Hymenolepis diminuta is a small parasitic worm (tapeworm) commonly found in rats and mice. Their distribution is worldwide, they have been reported in temperate to tropical environments, and particularly in places with poor sanitation.
Basically H. diminuta is a parasite of rats but it is important to note that some sporadic cases of human infections have been described.
Infection rates according to different surveys vary between 0.001% and 5.5%. For its part, Hymenolepis nana, is the tapeworm that causes infections in humans with the highest incidence.
Later, the oncospheres (larvae) are released from the eggs that penetrate the host's intestinal wall and develop into cysticerci (cyst-shaped larvae), the infectious form of this worm.
Cysticercoid larvae persist through arthropod morphogenesis into adulthood. H. diminuta infection is acquired by the mammalian host (mouse or human) when it ingests the intermediate host (arthropod) that carries the cysticercoid larvae.
Humans can be accidentally infected by ingesting insects on convenience foods or other foods, as well as directly from the environment. For example, young children when orally exploring their environment.
After ingestion, the infected arthropod tissue is digested, thus releasing the cysticerci in the stomach and small intestine of the mammalian host.
After the cysticercoid larvae are released, they project cephalic structures called scoleces that serve to adhere to the host's small intestine.
Maturation of the parasites occurs in the first 20 days and the adult worms reach an average of around 30 cm in length.
The eggs are released into the small intestine from gravid proglottids (serially repeated bisexual reproductive segments) that disintegrate after being separated from the body of adult tapeworms.
The eggs are expelled into the environment in the feces of the mammalian host, starting the cycle again.
Symptoms
The human form of H. diminuta infection is often asymptomatic, but some cases have been reported where patients developed abdominal pain, irritability, itching, and eosinophilia.
This last symptom refers to the atypical increase in leukocytes (white blood cells) which are the cells of the immune defense.
Diagnosis
Infections in humans are usually indicated by observing the presence of eggs in the stool.
References
- Hancke, D., & Suárez, OV (2016). Infection levels of the cestode Hymenolepis diminuta in rat populations from Buenos Aires, Argentina. Journal of Helminthology, 90 (90), 199–205.
- Mansur, F., Luoga, W., Buttle, DJ, Duce, IR, Lowe, A., & Behnke, JM (2016). The anthelmintic efficacy of natural plant cysteine proteinases against the rat tapeworm Hymenolepis diminuta in vivo. Journal of Helminthology, 90 (03), 284–293.
- Marangi, M., Zechini, B., Fileti, A., Quaranta, G., & Aceti, A. (2003). Hymenolepis diminuta infection in a child living in the urban area of Rome, Italy. Journal of Clinical Microbiology, 41 (8), 3994–3995.
- Roberts, L. (1961). Influence of Population Density on Patterns and Physiology of Growth in Hymenolepis diminuta (Cestoda: Cyclophyllidea) in the Definitive Host. Experimental Parasitology, 11 (4), 332–371.
- Tena, D., Gimeno, C., Pérez, T., Illescas, S., Amondarain, I., González, A., Domínguez, J. & Bisquert, J. (1998). Human Infection with Hymenolepis diminuta: Case Report from Spain. Journal of Clinical Microbiology, 36 (8), 2375–2377.
- Tiwari, S., Karuna, T., & Rautaraya, B. (2014). Hymenolepis diminuta Infection in a Child from a Rural Area: A Rare Case Report. Journal of Laboratory Physicians, 6 (1), 58–59.
- Yang, D., Zhao, W., Zhang, Y., & Liu, A. (2017). Brown Rats (Rattus norvegicus) in Heilongjiang Province, China. The Korean Journal of Parasitology, 55 (3), 351–355.