A mother brought her 5 year old son into his pediatrician with a “snake” that she found in his stool. Otherwise, the patient was completely asymptomatic.
Specimen sent for ID:
Ascaris is the most common Helminth affecting humans. It is also the largest of the roundworms (nematodes), growing up to 35 cm in length. There are several species of Ascaris however only A. lumbricoides affects humans.
Ascaris occurs in areas with poor sanitation, hygiene and solid waste practices. Worldwide it is most common in tropical and subtropical areas.
Transmission & Life Cycle
Ascaris is transmitted through the fecal-oral route, and is therefore most prevalent in areas with poor sanitation and waste practices. Transmission occurs when an uninfected person swallows a fertilized egg which was originally passed through the stool of an infected person.
The adult male and female forms live in the small intestine. The female passes up to 200,000 eggs per day. If there is also a male worm living in the small intestine, these eggs may then be fertilized. Both fertilized and unfertilized eggs are eventually passed in the stool.
Unfertilized eggs are not infective and do not cause disease if ingested. Fertilized eggs are only infective after approximately three weeks of maturation. The exact amount of time required before the fertilized egg becomes infective will depend on environmental conditions, such as temperature and humidity.
Once ingested, the fertilized egg travels to the small intestine, where it hatches and becomes a larva. The larval form invades the small intestinal mucosal wall and enters the bloodstream. Upon reaching the lung, the larva invades the capillary and alveolar walls and continues to grow within the alveoli. After about two weeks of maturation, the larva then migrates up through the airspaces and into the trachea, where it is eventually swallowed and transported back down into the small intestine. The fully mature larval forms are now adult worms and will continue to live in the small intestine for the rest of their lifespan (up to 1 to 2 years).
In most cases, Ascaris is diagnosed in the egg form on ova and parasite exam. The fertilized egg is round, 45-70 microns in diameter and has a thick, mammillated outer wall which stains brown with bile. The unfertilized egg is larger (90 microns), are has a more oval shape with a less regular mammillated contour. Patients may also pass adult worms in the stool or less commonly they may cough them up through the mouth. The adult worms have tapered ends with a three-lipped mouth (“tricuspid” mouth). The female is larger than the male (female: 20-35 cm, male: 15-30 cm).
Clinically, most people affected with Ascaris are asymptomatic. With a very high worm load however patients may begin to develop complications related to obstruction, including abdominal pain, constipation, appendicitis and obstructive cholangitis. In younger children infection with Ascaris may result in stunted growth. Of note, immune reaction to larva in the lung may result in an eosinophilic immunologic response known as Löffler’s pneumonitis.
Ascaris is treated with anthelminthic medication (albendazole, mebendazole or ivermectin). Therapy for Ascaris extremely effective and rids the patient of all adult, larval and egg forms.
-Javier De Luca-Johnson, MD is a 2nd year anatomic and clinical pathology resident at the University of Vermont Medical Center.
–Christi Wojewoda, MD, is certified by the American Board of Pathology in AP/CP and Medical Microbiology. She is currently the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.