Hymenolepis Nana

Hymenolepis nana is the smallest of all tapeworms found in humans and is appropriately described as the dwarf tapeworm. It is the only cestode that does not require an intermediate host to develop into its infective stage. A common intermediate host, however, is the grain bettle. Adult worms can be found in the proximal ileum of the small intestine and are usually only a couple of centimeters long. Only the scolex is attached to the mucosa of the small intestine, and after about two weeks, the gravid segments will drop off into the lumen. This release will allow eggs to enter into the host's feces, and thereby contanimating the external environment. Some eggs, however, may remain in the small intestine making autoinfection a likely probability. After accidental ingestion, eggs will travel to the small intestine of their hosts where they will hatch in the duodenum. The oncosphere will infiltrate the villa of the intestinal lining, and soon after will become a cysticercoid larva. After four to five days, this infective larva will break free into the lumen of the small intestine and travel to the ileum where it will reattach itself to the intestinal mucosa. Within the next five days it will develop into a full adult worm. Besides humans, the house mouse is another possible definitive host.

adult H.nana

(courtesy of CDC Division of Parasitic Diseases) http://www.dpd.cdc.gov/dpdx/HTML/Hymenolepiasis.htm

 

 

 

References
Heyneman, Donald. Cestodes. 4 June 2005 <http://gsbs.utmb.edu/microbook/ch089.htm>.
Markell, Edward et al. Medical Parasitology. Philadelphia, PA: Sanders, 1999.
General Practice Notebook. Oxbridge Solution Ltd, 2005. 4 June 2005 <http://www.gpnotebook.co.uk/simplepage.cfm?ID=-778436586>.