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| Adult E. granulosus [7 |
Echinococcus granulosus is a cyclophylid cestode that parasitizes the small
intestines of canids as adult and causes hydatid disease in humans and
livestock in its intermediate hosts during its larvae stage. Effect of the
parasite in canids is less than in its intermediate hosts.[3] "Echinococcus
granulosus is found worldwide, mostly in rural and grazing areas." The most common treatment against hydatid disease in humans is to remove the
hydatid disease through surgery. The treatment is notalways hundred percent
successful because the cysts can burst resulting in spreading the cysts or
cause allergic reactions.[1][2] “Human infection of
hydatid disease can be prevented if people are made aware of the risks and the
proper safety precautions are taken.” [2]
Symbiont Description
E. granulosus is
from the phylum Platyhelminthes, the class Cestoda, the order Cyclophyllidea,
the family Taeniidea, and the genus Echinococcus. “This small tapeworm
grows to about is 3- 6mm long, and lives in the small intestine of canines.”
It body includes a scolex with suckers and hooks that allows it to gain
nutrients by attaching itself to the mucisal wall of the host. “The head and
the three proglottids are connected by a short neck; proglottids are the body
segments of the worm which contains the eggs that will be excreted in the
feces. “[2]
Host Description
Bowflies, birds, arthropods serve as mechanical vectors of eggs
of the parasite. Then, the eggs are
consumed by the intermediate hosts; livestock such as sheep, goat, swine,
cattle, horses and camel serve as the intermediate hosts of the parasite. E.
granulosus matures in its definite hosts after the definite hosts
consume an infected livestock; dogs or other canids serve as definitive hosts. E.
granulosus can also parasitize humans. [1][2] Humans
serve as dead-end intermediate host.
Life Cycle
“The [matured] E. granulosus live in
the small bowel of the definitive hosts such as a dog.” The hydatid worms
releases eggs that are passed in dog feces. The intermediate host consumes
the feces then, the eggs hatches in the bowel of the Intermediate host. Afterwards,
“the egg releases an oncosphere that penetrates the intestinal wall and
migrates through the circulatory system of the intermediate host into various
organs, especially the liver and lungs. Within these organs, the
oncosphere develops into a cyst.” As the
cysts develop, “protoscolices and daughter cysts fill the interior of the cysts.”
The parasite is transmitted to the definite host by consumptionof organs of the
intermediate host containing systs. After trransmittance, “the
protoscolices turns insode out, attach to the intestinal mucosa, and
develop into adult stages within 32 to 80 days and the cycles continues.”
Humans are infected by E. granulosus by consuming the eggs. The
parasite develops and matures in the intestine and other organs but is not able
to transfer to other hosts.[1][5]
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| Life cycle of E. granulosus [1] |
Ecology
There are few available data on the clinical effects of the
Cystic Hydatid Disease in the intermediate hosts since the cyst is slow in
growing and animals are often slaughtered before it manages to create
sufficient pressure on the tissue or organs.[3] The adult hydatid
worm heavily affects its definite host when in large numbers which results in severe
enteritis. Some dogs have developed immunity against the effects of E.
granulosus.[4] “Since E. granulosus mechanical
vectors can increase the chances of eggs being ingested by the grazing animals
through mechanical dispersal, E. granulosus can be
very epidemiological; a single dog can infect many sheep over a wide area.”[3]
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| Large daughter cysts [8] |
“In Humans, Echinococcus granulosus infections
remain silent for years before the enlarging cysts cause symptoms in the
affected organs. If the cyst(s) bursts, the resultant toxic
(anaphylactic) shock would probably be fatal.” [5] “Infected
humans cannot transmit E. granulosus” to other humans. [1]
“Hydatid disease is more prevalent in the northern
hemisphere. Human infection is most common in sheep-raising countries
such as Australia and New Zealand, throughout England and Europe, the Middle
East, Russia, Northern China, and Japan. In the Americas the disease is
especially prevalent in the Southern countries such as Argentina, Uruguay and
Chile, and also occurs in Alaska and Canada. The incidence of human
infection about 1 to 2 per 1000 population and may be higher in rural areas of
affected regions.”[2]
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| Global distribution of E. granulosa (black) [6] |
Example of Host Resistance
“The natural hosts
of E. granulosus have developed a natural resistance to the
hydatid worm. Natural hosts have slowly developed some immunity against
the parasite thus limiting the effects of the parasite; the definitive hosts
needs to be heavily infected the parasite in other for the parasite to be
harmful to the host. E. granulosus don’t usually cause
harm to its intermediate hosts except for humans.”[4] “The low
virulence of E. granulosus in natural hosts reduces its
potential as an important limiting factor on the population of the host.” [5]
References
Gloria, the Author. Please if you recieve this comment please contact me! I believe I have this ! I have pictures . A cyst ruptured inside me i need help and the Drs in Ar think I am crazy.
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