Page 117 - JSOM Summer 2018

An Ongoing Series

Ascariasis

Mark W. Burnett, MD

Introduction Diagnosis
Ascariasis is one of the most common infections worldwide, Diagnosis is usually made by the detection of ova (eggs) in
with an estimated one in seven humans (or 1 billion individ- fresh stool by light microscopy, an often time-consuming pro-
uals) infected with the parasitic worms. Although ascariasis cess that requires training. Adult worms also can be found in
is uncommon in the United States, except in those who have the stool, can be passed from the mouth during episodes of
traveled overseas, Ascaris infections are common in the de- vomiting, or can migrate out of the nares, especially if an un-
veloping world. This is especially true among children in ar- treated patient is undergoing general anesthesia. Quantitative
eas where personal hygiene has been compromised because polymerase chain reaction testing of the stool for egg DNA
of poverty and fecal contamination of the environment either has been used with success in research laboratories around the
intentionally, as in using human waste as fertilizer, or uninten- world, but no formalized test is approved for use.
tionally, as in improper waste disposal. Most infections are
asymptomatic in the healthy American adult, but chronically Treatment
infected children in the developing world can be malnourished
or suffer from intestinal obstructions with high worm burdens Albendazole at a dose of 400mg once or ivermectin at a dose
if untreated. of 150–200μg/kg orally once are usual treatments for non-
pregnant and nonlactating adults. Mebendazole is difficult to
Background and Clinical Presentation find in the United States but is used overseas. The US Food
and Drug Administration does not specifically approve the
Ascaris lumbricoides is a parasitic roundworm in the nema- use of these medications to treat Ascaris infections, but they
tode family that can infect humans; A. suum infects pigs and are used in the United States. The World Health Organization
humans. After being passed in the stool of an infected human recommends once-yearly treatment of children in national
or pig, the Ascaris eggs must be incubated in soil for several campaigns in areas where the prevalence of infections is be-
weeks before they become infectious. A single female worm tween 20% and 50% and twice-yearly treatment campaigns
can produce 200,000 eggs per day, which can remain viable in where the prevalence of infections is greater than 50% of
soil for years in a tropical climate. After a host ingests infec- children.
tious eggs from the environment, the larvae hatch in the small
intestine, penetrate the mucosal lining, and are transported via Vaccination
the blood of the portal system to the liver and the lungs. The
larvae then climb into the pharynx, where they are swallowed No vaccination currently exists for the prevention of Ascaris
and grow into adults in the small intestine. An adult worm can infections.
develop by 8 weeks after ingestion and, in the case of the adult
female, can pass eggs into the environment through stool for Importance in a Deployed Setting
the next 12–24 months. Most infections are without symp-
toms, but the larvae migrating through the lungs can cause a Although ascariasis seldom causes significant health concerns
pneumonitis (called Löffler syndrome). Heavy worm burdens in deployed forces, the psychological distress caused by a
can cause intestinal obstruction, and worms can migrate into worm passed in stool, vomited, or coughed up cannot be un-
the common bile duct or appendix. Intestinal obstruction is derestimated. Prevention while overseas is key and includes
most commonly seen in children, who have a smaller lumen eating foods from approved sources; avoiding high-risk foods
in their intestinal tract. Malnutrition can result from heavy (e.g., lettuce, sprouts), which are often grown in soil fertilized
worm burden in an at-risk child, especially where reinfection with human waste and washed off in contaminated water; and
rapidly follows treatment in an unclean environment. practicing proper hand hygiene after using the latrine and in

COL Burnett is currently chief of Pediatric Infectious Diseases at Tripler Army Medical Center, Honolulu, Hawaii, and is the Pediatric Subspe-
cialties Consultant to the US Army Surgeon General. He is board certified in Pediatrics and Pediatric Infectious Diseases. He has served overseas
in Korea, Germany, Kosovo, Iraq, Afghanistan and Kuwait, and as the Joint Special Operations Task Force—Philippines (JSOTF-P) Surgeon. He
is a graduate of the University of Wisconsin-Madison, and the Medical College of Wisconsin.

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