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HYDATID DISEASE
HYDATID DISEASE
Introduction
Hydatid disease (or echinococcosis) is an uncommon disease that may present with
features of:
●
A space-occupying lesion.
Or rarely:
●
With an anaphylactic type reaction when a cyst suddenly ruptures.
The main issues arising in the ED will relate to:
●
Diagnosis:
♥
●
Resuscitation:
♥
●
The initial diagnosis given the patient’s presenting symptoms, usually
relating to the features of space occupying lesion or as an unsuspected
finding on imaging.
Rarely the resuscitation and management of patient who has presented
because of cyst rupture and allergic reaction.
Disposition:
♥
The planning of the most appropriate disposition.
Treatment of hydatid disease can be very complex and will require close
consultation with infectious disease specialists, surgeons and interventional
radiologists all with experience in treating the disease.
Epidemiology
Hydatid disease occurs worldwide
It is rare in Australia
It is most commonly associated with sheep farming.
Pathology
Organism
●
Echinococcus granulosus (dog tapeworm)
See appendix 1 (below) for the life cycle of Echinococcus granulosus.
Incubation Period
●
The incubation period may vary from months to years.
Reservoir
●
The domestic dog and other canids, definitive hosts for E. granulosus, may
harbour thousands of adult tapeworms without being symptomatic.
●
Felines and most other carnivores are normally not suitable hosts for the parasite.
●
Intermediate hosts include the herbivores, sheep, cattle, goats, pigs, horses,
kangaroos, wallabies and camels.
Sheep are the major intermediate hosts. They eat the worm eggs from pasture
contaminated with dog faeces.
These hatch inside the sheep, forming cysts.
●
The life cycle is completed when dogs are infected through eating the offal of
infected livestock or wild animals, particularly the liver and lung.
Transmission
●
Human infection occurs by hand-to-mouth transfer of tapeworm eggs from dog
faeces.
●
The larvae penetrate the intestinal mucosa, enter the portal system and are carried
to various organs where they produce cysts in which infectious protoscoleces
develop.
●
The important life cycle is dog-sheep-dog.
●
A dingo-wallaby-dingo (or wild dog) sylvatic cycle also occurs.
●
A dog-wild pig-dog cycle has been recognised and poses a special risk for wild
pig-hunters.
Periods of Communicability
●
Hydatid disease is not transmitted from person to person.
●
Dogs pass eggs approximately seven weeks after infection. In the absence of
reinfection this ends within one year.
Susceptibility and Resistance
●
Young children are more likely to be infected as they are more likely to have
closer contact with infected dogs and they are less likely to have appropriate
hygiene habits.
●
There is no evidence however to suggest children are more susceptible to
infection than adults.
Clinical Features
Symptoms will depend on the location of the cyst within the body and develop as a result
of pressure, leakage or rupture or these cysts.
Cyst sites include:
●
Liver, the most common site.
Less commonly:
●
Brain
●
Lungs
●
Kidneys.
Uncommonly:
●
The heart, thyroid and bone may be affected.
Cysts in the body may remain viable or die and calcify.
Sudden rupture of the brood capsules and liberation of the daughter cysts may
cause allergic reactions - even fatal anaphylaxis.
The prognosis however is generally good and will largely depend on the site and potential
for rupture and spread.
Note that persons who have a calcified cyst detected on X-ray may still have active
infection.
Investigations
Diagnosis is often initially made by imaging including plain X-ray, ultrasound or CT
scan.
Plain radiology
Calcified lesions may be seen on plain radiography of the chest or abdomen.
Ultrasound
This may demonstrate hydatid lesions within the liver.
CT scan
Spectacular CT scan images of a 22 year old male Afghani migrant who had fallen onto
his right flank. He presented with RUQ pain, but also had a generalized urticarial rash
dating from the time of his injury. He subsequently developed hypotension. FAST scan
suggested a small amount of free fluid in the pelvis. The subsequent CT scan confirmed
the diagnosis of hepatic hydatid cyst and the report read, “The endocyst is almost
certainly ruptured with detachment of the endocyst from the pericyst, giving a deflated
appearance. The pericyst is also likely ruptured with the overall shape of the cyst having
a deflated appearance. This represents a direct rupture into the peritoneal space”.
Histological examination confirmed the diagnosis of viable hydatid cyst. Hypotension
was due to an allergic reaction due to the release of the cyst contents into the peritoneal
cavity, a well recognized complication of cyst rupture. (CT scan images courtesy Dr
Simon Bolch).
Microscopy
●
If a cyst ruptures, appropriate examination for protoscoleces, brood capsules and
cyst wall in sputum, vomitus, faeces or faeces or urine should be undertaken.
Serology
●
The traditional Casoni skin test has now been replaced by serological tests for
hydatid disease.
These include fluorescent antibody (FA) and indirect haemagglutination antibody
testing.
Management
The main issues arising in the ED will relate to:
●
Diagnosis:
♥
●
Resuscitation:
♥
●
The initial diagnosis given the patient’s presenting symptoms, usually
relating to the features of space occupying lesion or as an unsuspected
finding on imaging.
Rarely the resuscitation and management of the patient who has presented
because of cyst rupture and allergic reaction.
Disposition:
♥
The planning of the most appropriate disposition.
In general terms:
1.
Anaphylactic reactions:
●
2.
Surgery 3
●
3.
These are managed along conventional lines for anaphylaxis.
For symptomatic disease, surgery is often the treatment of choice for
infection with Echinococcus granulosus, especially hepatic cysts,
sometimes combined with prolonged high-dose albendazole 3
Percutaneous drainage 3
●
Percutaneous drainage with ultrasound guidance plus prolonged high-dose
albendazole has been effective for liver cysts.
Percutaneous aspiration, introduction of a protoscolicidal agent (eg
hypertonic saline or ethanol), with re-aspiration after at least 15 minutes
(the PAIR procedure, ie percutaneous aspiration, scolicidal agent infused
and then re-aspirated) is used in selected patients.
Praziquantel followed by prolonged high-dose albendazole is used if there
is cyst spillage from trauma or surgery. Praziquantel may also be used
with albendazole before surgery.
4.
Albendazole 3
●
Small pulmonary lesions may respond to medical treatment alone.
●
Patients on prolonged albendazole therapy require regular monitoring of
liver function tests and white cell count.
●
Treatment of asymptomatic infection is usually not required. 3
Preventive Measures:
●
Basic hygiene such as washing hands with soap after gardening or touching the
dog and washing vegetables that may have been contaminated by dog faeces, are
important in prevention of this disease.
Notification:
●
Not required
School exclusion:
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Not required.
Disposition:
If hydatid disease is suspected, treatment should be discussed with:
●
The infectious diseases Unit
●
A general surgical unit, experienced in the treatment of hydatid disease
●
Interventional radiologist, experienced in the treatment of hydatid disease
Appendix 1
Life Cycle of Echinococcus granulosus:
Hydatid life cycle, (CDC Website, February 2007)
The adult Echinococcus granulosus (3 to 6 mm long) (1) resides in the small bowel of the
definitive hosts, dogs or other canids.
Gravid proglottids release eggs (2) that are passed in the feces.
After ingestion by a suitable intermediate host (under natural conditions: sheep, goat,
swine, cattle, horses, camel), the egg hatches in the small bowel and releases an
oncosphere (3) that penetrates the intestinal wall and migrates through the circulatory
system into various organs, especially the liver and lungs.
In these organs, the oncosphere develops into a cyst (4) that enlarges gradually,
producing protoscolices and daughter cysts that fill the cyst interior.
The definitive host becomes infected by ingesting the cyst-containing organs of the
infected intermediate host.
After ingestion, the protoscolices (5) evaginate, attach to the intestinal mucosa (6), and
develop into adult stages (1) in 32 to 80 days.
The same life cycle occurs with E. multilocularis (1.2 to 3.7 mm), with the following
differences: the definitive hosts are foxes, and to a lesser extent dogs, cats, coyotes and
wolves; the intermediate host are small rodents; and larval growth (in the liver) remains
indefinitely in the proliferative stage, resulting in invasion of the surrounding tissues.
With E. vogeli (up to 5.6 mm long), the definitive hosts are bush dogs and dogs; the
intermediate hosts are rodents; and the larval stage (in the liver, lungs and other organs)
develops both externally and internally, resulting in multiple vesicles. E. oligarthrus (up
to 2.9 mm long) has a life cycle that involves wild felids as definitive hosts and rodents as
intermediate hosts.
Humans become infected by ingesting eggs (2), with resulting release of oncospheres (3)
in the intestine and the development of cysts (4), in various organs.
Hydatid disease in humans is produced by cysts that are the larval stages of the
tapeworm Echinococcus. Brood capsules are formed within cysts, containing 30-40
protoscoleces. Each of these is capable of developing into a single tapeworm.
References
1.
The Blue Book Website.
2.
CDC Website.
3.
Antibiotic Therapeutic Guidelines 14th ed, 2010.