttreatment stool specimen submitted 1 month after treatment was negative for O&P. At this visit, the physical exam was normal except for the finding of a serpiginous erythematous track-like rash on the skin of his left buttock, starting at the anus and extending about 7 cm. The parents reported that he frequently scratched that area. A blood sample was taken to submit for Strongyloides serological testing. Ivermectin 200 mcg/kg per day po × 2 days was prescribed for the presumed diagnosis of Strongyloides stercoralis . The parents reported that 1 week after treatment, the itching was completely gone and the rash was fading away. Three weeks following the clinic visit, the Strongyloides serology test was reported back as positive. A repeat Strongyloides serology test will be done 6 months after treatment for follow-up.

COMMENT: Children with only light worm burdens of STHs often show no signs or symptoms of morbidity from their infection. The absence of finding S. stercoralis larvae in the submitted stool specimens is common in light infections because of irregular and scanty output; peripheral blood eosinophilia may or may not be present. While the single dose of albendazole initially prescribed was efficacious against Ascaris and hookworm, a longer course of albendazole therapy at a higher daily dose (Table 79.3) would be recommended for intestinal S. stercoralis infections; the drug ivermectin is considered primary therapy for the treatment of intestinal strongyloidiasis.