2. Introduction
Echinococcus granulosus, also called hydatid worm
belongs to class Cestoda
It causes cystic echinococcosis in livestock and
humans being intermediate hosts and parasitize the
small intestines of adult canids
It is a zoonotic disease
Definitive hosts are carnivorous predators like dogs,
wolves, foxes and lions. While sheep, goat, cattle, pigs
and rodents are intermediate hosts. Birds and
arthropods act as mechanical vectors
3. Classification
Kingdom : Animalia
Phylum : Platyhelminthes
Class : Cestoda
Sub Class : Eucestoda
Order : Cyclophyllidea
Family : Taenidae
Genus : Echinococcus
Species : Echinococcus granulosus
4. Morphology
The adult tapeworm ranges in length from 2 mm to
7 mm and has three proglottids when intact — an
immature proglottid, mature proglottid and a gravid
proglottid.
It has scolex with four suckers and also has a rostellum
with hooks.
Echinococcus is triploblastic, anus is absent and it has
no digestive system.
Its body is covered by tegument and the worm is
divided into a scolex, a short neck, and three to six
proglottids. Its body shape is ribbon-like.
5. Transmission
Adult E. granulosus release eggs within the intestine
which will be transported out of the body via feces
When contaminated waste is excreted into the
environment, intermediate host has the potential to
contract the parasite by grazing in contaminated
pasture
It is transmitted from the intermediate host (sheep) to
the definitive host (dogs) by frequent feeding of offal.
Consuming offal containing Echinococcus
granulosus can lead to infection
6. Life cycle
The adult is in the small intestines of the definitive
host (dogs)
Gravid proglottids release eggs that are passed in the
feces
The intermediate hosts are infected by ingesting eggs,
the egg hatches in the small bowel and releases an
oncosphere
The oncosphere penetrates the intestinal wall and
moves through the circulatory system to various
organs
In the organs they develop into cysts and enlarge
gradually
7. The cysts produce protoscolices and daughter
cysts
Definitive host eats the infected organs and
becomes infected
After ingestion, the protoscolices evaginate, attach
to the intestinal mucosa and develop into adult
stages
In 32-80 days, cycle starts over
8.
9. Pathogenesis
Ingested eggs from animal hatch in the gut and release
oncospheres
Oncospheres penetrate the intestinal wall, migrate via the
circulation, and lodge in the liver or lungs or, less
frequently, in the brain, bone, or other organs.
In tissue , E. granulosus oncospheres develop into cysts,
which grow slowly (usually over many years) into large
fluid-filled lesions—hydatid cysts
Large cysts may contain >1 L of highly antigenic hydatid
fluid as well as millions of protoscolices
If a cyst in the liver leaks or ruptures, infection can spread
to the peritoneum.
10. Signs
Signs depend upon the site of infection
Liver cysts cause abdominal pain or a palpable mass.
Jaundice may occur if the bile duct is obstructed.
Rupture into the bile duct, peritoneal cavity, or lung
may cause fever, urticaria, or a serious anaphylactic
reaction.
Pulmonary cysts can cause cough, chest pain, and
hemoptysis.
Brain and spinal cord; cause epilepsy and blindness
11. Diagnosis
Diagnosis in the definitive host, the dog, is difficult by
ordinary microscopy as it cannot demarcate
between Taenia and Echinococcus eggs
Detection of antigens in feces by ELISA is currently the
best available technique
Other techniques are;
Imaging
Serologic testing
Examination of cyst fluid
13. Treatment
Surgical Removal of Hydatid Cysts 90% effective but can be
risky depending on location, size, and advancement of cyst
It may need chemotherapy to prevent recurrance
Chemotherapy: Albendazole is preferred treatment
because it penetrates into hyatid cysts. Dosage: 10mg/kg
body weight or 400mg 2x daily for 4 weeks
Mebendazole Dosage: 40mg/kg body weight 3x daily for 3-
6 months
Dogs are effectively treated with Praziquental
PAIR Treatment Puncture, aspiration, injection, respiration
Inject protoscolicidal substances into the cyst
14. Prevention
In order to prevent transmission to dogs from
intermediate hosts, dogs can be given anthelminthic
vaccinations
Clean slaughter and high surveillance of potential
intermediate host during slaughter is key in preventing
the spread this cestode to its definitive host
Proper disposal of carcass and offal after slaughter to
prevent dogs access to offal from livestock
Boiling livers and lungs which contain hydatid cysts
for 30 minutes has been proposed as a simple,
efficient and saving way to kill the infectious larvae
15. Terminology
Hydatid : cyst containing watery fluid.
Cyst: a tough protective capsule enclosing the larva of a parasitic worm or the
resting stage of an organism.
Rostella: protruding part at the scolex armed with hooks and used for
attachment with the intestinal wall of the hosts.
Cestode: tapeworm
Protoscolex: The juvenille scolex formed from the germinal layer of a hydated
metacestode
Oncosphere: tapeworm embryo that has six hooks and is the earliest
differentiated stage of a cyclophyllidean tapeworm—called also hexacanth
embryo. OR immature forms of the parasite enclosed in an embryonic
envelope
Cyst morphology: fluid-filled sphere with germinal membrane proliferating
endogenously to form brood capsules
Echinococcus species: E. multilocularis, E. equinus, E. oligarthrus.
Offal means organ meat.
