Hymenolepis nana

Hymenolepis nana, commonly known as the dwarf tapeworm, is a cyclophyllid cestode that primarily infects humans and rodents. It is the most common tapeworm in humans, especially in children. Unlike other cestodes, H. nana does not always require an intermediate host for its transmission.

Morphology

Hymenolepis nana is a small tapeworm, measuring 15–40 mm in length and 1 mm in width. The scolex possesses four suckers and a retractable rostellum armed with a single row of hooks. The proglottids are wider than long, with genital pores on the same side. Eggs are oval, pproximately 30–50 µm in diameter, and contain an oncosphere with six hooklets enclosed in a thin,  membranous shell.

Life Cycle

The life cycle of H. nana can be direct (without an intermediate host) or indirect (with an intermediate host like fleas or beetles).

Egg Ingestion: Humans acquire the infection by ingesting embryonated eggs in contaminated food, water, or hands.

Hatching in Intestine: The eggs release oncospheres in the small intestine, which penetrate the intestinal villi.

Cysticercoid Development: Inside the villi, the larvae develop into cysticercoid larvae in 4–5 days. The cysticercoids rupture into the lumen and mature into adult tapeworms.

Adult Tapeworm and Egg Release: The mature worms produce eggs that are passed in feces. Autoinfection can occur when eggs hatch before being excreted, leading to persistent infections.

Indirect Life Cycle: In some cases, insects ingest the eggs, and humans become infected by consuming infected arthropods.

Prevalence and Epidemiology

1.       H. nana is globally distributed, with higher prevalence in tropical and subtropical regions.

2.       Common in children due to poor hygiene practices.

3.       Transmission occurs via fecal-oral contamination, especially in crowded and unhygienic conditions.

Pathogenicity

1.       Light infections may be asymptomatic.

2.       Heavier infections can cause: Abdominal pain, Diarrhea, Anorexia and weight loss, Irritability and sleep disturbances

3.       Auto-reinfection can lead to chronic infection and severe symptoms.

Diagnosis

1.       Microscopic Examination: Identification of characteristic eggs in stool samples.

2.       Concentration Techniques: Methods like formalin-ether sedimentation can enhance detection.

3.       Serological Tests: Less commonly used but can support diagnosis in cases of low parasite load.

Prophylaxis

1.       Maintaining proper hygiene and sanitation.

2.       Washing hands thoroughly before eating and after using the toilet.

3.       Avoiding consumption of contaminated food and water.

4.       Controlling insect vectors to prevent indirect transmission.

Treatment

1.       Praziquantel (single dose of 25 mg/kg) is the drug of choice.

2.       Nitazoxanide (alternative treatment) may be effective.

3.       Preventive measures and proper hygiene are essential to avoid reinfection.

References

1.      Garcia, L. S. (2021). Diagnostic Medical Parasitology. ASM Press.

2.      Centers for Disease Control and Prevention (CDC). (2023). "Hymenolepiasis." https://www.cdc.gov

3.      Roberts, L. S., & Janovy, J. (2020). Foundations of Parasitology. McGraw-Hill Education.

4.      WHO (2023). "Hymenolepis nana." World Health Organization Website. https://www.who.int