Hydatid cyst is caused by the larval stage of Echinococcus granulosus ( cestode tape worm)
Cosmopolitan in distribution , more common in sheep& cattle raising countries.
Morphology& life cycle:
The adult worm is minute 3-6mm in small intestine of dogs& other carnivores.
The scolex is pyriform , provided with four suckers & armed with 30-40
hooks, followed by the neck & body segments ( immature, mature& gravid segment )
.The adult is attached to the mucosa of the small intestine of dogs& other canines&
lives for 5-29 months..
The eggs pass with faeces of dogs . The eggs cannot be distinguished from those of
Taenia species in dogs. When the eggs are swallowed by herbivores animals
such as sheep , cattle & accidentally man; they hatch in the duodenum &
onchosphere migrate through the intestinal wall, enter the mesenteric venules &
become lodged in various organs
In these organs the larvae begin to develop into a cystic structure called hydatid
The life cycle comes to a dead end in case of human infection .
Most patients have single organ involvement & harbour solitary cyst.
Approximately two thirds of patients experience liver hydatid cyst & the second
most common organ involved is the lung.
It is usually a classical unilocular cyst which grows slowly & its size varies from a pin,s head to a child,s head.
The cyst is surrounded by a layer of fibrous tissue made by the host as a result of immunological response. .
The cyst wall proper consist of two layers , outer non- nucleated laminated layer & inner nucleated germinal layer .
From the inner layer brood capsules & daughter cysts develop. Inside the brood capsules are the protoscolices which when fully mature are infective .
Inside the cyst there is hydatid fluid which secreted by the germinal layer to provide nourishment for the developing scolices, it is antigenic & highly toxic
The free broad capsules& protoscolices are called hydatid sand.
leakage of the fluid in the body will give rise to anaphylactic shock.
Dogs & other carnivores are infected when they eat the hydatid cyst containing scolices where by each scolex develop into adult worm .
The clinical features of HC are highly variable. The spectrum of symptoms depend
on the following:
Size of the cyst & their sites within the affected organ
Interaction between expanding cysts& adjacent organ structures
Complication caused by the rupture of the cyst
Bacterial infection of the cyst& spread of portoscolices
Immunological reactions such as asthma, anaphylaxis secondary to release of antigenic material
Hydatid cyst in the lung
When man ingest the eggs of the E. granulosous , they hatch in the intestine & the
Liberated onchosphere migrate through the intestinal wall , inter mesenteric venules &
Become lodged in various organs including the lung .
Pathogenesis & clinical picture
The damage produced by the hydatid cyst is mainly mechanical , thus the cyst lodged in the lung may interfere with lung functions. Cough , dyspnoea & haemoptysis may occur .
Allergic manifestations due to escape of hydatid fluid can occur .
Rupture of the cyst may produces anaphylactic shock & dissemination of scolices into the circulation to become lodged in other organs where they produce dangerous effects
During the natural course of infection, the fate of the cyst is variable:
Usually the cyst does not induce clinical symptoms before they have reached a size sufficient to exert pressure on adjacent organ.
Some cysts may grow to a certain size & then persist without noticeable change for many years
Other may rupture spontaneously or collapse & completely disappear.
Spontaneous cure may possible
Spontaneous or traumatic rupture & spillage of variable parasitic tissues during surgical intervention may result in secondary HC.
Hydatid cyst should be considered in patients with mass in the lung particularly in the
base of the Lung.
X- ray examination, ultrasound are highly effective in locating the cyst but do not establish the diagnosis .
Ultrasound is the procedure of choice when making the diagnosis of asymptomatic infection because it is safe, non- invasive & relatively inexpensive
2- Hydatid thrill.
3- Eosinophilia is present in 20- 25 % of the cases .
4- Cyst puncture can be fatal owing to the possibility of metastasis or leakage of fluid
that may lead to anaphylactic shock . A technique of freezing a cyst wall for safe
aspiration has been described .
5-Immunological diagnosis by :
IHA- ELISA –CFT
6-Casoni test : intradermal casoni's but it is not sensitive .
Albendazole & mebendazole are the only two drugs effective against HC.
Albendazole is significantly effective than mebendazole due to its high degree of systemic absorption & penetration into the cysts is superior to mebendazole.
The patient receive 400mg/kg twice daily for 4 weeks & repeated after 2 weeks for 3 cycles.
Praziquantel has recently been suggested , administered additionally once per week in 40mg/kg during treatment with albendazole
Surgical removal is usually recommended in accessible sites( albendazole may be given prior to operation ).
The risk of surgery include; leakage of fluid which could give rise to:
B- Metastatic cyst formation.
Minimal invasive procedure under albendazole coverage, cysts are punctured &injected with scolicidal agent , usually hypertonic sodium chloride solution or ethanol& leave for a period of 5-30 min & then re-aspirated . This procedure is termed PAIR( puncture, aspiration, injection & re-aspiration). This procedure is used as diagnostic & treatment for hydatid cyst
Strict personal hygiene , since the parasite is transmitted through intimate contact with dogs or from dog's faeces .
Dogs should be prevented from eating carcasses of slaughtered animals & treatment of infected dogs by praziquantel.
Life cycle & morphology of echinococcus granulosus
Adult worm of E. granulosus
Structure of hydatid cyst
Paragonimus westermani is a trematode parasite living in the lungs of human beings & carnivores.
In far east heavily infected areas are found including Japan., Korea& Tiwan.
The adult worm is ovoidal in shape, its size about7.5-12mm, rounded anteriorly& tapering posteriorly.
The cuticle is covered with spines. The oral & ventral suckers are unequal.
The intestinal ceaca are simple extending to the posterior end of the worm.
The two testes are lobed, mid way between the ventral sucker& post. End.
The uterus is rosette shaped & lies opposite the ovary
Ovoidal with flattened operculum, golden brown in colour.
The eggs escape from the pulmonary pockets through the bronchioles&
are coughed out with the sputum or swallowed& passed in faeces immature
Life cycle & mode of infection
- The worm passes its life cycle in three hosts:
One definitive : man & domestic animals
Two intermediate hosts : first fresh water snail of genus Melania
Second host fresh water Cray fish & crabs.
The eggs require 15 days to several weeks in water for maturation. The eggs hatch& miracidia are escaped& enter the snail intermediate host .
Inside the snail , the miracidia develop into sporocyst, redia, cercaria in three to five months.(13weeks)
The released cercaria penetrate the crabs or Cray fish & develop into metacercariae in the gills, muscles , legs or viscera of crustaceans. Metacercariae require 6-8 weeks to become infective.
Human infection occurs when eating crabs or Cray fish raw or under cooked containing the metacercariae.
The metacercariae excyst in intestine, penetrating the intestinal wall& grow for about a week into young flukes then migrate to the lung. It takes 6-8 months to complete the life cycle.
Mode of infection
Infection is occurred by eating infected fresh- water crabs & Cray fish.
It is customary in the orient to consume these uncooked crustaceans in brine, vinegar or wine as "drunken crabs" in which metacercarisae may survived for several hours.
Crushed crabs juice, taken orally & used in treatment of measles in Korea, may be a source of infection in children.
Metacercariae are killed if crabs are roasted until muscle turn white or if they are heated in water 55c for 5 minutes.
When the worm settle in ectopic foci, the provoke a granulomatous reaction which lead to fibrotic encapsulation.
In the lungs the flukes provoke leucocytic infiltration with development of cystic encapsulation of the parasite.
The cysts contain a purulent fluid with brownish discolouration due to the presence of eggs & are surrounded by fibrous tissue capsule.
There is a picture of localised diffuse fibrosis, pneumonia& tubercle like abscesses. In addition to lung, cysts may be found in the liver ,intestinal wall…ect
Clinically the disease is insidious in its onset. There may be an initial episode of chills, fever with accompanying dry cough at first
Later on the cough may be productive with rusty brown sputum most prounced on raising in morning.
Pulmonary pain & pleurisy may be present
Finding the characteristic eggs in sputum, aspirated pleural effusion or faeces in heavily infected patients.
Serological diagnosis such as :
ELISA& western blot
Complement fixation to evaluate the severity of the disease
Eosinophilia is constant finding in all cases.
Praziquantel 25 mg /kg b.wt for 3 days.
Prevention & control
Abstaining from eating raw or inadequately cooked crabs or Cray fish.
Life cycle of paragonimus westermani