Hymenolepis nana- Dwarf Tapeworm

Hymenolepiasis is caused by Hymenolepis nana (the dwarf tapeworm,a type of intestinal worm or helminth infecting humans, especially children.

1. Hymenolepisnana
AnupMuni Bajracharya

2. Causative agent
•Hymenolepisnana
•is also known as the dwarf tapeworm.
•The species name ‘nana’is derived from its small
size which meansdwarfof the adult worm.
•It is the smallest and only cestodethat parasites
the human without any intermediate host.
A.B

3. Habitat
•In human: The adult worm resides in the ileal
portion of the small intestine
•It is also present in other mammals like rats
and mice
A.B

4. Geographical Distribution
•The parasite is cosmopolitan in distribution.
•The worm is found in temperate than tropical
countries.
•It is highly prevalent in
•South Africa,
•South Europe ,
•Latin America and
•Middle-east Asia.
A.B

5. Morphology
•small and thread like worms
•measuring 1-4 cm in length with a diameter of
1mm.
•Body consists of a scolex, a long neck and
strobiliconsists of nearly 200 proglolttids.
A.B

6. •Scolex:
•globular, measuring 0.32
mm in diameter.
•four suckers and a short
rostellumarmed with 20-30
spines in one ring.
•Rostellumis retractable and
always remains invaginated
at the apex of the organ.
•Neck:
•It is relatively long and
situated posterior to the
head.
A.B

7. •Strobila
•consists of nearly 200 segments or proglottids.
•Each mature segment-0.3 mm in length by 0.9 mm breadth.
•Proglottidcontains both male and female reproductive organs.
•Genital pores are marginal and are situated on the same side.
•The uterus is a transverse sac with lobulatedwalls and there are three testes.
•Proglottidsneat the neck regions are small, short, narrow and immature and
those away from the scolexare mature and gravid.
•Segments at distal end are the gravid proglottids, which contain fertilized eggs.
A.B

8. •Eggs
•the infective form of parasite to
human.
•liberated in the faecesby gradual
disintegration of the terminal
segments.
•colorless, spherical or oval in shape,
•measuring 30-45mm in diameter.
•has 2 distinct membranes.
•Outer membrane -thin and colorless
•On inner membrane there are two
small “knobs” or poles from which 4–
8 filaments arise
•Inner membrane (embryophore)-
encloses an oncospherewith 3 pairs
of lancet shaped hookletsthat is
•they are embryonatedand have a 6-
hooked oncospheresinside the shells.
A.B

9. Life cycle
•Life cycle is completed in a single host, man and does not
require any intermediate host.
•Man and rat act as both definitive and intermediate hosts.
•Man acquires infections by injection of fully embroynated
egg.
•In the small intestine a hexacanthembryo is liberated.
•It borrows into the villiof the anterior part of the small
intestine and in about 4 days time develop into a typical
larval stage called ‘cysticercoid’.
•After reaching maturity the ileum ruptures and the larva
enters the lumen of the small intestine. Later, it attaches to
another villusfurther down and in the course of fortnight
develops into adult worms.
A.B

10. •The gravid proglolttidsbreaks off the adult worm and
disintegrate to release embryonatedeggs while it
passes down the intestinal tract.
•The eggs passed in the faecesare the source of
infection for new host and the cycle is continued.
•Sometimes, few eggs hatch out in the lumen of the
small intestine and liberate embryos which directly
invade the intestinal villi.
•This phase of infection is calledinternal
autoinfectionand is responsible for increased worms
load in intestine.
•Some person infect own self by faeco-oral route due to
bad personal hygiene.
•This is called external manifestation and is responsible
for persistence of the infection in a host.
A.B

11. A.B

12. Mode of transmission
•Infected human faecesare the chief source of
infection.
•Transmission of the man occurs-
•Through faecel-oral route by ingestion of eggs
from contaminated hands.
•Frequently by contaminated food and water
•Rarely from ingestion of food contaminated
fleas habouringthe cysticercoidlarva.
A.B

13. Pathogenesis
•Even large numbers of parasite is well tolerated.
•The mechanisms by which symptoms are usually
produced is an allergic reaction.
•In heavy infections large number of worms may
cause:
•Mechanical irritation of the intestine and produce
various clinical manifestation and
•Various allergic manifestation such as anal and
nasal pruritus(redness ,itching) by releasing toxic
metabolites.
A.B

14. Clinical manifestation
•Most infections are asymptomatic.
•In heavy infections, symptoms include irritability,
diarrhea, abdominal pain, sleep disorder, anal
pruritusand nasal pruritus.
•Rare symptoms anorexia, nausea and vomiting.
•Complications
•These include bloody diarrhea and behavioural
disturbances.
A.B

15. Laboratory diagnosis
•1.Specimen:
•Stool sample
•rectal swab
•2. Microscopy:
•Diagnosis is based on the demonstration of characteristics eggs in
the faecesby direct microscopy.
•The eggs can readily be concentrated by the salt flotation and
formalin ether sedimentation technique.
•3. Hematology:
•Eosiniphilaof more than 5% is seen in 1/3
rd
of the infected children
•4. Endoscopy:
•Adult worm can be identified during endoscopic examination
•5. ELISA:
•It has 80% sensitivity
A.B

16. Treatment
•Praziquantel: drug of choice
•Albendazole, Mebendazole
Prevention and control
•Sanitary improvements
•Uncontaminated food supplies
•Rodent control in house
•Personal hygiene
A.B

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A.B