Submitted by Thikra Abdullah Mahmood
Causal Agents of Hymenolepiasis :
Hymenolepiasis is caused by two cestodes (tapeworm)
species, Hymenolepis nana (the dwarf tapeworm, adults
measuring 15 to 40 mm in length) and Hymenolepis
dimnuta (rat tapeworm, adults measuring 20 to 60 cm in
length). Hymenolepis diminuta is a cestode of rodents
infrequently seen in humans and frequently found in
rodents.
Life Cycle:
Eggs of Hymenolepis nana are immediately infective when
passed with the stool and cannot survive more than 10
days in the external environment
. When eggs are
ingested by an arthropod intermediate host
(various
species of beetles and fleas may serve as intermediate
hosts), they develop into cysticercoids, which can infect
humans or rodents upon ingestion
and develop into
adults in the small intestine. A morphologically identical
variant, H. nana var. fraterna, infects rodents and uses
arthropods as intermediate hosts. When eggs are ingested
(in contaminated food or water or from hands
contaminated with feces), the oncospheres contained in
the eggs are released. The oncospheres (hexacanth
larvae) penetrate the intestinal villus and develop into
cysticercoid larvae
. Upon rupture of the villus, the
cysticercoids return to the intestinal lumen, evaginate their
scoleces
, attach to the intestinal mucosa and develop
into adults that reside in the ileal portion of the small
intestine producing gravid proglottids
. Eggs are passed
in the stool when released from proglottids through its
genital atrium or when proglottids disintegrate in the small
intestine
. An alternate mode of infection consists of
internal autoinfection, where the eggs release their
hexacanth embryo, which penetrates the villus continuing
the infective cycle without passage through the external
environment
. The life span of adult worms is 4 to 6
weeks, but internal autoinfection allows the infection to
persist for years.
Eggs of Hymenolepis diminuta are passed out in the feces
of the infected definitive host (rodents, man)
. The
mature eggs are ingested by an intermediate host (various
arthropod adults or larvae)
, and oncospheres are
released from the eggs and penetrate the intestinal wall of
the host
, which develop into cysticercoid larvae.
Species from the genus Tribolium are common
intermediate hosts for H. diminuta. The cysticercoid larvae
persist through the arthropod's morphogenesis to
adulthood. H. diminuta infection is acquired by the
mammalian host after ingestion of an intermediate host
carrying the cysticercoid larvae
. Humans can be
accidentally infected through the ingestion of insects in
precooked cereals, or other food items, and directly from
the environment (e.g., oral exploration of the environment
by children). After ingestion, the tissue of the infected
arthropod is digested releasing the cysticercoid larvae in
the stomach and small intestine. Eversion of the scoleces
occurs shortly after the cysticercoid larvae are released.
Using the four suckers on the scolex, the parasite attaches
to the small intestine wall. Maturation of the parasites
occurs within 20 days and the adult worms can reach an
average of 30 cm in length
. Eggs are released in the
small intestine from gravid proglottids
that disintegrate
after breaking off from the adult worms. The eggs are
expelled to the environment in the mammalian host's feces
.
Geographic Distribution:
Hymenolepis nana is the most common cause of all
cestode infections, and is encountered worldwide. In
temperate areas its incidence is higher in children and
institutionalized groups. Hymenolepis diminuta, while less
frequent, has been reported from various areas of the
world.
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Epidemiology of Hymenolepis Nana Infections of
Punjabi Villagers in West Pakistan
A temporal study of Hymenolepis nana infections in man in an endemic
area was conducted in the Punjab Region of West Pakistan. Infection
rates were highest in the age-group 2 to 19 years and transmission
appeared to be hand-to-mouth rather than through a rodent reservoir. The
optimum time for transmission appeared to be during the warmer months
of the year (May to October) which coincided with the greatest amount of
rainfall. Although the prevalence of H. nana in our study group of 93
children and adolescents was similar at the beginning and end of the study
which covered 22 months, there was an active turnover of this parasite in
the study group. That H. nana can persist in man in endemic areas for
long periods of time was demonstrated by the fact that 26% of the
participants were infected for the entire study period. There appeared to
be no correlation between systemic disturbances, such as those indicated
by diarrheal stools or abnormal eosinophil counts, and H. nana infections.
*
.
.
Hymenolepis nana Control

World-wide incidence 4%

Treatment usually Praziquantel previously
Niclosamide (both single oral dose)

Health education

Rodent reservoir?
Screening for activity against H. nana
H. nana in mice
Used because - Human infection—easily maintained in mice - Armed
scolex similar to other pathogenic tapeworms - Corresponds to other
tapeworms in its sensitivity to standard anthelmintics
Methods
Mature worms collected from infected mice
Terminal gravid proglottids removed, crushed
under coverslip—eggs removed
Eggs containing hooklets (mature) counted 0.2 ml stock soln. containing
1000 eggs/ml given to each mouse. Adult worm develops- 15-17 days.
Test drug given orally – autopsied on 3rd day Std. drug given Intestine
examined under dissecting microscope for worms/ scolex Response – no.
of mice cleared.
Symptoms
It is not clear that hymenolepiasis necessarily have any symptoms. The
symptoms of hymenolepiasis are traditionally described as abdominal
pain, loss of appetite (anorexia), itching around the anus, irritability and
diarrhea. However, in one study of 25 patients conducted in Peru,
successful treatment of the infection made no significant difference to
symptoms.[2] Some authorities report that heavily infected cases are more
likely to be symptomatic.[3][4]
Signs and tests
Examination of the stool for eggs and parasites confirms the diagnosis.
The eggs and proglottids of H. nana are smaller than H. diminuta.
Proglottids of both are relatively wide and have three testes. Identifying
the parasites to the species level is often unnecessary from a medical
perspective, as the treatment is the same for both.
Treatment
Praziquantel as a single dose (25 mg/kg) is the current treatment of choice
for hymenolepiasis and has an efficacy of 96%. Single dose albendazole
(400 mg) is also very efficacious (>95%). Niclosamide has also been
used.
A three-day course of nitazoxanide is 75–93% efficacious. The dose is 1g
daily for adults and children over 12; 400mg daily for children aged 4 to
11 years; and 200mg daily for children aged 3 years or younger.[2][5][6]
Prognosis
Cure rates are extremely good with modern treatments, but it is unclear
that successful cure results in any symptomatic benefit to patients.[2]
Complications


abdominal discomfort
dehydration from prolonged diarrhea
Prevention
Good hygiene, public health and sanitation programs, and elimination of
rats help prevent the spread of hymenolepiasis.
Source

Hymenolepiasis. Medline Plus.
References
1. ^ a b Zimmer, Carl (2001). Parasite rex: inside the bizarre world of
nature's most dangerous creatures. New York: Simon & Schuster.
ISBN 0-7432-0011-X.
2. ^ a b c Chero JC, Saito M, Bustos JA, et al. (2007). "Hymenolepis
nana infection: symptoms and response to nitazoxanide in field
conditions.". Trans R Soc Trop Med Hyg 101 (2): 203–5.
doi:10.1016/j.trstmh.2006.04.004.
3. ^ Chitchang S, Plamjinda T, Yodmani B, Radomyos P. (1985).
"Relationship between severity of the symptom and the number
of Hymenolepis nana after treatment.". J Med Assoc Thai 68: 423–
26.
4. ^ Schantz PM. (1996). "Tapeworm (cestodiasis).". Gastroenterol
Clin North Am 25: 637–53.
5. ^ Ortiz JJ, Favennec L, Chegne NL, Gargala G. (2002). "Comparative
clinical studis of nitazoxanide, albendazole and praziquantel in the
treatment of ascariasis, trichuriasis, and hymenolepiasis in
children from Peru". Trans R Soc Trop med Hyg 96: 193–96. PMID
12055813.
6. ^ Reomero-Cabello R, Guerro LR, Munez-Gracia MR, Geyne Cruz A.
(1997). "Nitazoxanide for the treatment of intestinal protozoan
and helminthic infections in México.". Trans R Soc Trop Med Hyg
91: 701–3.