Vol

DEPARTMENT OF PATHOLOGY
The Johns Hopkins Medical Institutions

Vol. 20, No. 33
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Tuesday, August 14, 2001

A. Provided by Leslie Edwards Reger, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.

6 outbreaks reported during MMWR week 31 (July 29 - August 4, 2001):
1 outbreak of gastroenteritis reported from households at a vacation area (Garrett Co.)
1 outbreak of conjunctivitis at an institution (Wicomico Co.)
1 outbreak of scombroid poisoning, believed to be related to tuna consumption, at a food-service facility (Allegany Co.)
1 investigation of a food-service worker with hepatitis A (Howard Co.)
1 outbreak of acute febrile respiratory disease at a nursing home (Carroll Co.)

B. The Johns Hopkins Hospital. Information provided by Robert W. Allan, M.D., Department of Pathology and Laboratory Medicine.

Case Report: The patient is a seven and one-half year old child who presented to clinic for a well child examination after recently emigrating from Somalia where his family had lived in a refugee camp. The patient reported to his father that he had seen small white worms in his stools. Otherwise, he denies fever, chills, cough, hemoptysis, shortness of breath, headache, skin rash, diarrhea or change in bowel habits, blood per rectum or abdominal pain. There were no reports of worms in the stools of his siblings. His appetite is good and he has not lost weight. He has no previous medical history. Physical examination is unremarkable. A stool ova and parasite exam was sent which revealed moderate Hymenolepis nana eggs and few to moderate Endolimax nana and Blastocystis homini. Hymenolepis nana (the dwarf tapeworm) Organism: Hymenolepiasis is caused by two different tapeworm (cestode) species, Hymenolepis nana and Hymenolepis diminuta. H. diminuta (the rat tapeworm) is infrequently seen in humans. Humans are the accidental host. The adult worm of H.diminuta measures from 20-60cm. H. nana is most commonly seen in children and is one of the most common tapeworm infections worldwide. It is also the only cestode that parasitizes humans without requiring an intermediate host. The adult worm of H. nana is small, measuring no longer than 4 to 5 cm. Often they are missed on gross examination of the stool as they simulate threads of mucus. The adult worm has indistinct, broader than long proglottids and a tiny scolex with 4 suckers and 20-30 hooklets (nature’s VelcroÒ ). The oval shaped egg form of H. nana measures 40 x 60 micrometers. The shell consists of two distinct membranes, an outer membrane with a smooth surface and an inner membrane with two opposite poles from which 4-8 filaments spread between the membranes. Inside the inner membrane are 3 pairs of hooklets (hexacanth ovum).

Life Cycle: The adult H. nana worms reside in the ileum where they produce proglottids that release eggs that are carried in the stool. The eggs in the stool cannot survive outside the body for more than 10 days. The eggs are ingested from food or water that is contaminated with feces. Once in the intestines the external membrane ruptures and the hexacanth ovum is released where it invades an intestinal villus and matures into a cystercoid larva. In the small intestines it envaginates its scolex (sucker), attaches to the mucosal and matures into an adult. H. nana are also capable of auto-infection where the mature worm releases its egg containing oncosphere in the intestines without passage through the external environment. This auto-infection results in high worm burdens in some individuals, in fact up to 1000 worms may be present in some individuals in heavy infestations.

Clinical Manifestations: H. nana infections are most often asymptomatic. Heavy infestations can cause abdominal pain, weakness, anorexia, and diarrhea.

Diagnosis: The diagnosis is made by identifying the egg form in stool preparations.

Treatment: Praziquantel is the drug of choice. Extended therapy with niclosamide is an alternate therapy.

Life Cycle Figure:

Egg of Hymenolepis nana. These eggs are oval or subspherical and smaller than those of H. diminuta, their size being 40 to 60 µm X 30 to 50 µm Images from CDC Website, Division of Parasitology

References:

Koneman et.al. Color Atlas and Textbook of Diagnostic Microbiology, 5^th Edition, Lippincott-Raven, Philadelphia, 1997
Centers for Disease Control Website, Parasitology division