Practice Essentials
Practice Essentials
Cystic Echincococcosis (CE) is an infection caused by the metacestode of the taenia Echinococcus granulosus. [1, 2]
The infection causes the formation of Echinococcal or Hydatid cysts in intermediate hosts. Humans are accidental intermediate hosts. The infection disproportionally affects patients in rural, pastoral communities where sheep rearing is practiced.
The main organs affected by CE are the liver (70-75% of cases), [3] followed by the lungs (10-20% of cases), [4] but any organ can be affected.
Sings and Symptoms
Most cysts (around 70%) stay asymptomatic until found accidentally. Symptomatic cases have features dependent on the size, location and relationship with other organs.
Abdominal CE Patients may present with pain, acute abdomen, jaundice or in very rare instances, features of anaphylactic shock in cases complicated by cyst rupture. Fever due to cyst superinfection may be present, as well as ascites due to portal hypertension. Discharge of cyst membrans or vescicles with urine has been reported in complicated kidney cysts. [5]
Thoracic CE In the case of parenchymal CE, patients usually become symptomatic when a bronchial fistula is present and vomica (i.e. coughing up pieces of cyst membranes or vescicles) occurs. Superinfection and abscess formation has also been reported.
Other localizations Bone CE often presents with pain and neurological symptoms including sensitive or motor deficits and neurological bladder in the most advanced cases. Heart CE can present with embolization. Brain CE can present with seizures or neurological deficit.
Diagnosis
The mainstay of diagnosis for abdominal CE is ultrasound (US), as this technique allows for the use of a WHO-Informal Working Group on Echinococcosis (IWGE) classification for cyst staging. If US expertise is lacking, Magnetic Resonance Imaging (MRI) has been shown to better show stage specific characteristics in patients with liver CE. It is also the imaging method of choice for abdominal cysts not seen by US and for extra-hepatic localizations. CT is still useful for the pre-surgical study of thoracic and liver CE.
Serological assays are available but should not be used as screening tests due to issues with sensitivity in both early and inactive cysts, as well as with issues in cross-reactivity.
Currently, our group endorses the use of at least two first line tests, preferably including an immunoblot. A positive serological case is defined by the positivity of two tests. In one single center experience, western blot had sufficient sensitivity and specificity alone, but an assessment of several serological tests have found variability between different commercial tests. Serology should not be used in the abscence of lesions without imaging characteristics suggestive of CE (eg, isolated hypereosinophilia).
Treatment
Abdominal CE
Non-complicated liver CE can be managed through a stage-specific approach as per WHO-IWGE recommendations: current expert recommendations use cyst stage to direct towards four options (medical treatment, surgery, percutaneous treatments, watch and wait) (see Management for further details). Complicated liver CE is usually managed surgically, with the potential exception of superinfected cysts with abscess formation. In such cases, percutaneous aspiration can be considered. Extra-hepatic cysts and peritoneal localizations require individualized management toghether with an expert provider.
Thoracic CE Lung CE cyst have been shown to respond to medical treatment with benzimidazoles, provided that they are of small dimensions (< 5 cm in diameter). Other cysts require an individualized approach to establish indication for surgerey (e.g. small, inactive cysts may be managed by watch and wait in selected cases), but surgery is the main treatment approach.
Other localizations Other localization of CE require management in conjunction with an expert provider.
SeeTreatment for further details
Background
Cystic echinococcosis (CE) is the larval cystic stage (called echinococcal cysts) of a small taeniid-type tapeworm (Echinococcus granulosus) that may cause illness in intermediate hosts, generally herbivorous animals and people who are infected accidentally. [6] Ultrasonographic (US) appearance of echinococcal cysts is seen in the image below. [7]
WHO Informal Working Group on Echinococcosis standardized ultrasound classification of echinococcal cysts and treatment options.
Three other species are recognized within the genus Echinococcus, and they may also develop in the human host and cause various forms of echinococcosis (hydatidosis). E granulosus is discussed separately from the other 3 species, notably Echinococcus multilocularis, which causes alveolar echinococcosis, because of marked differences in epidemiology, clinical features, diagnosis, and treatment. [8]
In the normal life cycle of Echinococcus species, adult tapeworms (3-6 mm long) inhabit the small intestine of carnivorous definitive hosts, such as dogs, coyotes, or wolves, and echinococcal cyst stages occur in herbivorous intermediate hosts, such as sheep, cattle, and goats. [6, 9, 10] A number of other suitable intermediate hosts, such as camels, pigs, and horses, are involved in the life cycle in many parts of the world. [6, 9, 10]
In the typical dog-sheep cycle, tapeworm eggs are passed in the feces of an infected dog and may subsequently be ingested by grazing sheep; they hatch into embryos in the intestine, penetrate the intestinal lining, and are then picked up and carried by blood throughout the body to major filtering organs (mainly liver and/or lungs). After the developing embryos localize in a specific organ or site, they transform and develop into larval echinococcal cysts in which numerous tiny tapeworm heads (called protoscolices) are produced via asexual reproduction. [6, 9, 10]
These protoscolices are infective to dogs that may ingest viscera containing echinococcal cysts (with protoscolices inside), mainly because of the habit in endemic countries of feeding dogs viscera of home-slaughtered sheep or other livestock. [6, 9, 10]
Protoscolices attach to the dog's intestinal lining and, in approximately 40-50 days, grow and develop into mature adult tapeworms, once again capable of producing infective eggs to be passed to the outside environment with the dog's feces.
Because humans play the same role of intermediate hosts in the tapeworm life cycle as sheep, humans also become infected by ingesting tapeworm eggs passed from an infected carnivore. This occurs most frequently when individuals handle or contact infected dogs or other infected carnivores or inadvertently ingest food or drink contaminated with fecal material containing tapeworm eggs. [6, 9, 10]
Pathophysiology
In primary CE, metacestodes develop from oncospheres after peroral infection with E granulosus eggs. In secondary echinococcosis, larval tissue proliferates after being spread from the primary site of the metacestode. This can occur by spontaneous trauma such as induced rupture or during medical interventions.
In primary CE, larval cysts may develop in every organ. [11] Most patients (as many as 80%) have single-organ involvement and harbor a solitary cyst. [9, 10] Approximately two thirds of patients experience liver echinococcosis. [3, 12] The second most common organ involved is the lung. [4, 8]
In each anatomic site, cysts are surrounded by the periparasitic host tissue (pericyst), which encompasses the endocyst of larval origin. Inside the laminated layer, or hyaline membrane, the cyst is covered by a multipotential germinal layer, giving rise to the production of brood capsules and protoscolices. The central cavities of cysts of E granulosus are filled with clear fluid, numerous brood capsules, and protoscolices. In addition, daughter cysts of variable size often are detected. The growth rate of cysts is highly variable and may depend on strain differences. Estimates of the average increase of cyst diameter vary, depending on the target organ and host dependent factors that are not completely studied, although historically a growth of around 1 cm/year has been reported. [13]
The clinical features of cystic echinococcosis are highly variable. The spectrum of symptoms depends on the following:
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Involved organs
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Size of cysts and their sites within the affected organ or organs
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Interaction between the expanding cysts and adjacent organ structures, particularly bile ducts and the vascular system of the liver
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Complications caused by rupture of cysts
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Bacterial infection of cysts and spread of protoscolices and larval material into bile ducts or blood vessels
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Immunologic reactions such as asthma, anaphylaxis, or membranous nephropathy secondary to release of antigenic material [14]
Epidemiology
Unfortunately, realistic national or international figures do not exist for total numbers of cases of CE. This is largely due to the undereporting of cases, due to the lack of official notification systems in many countries. Even countries that do have notification systems often do not collect data on CE.
When they have reported cases, uneven reporting occurred in different regions of countries. Moreover, the groups most at risk for CE are usually underserved by medical services. [10] Recently, epidemiological studies carried out with ultrasound have clarified that the disease is severely underreported. Furthermore, the EuropeanRegistry for Cystic Echinococcosis (ERCE) has gathered a number of cases superior to those present in the ECDC reporting systems for a consistent number of years. [15, 16, 17]
United States
In the United States, transmission of E granulosus in the dog-sheep cycle is known to occur most frequently in several western states, including California, Arizona, New Mexico, and Utah. In Arizona and New Mexico, cystic echinococcosis is known to occur in American Indians belonging to the Zuni, Navajo, and Santo Domingo tribes, whose members live in close proximity to their animals, kill many of their own animals each year, and generally have limited knowledge concerning the life cycle and transmissibility of the parasite. In the United States, Utah has had the highest number of surgical cases of those states involved, with approximately 45 cases from 1944-1994. [18]
International
E granulosus is a cosmopolitan parasite, and endemic regions exist in each continent. Considerable public health problems occur in many areas, including countries of Central America and South America, Western and Southern/Southeastern Europe, the Middle East and North Africa, some sub-Saharan countries, Russia and adjacent countries, and China. Annual incidence rates of diagnosed human cases per 100,000 inhabitants vary widely, from less than 1 case per 100,000 to high levels. For example, rates in the indicated regions are as follows:
Greece - 13 cases per 100,000 persons
Rural regions of Uruguay - 75 cases per 100,000 persons
Rural regions of Argentina - 143 cases per 100,000 persons in Rio Negro province
Parts of Xinjiang province of China - 197 cases per 100,000 persons Parts of the Turkana district of Kenya - 220 cases per 100,000 persons
CE causes not only illness but also productivity losses in human and agricultural animal population, and it can have large societal impacts on endemic areas. Research is ongoing to evaluate the burden of disease, including nonmonetary costs. [18, 19]
Prognosis
Prognosis generally is good but it depends on the cyst location. For instance, neither surgery nor medical therapy is generally effective for bone, especially spinal, CE. Surgery to treat cardiac cysts can be risky, and there is very little experience with the use of albendazole in this site.
Sometimes after removal of a cyst, one or more new cysts may develop at a different site. A hypothesis for this is that the growth of some cysts may be inhibited by the presence of the cyst that has been removed.
Patient Education
Patient education should include the followoing:
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Cystic Echinococcosis (CE) is an infection caused by the tapeworm E granulosus. It causes the formation of hydatid cysts in several organs of the human body.
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The infection is acquired by ingesting food or water contaminated by parasitic eggs present in dog faeces.
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CE can be prevented by correctly washing hands before meals, as well as by properly cooking food.
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Another fundamental action is avoiding the homeslaughtering of ruminants such as goats or sheep as offals are often left for the dogs to consume.
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When acquired, the infection is often asymptomatic (around 70% of cases) and spontaneous cure of CE is possible
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Abdominal CE is best diagnosed by ultrasound, as this allows the clinician to stage the cysts and differentiate between active and inactive CE
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Thoracic CE is more frequently symptomatic than abdominal CE: the presence of vomica (coughing up of cyst membranes) is a typical sign
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However, the treatment of active cysts requires care by an experienced physician, as treatment is not always necessary for abdominal CE and can sometimes be avoided for other, rarer localizations.
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WHO Informal Working Group on Echinococcosis standardized ultrasound classification of echinococcal cysts. Image courtesy of World Health Organization (WHO).
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CE1 cyst in the right segments of the liver in a young Albanian boy
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CE3a echinococcal cyst of the liver. Note the folding endocyst ("waterlily sign") typical of CE3a cysts.
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CE3b cyst in the right lobe of the liver. The cyst is predominantly solid with a few daughter cysts
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CE4 cyst in the liver. The cyst is completely solid and inactive.
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CE3b cyst in the muscles of posterior thigh (scanned with a convex ultrasound probe).
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CE4 cysts in the peritoneum in a patient with disseminated echinococcosis (longitudinal scan).
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Viable scolices (note rostellar hooklets).
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CT scan of peritoneal, disseminated echinococcosis
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MR scan of echinococcal cyst in the right psoas muscle, infiltrating the adjacent vertebral body
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Ultrasound scan of a CE3b subcutaneous cyst located in the lumbar area. The cyst was the subcutaneous extension of a cyst located in the spine that had been previously operated on.
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MR of the spine showing CE involvement of CE3,CE4,CE5 vertebral bodies, spinous processes and subcutaneous tissue (same patient as # )
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CT scan showing CE infiltration of vertebral bodies and destruction of left peduncles
