Hymenolepis is a genus of cyclophyllid tapeworms responsible for hymenolepiasis. They are parasites of humans and other mammals. The focus in this article is in Hymenolepis commonly parasitizing humans.
Most infections do not have many worms and therefore can have no symptoms. Patients with more than 15,000 eggs per gram of stool may experience cramps, diarrhea, irritability, anorexia, or enteritis caused by cystercoids destroying the intestinal villi in which they develop. [1]
Hymenolepiasis is the most common cestode infection in humans. Infections are seen more often among children. It is most widespread in warm climates and around unsanitary areas where eggs can be passed through fecal matter from an infected host to an uninfected person.
Hymenolepiasis is caused by the introduction of either tapeworm species Hymenolepis nana (H. nana) or Hymenolepis diminuta (H. diminuta) into the human body. A member of the cestode class, tapeworms do not have digestive tracts to absorb nutrients, instead their surface body layer is metabolically active with nutrients and waste passing in and out continuously. In contrast, the nematodes class, such as hookworms, have complete digestive tracts and separate orifices for food ingestion and waste excretion. Although the cestode life cycle requires the cysticercoid, or larval, phase to be developed in an intermediate host, H. nana does not follow this observation and can use an intermediate host or auto infect the human host.
Hymenolepis nana is an auto-infecting parasite that does not require an intermediate host. It can, however, grow in rats as well. The fertilized eggs pass in the stool from an infected host. The eggs are then either eaten by an insect or by a human which mainly occurs through the ingestion of contaminated food or water. The cysticercoid stage develops either outside the body in an insect that can then be eaten by a human or a rat, or it develops in the intestinal villus of an auto-infected human. The adult phase begins with the growth of the scolex with several hooks. After attaching itself to the intestinal wall and growing proglottids, fertilized eggs can pass in the host’s stool as the gravid proglottids deteriorate and release eggs. [3]
Hymenolepis diminuta fertilized eggs pass in the stool from an infected host. The eggs are then eaten by grain beetles where the cysticerci, or larval stage develops. Humans then can eat the bug or its mealworm phase in cereal or flour. The worm matures in the duodenum, the first portion of the small intestine, and attach to the mucosa lining. Fertilized eggs can pass in the host’s stool as the gravid proglottids deteriorate and release eggs. [3]