• smallest tapeworm infecting man
• does not require an obligatory intermediate host
• man can harbor both adult and larval stages of parasite
DISTRIBUTION
• worldwide among children
DISEASES
• hymenolepiasis
MORPHOLOGY
1. Adult Worm
- found in the ileum
- delicate strobila that measures 25 to 45 mm x 1 mm (lw)
- Scolex
o Subglobular
o 4 cup-shaped suckers
o retractable rostellum with a single row of 20 to 30 y-shaped hooklets
- Neck
o long and slender
- Proglottids
o Anterior = short
o Posterior = broader
o Measures 0.15 to 0.3 mm x 0.8 to 1.0 mm (lw)
o Mature proglottids : contain 3 ovoid testes and one ovary
o Gravid proglottids :
testes and ovary disappear
uterus hollows out and becomes filled with eggs
segments are separated from the strobila and disintegrate as they pass out of the intestines, releasing eggs in stool
- Segments
o 175 to 220 segments
o genital pores found along the side of segments
2. Eggs
- Shape : spherical or subspherical
- Measures 30 to 47 um in diameter
- Oncosphere
o thin outer membrane
o thick inner membrane with conspicuous bipolar thickenings
4 to 8 hair-like polar filaments arise
filaments are embedded in the inner membrane
H. nana cysticercoid
LIFE CYCLE
- Dual pathway
1. Direct
• host ingests eggs which hatch in the duodenum
• liberated embryos penetrate mucosal villi
• develop into infective cysticercoid larvae
• larvae break out of villi and attaches to intestinal mucosa 4 to 5 days later
• develop into adults
2. Indirect
• infection is usually via accidental ingestion of infected arthropod intermediate hosts like rice and flour beetles (Tenebrio sp.)
• cysticercoid larvae are released and will eventually develop into adult tapeworms in the intestines of the host
- takes 20 to 30 days from time of ingestion for eggs to appear in the feces
- eggs are viable immediately after discharge from bowel
- autoinfection can occur through the fecal-oral route or w/in the small bowel
- oncospheres from eggs are released and they invade the host villi to start new generation
PATHOGENESIS AND CLINICAL MANIFESTATION
• symptoms are produced because of patient’s immunological response to the presence of the parasite
• asymptomatic – light worm burden
• clinical manifestations:
o headache
o dizziness
o anorexia
o pruritus of nose and anus
o diarrhea
o abdominal pain
o pallor
• infected children
o restless
o irritable
o exhibit sleep disturbances
o convulsions (rare)
• Heavy infections
o Enteritis due to necrosis and desquamation of the intestinal epithelial cells
• Regulatory immunity
o (time) clears H. nana spontaneously.
DIAGNOSIS
• specific diagnosis = demonstration of characteristic eggs in stool
• light infections = need to concentrate stool specimens
• proglottids are not recovered because they undergo degeneration prior to passage with stools
TREATMENT
• *Praziquantel = 25mg/kg single dose
o causes vacuolization and disruption of tegument in the neck region
o dosage for hymenolepiasis is higher than for taeniasis because of relative resistant cysticercoids in the intestinal tissue
• examine stool after 2 weeks
o repeat treatment to cover for the worms emerging from remaining viable cysticercoids
EPIDEMIOLOGY
• found in warm countries
o Southern USA
o Latin America
o Mediterranean
o East Asia
o Philippines
• Transmission : poor sanitation, overcrowding, poor personal hygiene
• Direct contact plays an important role because eggs cannot survive long outside host
• Familial and institutional infection
• Found in mice and rats
PREVENTION AND CONTROL
• involves a single host and transmission is direct
• personal hygiene and environmental sanitation
• rodent control
• prevent food from infections by grain beetles
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BIVEK SINGH
