Microbiology of the Hydatid cysts

1. Hydatid Cysts.
Nirav Hitesh Kumar Valand.

2. Introduction
•Caused by the cestode Echinococcus granulosus.
•Also called unilocular cyst disease.
•Sheep, goats, camels, and horses are among the usual
intermediate hosts for E. granulosus.
•E. granulosus is transmitted by domestic dogs in livestock
raising areas, hydatid disease is prevalent worldwide
(Africa, Middle East, southern Europe, Latin America, and
southwestern United States)

3. Properties of the cestode.
•E. granulosus is composed of a scolex and only three
proglottids :one immature, one mature, and one gravid.
The gravid segment splits to release eggs.
•The scolex has a circle of hooks and four suckers.

5. Life cycle
•The adult form lives in the intestinal tract of carnivorous
animals, such as dogs and wolves.
•Typically, humans become infected from the feces of a dog that
has become infected by eating the flesh of a sheep or deer
containing the cyst form of the tapeworm.
•Humans acquire echinococcosis by ingesting viable parasite
eggs with their food.
•Eggs are partially resistant to desiccation and remain viable for
many weeks, allowing delayed transmission to individuals with
no direct contact with vector animals.

6. •Once in the intestinal tract, the eggs hatch to form
oncospheres that penetrate the mucosa and enter the
circulation.
•Oncospheres then encyst in host viscera, developing over time
to form mature larval cysts i.e. the hydatid cysts.
•the inner germinal layer of the hydatid cyst generates many
protoscoleces.
•The protoscoleces are contained within brood capsules. If the
hydatid cyst ruptures, the brood capsules can spill out of the
cyst, metastasize to other sites, and develop into a hydatid cyst.
•The hydatid cysts of E. granulosus tend to form in the liver (50%
to 70% of patients) or lung (20% to 30%) but may be found in
any organ of the body, including brain, heart, and bones (<10%)

8. Epidemiology.
•These parasites are found on all continents, with
areas of high prevalence in China, central Asia, the
Middle East, the Mediterranean region, eastern
Africa, and parts of South America.

9. Risk factors.
•Unsanitary living conditions.
•Slaughter of livestock in close proximity to humans and
dogs, and uncontrolled dog populations.
•Sheep raising in particular, is associated with a high
prevalence of disease.

10. Pathology and Pathogenesis
•Hydatid cysts can grow about 1–7 cm per year, and the
symptoms depend on the location of the cysts in the body.
•The liver is the most common site, where compression,
atrophy, portal hypertension from mechanical obstruction, and
cirrhosis can occur.
•Extreme care must be taken when removing the cyst. If the cyst
ruptures, the highly immunogenic hydatid fluid can lead to
anaphylactic shock and brood capsules can metastasize to form
additional hydatid cysts.

11. Clinical features.
•The slowly growing Echinococcus usually has an asymptomatic
stage, unless it is large enough to cause space occupying
effects.
•There maybe abdominal pain or an enlargement in the right
upper quadrant.
•Compression of a bile duct or leakage of cyst fluid into the
biliary tree may mimic recurrent cholelithiasis, and biliary
obstruction can result in jaundice.
•Rupture of or episodic leakage from a hydatid cyst may
produce fever, pruritus, urticaria, eosinophilia, or anaphylaxis

12. •Pulmonary hydatid cysts may rupture into the bronchial tree or
peritoneal cavity and produce cough, dyspnea, chest pain, or
hemoptysis.
•Other presentations are due to the involvement of
• bone (invasion of the medullary cavity with slow bone erosion
producing pathologic fractures),
• CNS (space-occupying lesions),
• Heart (conduction defects, pericarditis),
• Pelvis (pelvic mass).

13. Diagnosis.
•Chest X-ray that demonstrates pulmonary lesions as slightly
irregular, round masses of uniform density, often devoid of
calcification. In contrast, more than one-half of hepatic lesions
display a smooth, calcific rim.
•ELISA.
•A specific diagnosis of E. granulosus infection can be made by
the examination of aspirated fluids for protoscoleces or
hooklets, but diagnostic aspiration is not usually recommended
because of the risk of fluid leakage resulting in either
dissemination of infection or anaphylactic reactions.

14. TREATMENT.
•Definitive treatment is surgical excision of the cysts in toto. A
protoscolicidal agent (e.g., hypertonic saline) should be
injected into the cyst to kill the organisms and prevent
accidental dissemination.
•For uncomplicated lesions, Percutaneous Aspiration, Infusion of
scolicide and Reaspiration (PAIR) can be used in lieu of surgery.
•It is recommended that high-dose albendazole be administered
before and for several weeks after surgery and/or aspiration.

15. Prevention
• Infected dogs should be dewormed, and infected
carcasses and offal burned or buried.
• Hands should be carefully washed after contact with
potentially infected dogs.