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About this Database
Ecchinococcus Full-Length cDNA project
Yuzaburo OKU1, Junichi Watanabe2, Chihiro SUGIMOTO3,
Nariaki NONAKA1, Jun MASTUMOTO1, Hiroyuki WAKAGURI4,
Yutaka SUZUKI4, Sumio SUGANO4, Atsushi TOYODA5,
Yoshiyuki SAKAKI5, and Masao KAMIYA6
(1Graduate School of Veterinary Medicine, Hokkaido University,
2Institute of Medical science, The University of Tokyo,
3Research Center for Zoonosis Control, Hokkaido University
4Graduate School of Frontier Science, The University of Tokyo
5RIKEN Genomic Sciences Center, RIKEN
6OIE Reference Laboratory, Department of Biosphere and Environmental Sciences,
Faculty of Environment Systems, Rakuno Gakuen University
)
About this Database
Full-Echinococcus, a database for full-length cDNAs from a human parasite,
Echinococcus multilocularis, has been produced.
The full-length cDNA library was produced using the Vector-trapper method from
hydatid cysts developed in cotton rats that were infected with E.multilocularis.
A total of 10,966 5'end-one-pass sequences were compared with the non-redundant database
of DDBJ/Genbank/EMBL using BLAST and TBLASTX programs.
Two-thirds of the sequences were considered to be derived from Echinococcus,
while the remaining one-third represent host genes.
Many of the former clones represent full-length cDNAs that are expressed in the larva stage.
These clones are available for further analysis and experiments.
The parasite
Echinococcus is a small tapeworm (~4mm) which affects humans and causes hydatid cysts.
E.multilocularis and E.granulosus are the two most important species.
The disease
Echinococcus multilocularis is distributed in the northern region of the earth
(Europe, Russia, China, Japan and North America) and causes human alveolar hydatidosis.
The estimated number of patients worldwide is about 300,000. When a human becomes
infected by ingestion of eggs, the eggs develop into the metacestode stage in the liver,
proliferate asexually, infiltrate to the peripheral parts of the liver and
metastasize to other organs. Alveolar hydatidosis is a malignant and fatal disease in humans.
The most effective therapy at present is surgical removal.
Life cycle of E.multilocularis (Fig. 1)
The parasite requires two mammalian hosts for completion of the life cycle;
the definitive hosts, dogs and foxes, and intermediate hosts, mostly rodents.
Egg-containing gravid segments of the parasite or free eggs are voided
with the feces of the definitive hosts. Intermediate hosts become infected
by ingestion of eggs, which hatch in the digestive tract, penetrate the small intestine,
migrate to the liver and develop into metacestodes (larval stage, Fig. 2).
The metacestodes form a huge number of minute cysts which consist of an outer
laminated acellular layer and an inner nucleated germinal layer. In some minute cysts,
brood capsules contain protoscoleces. Though the time course is variable,
it usually takes two to three months before protoscoleces form in rodents.
Connective tissues and inflammatory cells of the host surround the metacestodes.
They proliferate actively by external budding of minute cysts.
When the definitive hosts prey on the intermediate hosts, protoscoleces become established,
develop to adults in the small intestine and produce eggs after a month.
Increased prevalence of Echinococcosis in Hokkaido, Japan
Between 1937 and 2004, a total of 482 persons were diagnosed with alveolar hydatidosis in Hokkaido, Japan.
Between 2000 and 2005, eleven to 28 new patients were reported every year.
The prevalence of adult E.multilocularis in red foxes in Hokkaido increased
from 10% in 1985 to 46% in 2005. The prevalence in dogs and cats was 1 and 5.5%, respectively.
Intermediate hosts included rodents, insectivores, horses, pigs and zoo animals
(gorilla, orangutan, Japanese macaque). The prevalence in pigs was 0.07% in 1996 and 0.25% in 2006.
The potential for expansion of the endemic area to the main island of Japan is of great concern.
Control trial in Japan
We have undertaken a comprehensive program to control the source of infection, i.e.,
infected definitive hosts. We developed a novel method to detect the parasite coproantigen
in the feces of red foxes. Using this non-invasive method, we successfully surveyed
E.multilocularis infection in wild red foxes, and house dogs in urban area of,
Sapporo and in a rural area, the Koshimizu district in northeastern Hokkaido.
We have initiated a deworming program using praziquantel in the wild red foxes
in the Koshimizu district under close monitoring of infection dynamics by coproantigen detection.
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| Fig. 1 Life cycle |
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Definitive hosts are red foxes, dogs and cats, which prey on intermediate hosts, mainly voles,
containing metacestodes (protoscoleces). In the intestine of the definitive hosts the parasites
develop to adult tapeworms (left: a micrograph of an adult stained with carmine;
right: non-stained worms in a petri dish). Adults produce eggs which are voided with feces.
They are infective to intermediate hosts. Eggs have thick embryophores and contain six-hook oncospheres.
Eggs ingested by rodents develop to metacestodes which produce numerous protoscoleces.
The inset shows a micrograph of protoscoleces. Left: intact; right: evaginated.
Humans, pigs and horses are accidental and unsuitable intermediate hosts.
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| Fig. 2 Larva |
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Alveolar hydatid cysts are formed in the livers of rodents.
Brood capsules with protoscoleces are seen in some small cysts,
while many minute cysts contain no protoscoleces (PAS-haematoxylin stain).
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