Hymenolepis nana - Life Cycle, Pathogenesis, Pathology, Host Immunity, Clinical Manifestation, Laboratory Diagnosis

Life Cycle of Hymenolepis nana

Hymenolepis nana is the only cestode that does not require any intermediate host and the life cycle is completed in a single host. The definitive host includes humans, a rat, and a mouse.

• humans become infected after ingestion of Hymenolepis nana eggs

• once in the small intestine, the embryo (oncosphere) is released from the egg

• the oncosphere penetrates the small intestine and within 5 days, it develops into a small larval stage (cysticercoid)

• after fully maturing, the larva travels back to the small intestinal lumen where it attaches itself to the wall of the intestine with the help of suckers

• within a month of infection, the tapeworm rapidly develops into an adult and the gravid proglottid breaks off and disintegrates to release fertilized eggs

• these eggs are passed out along with the host feces which is the source of infection for new hosts (direct infection)

• in some cases, the eggs hatch in the small intestine lumen of the original host to release embryos in the process called internal autoinfection

• autoinfection is responsible for the tremendous increase in the number of tapeworms in the intestine

• external autoinfection may also occur- which occurs when a person ingests eggs dispersed from their own body via the fecal-oral route and is mostly due to a lack of personal hygiene

• moreover, external autoinfection is responsible for the persistence of Hymenolepis nana infection

• by the process of direct infection, internal or external autoinfection, the life cycle of Hymenolepis nana continues

Pathogenesis, Pathology of Hymenolepis nana

Infection by cysticercoid larvae of Hymenolepis nana in the intestine shows little to no pathology. However, in heavy cases of infection, pathological changes include:

• mechanical irritation of the intestine

• release of toxic metabolites results in various allergic manifestations including anal and nasal pruritus

Host Immunity of Hymenolepis nana

If Hymenolepis nana infection is acquired by direct cycle, it evokes a strong humoral and cellular response from the host body. The host immunity provides protection from subsequent infection by the same tapeworm.

But the immune system is unable to remove adult worms that have attached and invaded the gut wall.

Clinical Manifestations of Hymenolepis nana

Hymenolepiasis is more common in children (age 4-10 years) than in adults, mostly due to a lack of proper regular hygiene.

• the incubation period is between 15 days to 39 days

• mostly asymptomatic

• in cases of heavy infections, symptoms include abdominal irritation, diarrhea, abdominal pain, anal pruritis, nasal pruritis, and sleep disorders

• in rare cases, symptoms include nausea, vomiting, anorexia

Laboratory diagnosis of Hymenolepis nana

Sample

• Stool

Microscopy

Direct wet mount microscopy

• the presence of Hymenolepis nana eggs in stool samples confirms the infection

• the wet mount is prepared by mixing the sample with saline, iodine, or lactophenol cotton blue (LPCB)

Examination of a stool after concentration

• formalin-ethyl acetate and salt floatation concentration methods are used to concentrate the stool so that the parasites have increased yield

Treatment of Hymenolepis nana

Drugs of choice include praziquantel, niclosamide, and paromomycin. Due to the presence of a large number of tapeworms due to autoinfection and the presence of cysticerci, repeated treatment is required for a period of two weeks.

Prevention, Control of Hymenolepis nana

Individual prophylaxis

• improved personal hygiene such as proper washing of hands with soap after defecation and before eating food

• treatment of water before drinking such as boiling, filtering the water used in a 0.22-micrometer membrane, iodination with tetracycline hydro per iodide

• drinking bottled water while traveling to areas endemic to hymenolepiasis as chlorine treatment cannot kill the eggs

• if salad is to be consumed, treat the vegetables with acetic acid or vinegar for 15 minutes

• not performing sexual acts that involve fecal-oral contact

Community prophylaxis

• improvement of the water management system to avoid fecal contamination

• improvement of sanitation by installing latrines for proper disposal of human feces