Version May 2024
INTRODUCTION — Echinococcal disease is caused by infection with the metacestode stage of the tapeworm Echinococcus, which belongs to the family Taeniidae. Four species of Echinococcus produce infection in humans; E. granulosus and E. multilocularis are the most common, causing cystic echinococcosis (CE) and alveolar echinococcosis (AE), respectively. The two other species, E. vogeli and E. oligarthrus, cause polycystic echinococcosis but have only rarely been associated with human infection [1].
The clinical manifestations and diagnosis of CE and AE infection will be reviewed here. The epidemiology, treatment, and prevention of echinococcosis are discussed separately. (See "Epidemiology and control of echinococcosis" and "Echinococcosis: Treatment".)
CYSTIC ECHINOCOCCOSIS (E. GRANULOSUS)
Clinical manifestations
Signs and symptoms — The initial phase of primary infection is always asymptomatic. Many infections are acquired in childhood but do not cause clinical manifestations until adulthood. Latent periods of more than 50 years before symptoms arise have been reported. While approximately 50 percent of detected cases occur in asymptomatic patients, many more cases remain undiagnosed or are found incidentally at autopsy.
The clinical presentation of E. granulosus infection depends upon the site of the cysts and their size. Small and/or calcified cysts may remain asymptomatic indefinitely. However, symptoms due to mass effect within organs, obstruction of blood or lymphatic flow, or complications such as rupture or secondary bacterial infections can result.
Cysts typically increase in diameter at a rate of one to five centimeters per year. However, cyst growth rates and time courses are highly variable [2,3]. Hydatid cysts may be found in almost any site of the body, either from primary inoculation or via secondary spread. The liver is affected in approximately two-thirds of patients, the lungs in approximately 25 percent, and other organs including the brain, muscle, kidneys, bone, heart, and pancreas in a small proportion of patients. Single-organ involvement occurs in 85 to 90 percent of patients with E. granulosus infection, and only one cyst is observed in more than 70 percent of cases (image 1).
Liver involvement — E. granulosus infection of the liver frequently produces no symptoms. The right lobe is affected in 60 to 85 percent of cases. Significant symptoms are unusual before the cyst has reached at least 10 cm in diameter. If the cysts become large, hepatomegaly with or without associated right upper quadrant pain, nausea, and vomiting can result (picture 1).
In approximately one-fourth of the cases, E. granulosus cysts rupture into the biliary tree, producing biliary colic, obstructive jaundice, cholangitis, and/or pancreatitis [4,5]. Less commonly, cysts rupture into the peritoneal cavity or other organs, with potential for anaphylaxis and multiorgan failure.
Pressure or mass effect on the bile ducts, portal and hepatic veins, or the inferior vena cava can result in cholestasis, portal hypertension, venous obstruction, or Budd-Chiari syndrome. (See "Etiology of the Budd-Chiari syndrome".)
Liver cysts can also rupture into the peritoneum, causing peritonitis, or transdiaphragmatically into the pleural space or bronchial tree, causing pulmonary hydatidosis or a bronchial fistula. Secondary bacterial infection of the cysts can result in liver abscesses. (See "Pyogenic liver abscess".)
Lung involvement — The most common symptoms of pulmonary cystic echinococcosis (CE) described in the literature include cough (53 to 62 percent), chest pain (49 to 91 percent), dyspnea (10 to 70 percent), and hemoptysis (12 to 21 percent). Less frequent symptoms include malaise, nausea and vomiting, and thoracic deformations [6,7]. The majority of children and adolescents with lung lesions are asymptomatic despite having lesions of impressive size, assumedly because of a weaker immune response and the relatively higher elasticity of the lung parenchyma relative to older patients [6,8].
Cysts can break or develop secondary bacterial infection. The presence of these complications changes the clinical presentation, either by causing new symptoms or by increasing the severity of existing symptoms. The principal complication is cyst rupture, with spilling of cyst material containing fragments of larval tissue and protoscolices into the bronchial tree or the pleural cavity. Bronchial tree involvement can lead to cough, chest pain, hemoptysis, or emesis; pleural cavity involvement can cause pneumothorax, pleural effusion, or empyema. Secondary bacterial infection of the cyst can manifest as a pulmonary abscess with poorly defined margins [9-11].
Approximately 60 percent of pulmonary hydatid disease affects the right lung, and 50 to 60 percent of cases involve the lower lobes [12]. Multiple cysts are common. Approximately 20 percent of patients with lung cysts also have liver cysts [13]. The ratio of lung to liver involvement is higher in children than in adults [13].
Other organs — Involvement of organs outside of the liver or lung is unusual but can lead to significant morbidity and mortality.
●Infection of the heart can result in mechanical rupture with widespread dissemination or pericardial tamponade [14-16].
●Central nervous system involvement can lead to seizures or signs of raised intracranial pressure; infection of the spinal cord can result in spinal cord compression [17].
●Cysts in the kidney can cause hematuria or flank pain [18]. Immune complex-mediated disease, glomerulonephritis leading to the nephrotic syndrome, and secondary amyloidosis have also been described [19,20].
●Bone cysts are usually asymptomatic until a pathologic fracture develops; growth of the parasite in the bone tissue is a very slow process; the spine, pelvis, and long bones are most frequently affected [21,22].
●Ocular cysts also occur [23,24].
●Subcutaneous cyst has been described [25,26].
Cyst rupture — Fever and acute hypersensitivity reactions, including anaphylaxis, may be the principal manifestations of cyst rupture. Hypersensitivity reactions are related to the release of antigenic material and secondary immunologic reactions. (See "Anaphylaxis: Emergency treatment".)
Laboratory findings — Nonspecific leukopenia or thrombocytopenia, mild eosinophilia, and nonspecific liver function abnormalities may be observed but are not diagnostic. Eosinophilia is observed in fewer than 15 percent of cases and generally occurs only if there is leakage of antigenic material.
Diagnosis — The diagnosis of E. granulosus is generally made by imaging techniques in conjunction with serology.
For asymptomatic individuals in endemic areas, screening with imaging and serology has been found useful in epidemiologic studies [27]; outside of endemic areas, the role of screening for asymptomatic individuals is uncertain [28].
Imaging — Hydatid cysts may be visualized and evaluated with ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI). Ultrasonography is employed most widely because it is easy to perform and relatively inexpensive. Portable ultrasound machines are frequently used for screening patients in communities in which E. granulosus infection is endemic, sometimes with confirmatory serologic testing to maximize the diagnostic yield [29]. However, CT or MRI may be useful for circumstances in which greater anatomic detail is needed to establish the location and number of cysts, the presence or absence of daughter cysts, and presence of ruptured or calcified cysts, which are important for guiding management (table 1).
Plain radiography may demonstrate calcification within a cyst but cannot detect uncalcified cysts so is not adequate for definitive diagnostic evaluation.
Ultrasonography — The sensitivity of ultrasonography for evaluation of Echinococcus is 90 to 95 percent [30,31]. The most common appearance on ultrasound is an anechoic, smooth, round cyst, which can be difficult to distinguish from a benign cyst. In the presence of liver cyst membranes, mixed echoes can be confused with an abscess or neoplasm. In the presence of daughter cysts, characteristic internal septation can be seen.
Shifting the patient's position during ultrasonography may demonstrate "hydatid sand," which consists predominantly of hooklets and scolexes from the protoscolices. Hydatid disease is probable in the setting of hydatid sand, inner cyst wall infoldings, and separation of the hydatid membrane from the wall of the cyst observed on ultrasound [32].
Ultrasound allows classification of the cyst(s) as active, transitional, or inactive based on biologic activity; such categorizations may influence the choice of treatment (image 2). Characteristics suggestive of an inactive lesion include a collapsing, flattened elliptical cyst (corresponds to low pressure within the cyst), detachment of the germinal layer from the cyst wall ("water lily sign"), coarse echoes within the cyst, and cyst wall calcification [33,34]. Cysts with a calcified rim may have an "eggshell" appearance.
Several other classification systems are based upon ultrasound appearance (image 2):
●The World Health Organization (WHO) classification characterizes cysts by type and size (table 1) [27].
●The Gharbi classification divides cysts into five types [35]. Type I cysts consist of pure fluid; type II have a fluid collection with a split wall; type III cysts contain daughter cysts (with or without degenerated solid material); type IV have a heterogeneous echo pattern; and type V have a calcified wall [35].
WHO categories CE1 and CE2 are active cysts. Type CE1 is unilocular, and type CE2 is multilocular with daughter cysts (figure 1). Class CE3 consists of cysts that are thought to be degenerating (transitional group). There are two types of CE3: CE3a, featuring the "water-lily" sign for floating membranes, and CE3b, which is predominantly solid with daughter cysts. Establishing whether daughter cysts are present is important for guiding treatment. In addition, nuclear magnetic resonance has demonstrated that CE3a and CE3b have different metabolic characteristics [36]. Classes CE4 and CE5 are considered inactive. By ultrasonography, they are echogenic with increasing degrees of calcification and are nearly always nonviable.
It is important to establish whether daughter cysts (cysts that have involuted from the wall and reside within the larger cyst) are present and to distinguish them from brood capsules, which are attached to the wall of the larger cyst. This distinction is important for guiding treatment.
Lung cysts may be single or multiple, usually do not calcify, rarely lead to daughter cyst formation, and may contain air if the cyst has ruptured.
Computed tomography — Many reports suggest that CT has higher overall sensitivity than ultrasonography (95 to 100 percent) [30,31,37]. CT is the best mode for determining the number, size, and anatomic location of the cysts and is better than ultrasound for detection of extrahepatic cysts. CT may also be used for monitoring lesions during therapy and to detect recurrences (image 1) [38].
CT may be superior to ultrasonography in assessing for complications such as infection and intrabiliary rupture [39]. In one study, ultrasound performed better than CT in the investigation of the cyst wall, hydatid sand, daughter cysts, and splitting of the cyst wall, while CT was superior for detecting gas and minute calcifications within the cysts, in attenuation measurement, and in anatomic mapping [34,40].
Magnetic resonance imaging — MRI has no major advantage over CT for evaluation of abdominal or pulmonary hydatid cysts, except in defining changes in the intra- and extrahepatic venous system [41]. MRI may delineate the cyst capsule better than CT and may be better at diagnosing complications, particularly for cysts with infection or biliary communication. However, MRI is usually not required and, in most instances, is not cost effective [42-44].
Both CT and MRI are useful in diagnosing echinococcal infection in other sites such as in the brain [45].
Laboratory tools — Serology is useful for primary diagnosis and for follow-up after treatment [46-48]. Antibody detection is more sensitive than antigen detection for diagnosis of E. granulosus [46].
Serologic tests — Diagnostic serologic techniques include:
●Complement fixation
●Indirect hemagglutination (IHA)
●Indirect immunofluorescence
●Latex agglutination
●Double diffusion immunoelectrophoresis
●Counter-current immunoelectrophoresis
●Radioimmunoassay
●Enzyme-linked immunosorbent assay (ELISA)
●Enzyme-linked immunoelectrodiffusion assay (ELIEDA)
●Time-resolved fluoroimmunoassay
●Immunoblot
The sensitivity and specificity of a number of the serologic tests have been compared (table 2). ELISA appears to be the most sensitive and specific of the available assays [49-54]:
●One study of 79 patients with surgically confirmed pulmonary hydatidosis demonstrated that immunoglobulin (Ig)G ELISA was the most sensitive (84 percent), followed by IgM ELISA (62 percent), passive hemagglutination (61 percent), latex agglutination (58 percent), immunoelectrophoresis (51 percent), and specific IgE ELISA (44 percent). The specificity of all tests was 98 to 100 percent. Specific IgG ELISA had the highest negative predictive value (93 percent) [49].
●One study compared eight serologic tests among 131 patients with E. granulosus infection [52]. IgG ELISA was the most sensitive (94 percent) and specific (99 percent) for the majority of cyst locations.
●One report compared six different serologic tests for the diagnosis of cystic hydatid disease among 243 patients with surgically confirmed infection [53]. The two ELISA tests gave identical results, with a sensitivity of 89 percent for liver cysts and 78 percent for lung cysts. In the 39 patients with false-negative results, the use of immunoblotting only increased the yield by 8 percent; ELIEDA did not identify any additional cases.
The methods most frequently employed for initial screening tests (using crude antigens such as hydatid fluid or protoscolex extracts) are ELISA and IHA. Confirmatory tests using specific antigens can then be performed, such as immunoelectrophoresis and immunoblotting [51]. Additional tests using recombinant or purified species-specific antigens may also be useful diagnosis [55].
Simple, heat-stable, inexpensive tests, such as hydatid antigen dot immunoassays, are often used for field testing and population screening [56]. The dot-ELISA has a reported sensitivity of 88 to 96 percent and a specificity of 90 to 98 percent [57-59].
Two major E. granulosus antigens utilized in serologic testing include antigen 5 and antigen B:
●Antigen 5 is a major parasite antigen found on the inner aspect of the germinal layer, brood capsule, and protoscolices. Only a few studies have assessed the value of tests based on recombinant antigen 5, which has relatively low specificity, although it is used quite extensively for diagnosis in clinical practice [51].
●Antigen B is a highly immunogenic polymeric lipoprotein. Studies have showed that antigen B shows a high degree of genetic variability [60]. It offers greater specificity than detection of antigen 5; however, neither antigen is specific for E. granulosus per se despite a very high specificity for echinococcal infection [61,62].
The sensitivity of these antigens in ELISA assays is 60 to 90 percent and the specificity is usually approximately 90 percent [63]. The sensitivity in immunoblot and gel diffusion assays is approximately 90 percent with a specificity of 97 to 100 percent [62,64]. One study demonstrated that the immunoblot with the antigen B–rich fraction was positive in 92 percent of patients with E. granulosus but was also positive in 79 percent of patients with E. multilocularis [65]. No cross-reactivity was observed with sera from patients with other parasitic diseases, malignancies, or healthy controls.
A variety of issues influence the rates of false-positive and false-negative serologic results. First, there is a lack of standardization among different laboratories; for example, one study showed that ELISA using antigen B had a sensitivity of 63 percent, whereas immunoblotting using the same antigen had a sensitivity of 80 percent [66]. Second, methods of antigen isolation and purification can influence the results. Third, serological assays with high sensitivity and specificity for diagnosis of cystic echinococcosis in clinical settings can be less useful in epidemiological studies; these assays may detect only half of liver cysts in field surveys and as few as 20 percent of lung cysts [67,68].
The utility of serology can be improved by using a combination of tests or sequential testing [69]. Tests employing a number of recombinant antigens are being evaluated to improve the sensitivity and specificity of the commercially available serologic tests. A highly sensitive assay, usually an ELISA or indirect hemagglutination test, is commonly used as an initial screen, followed by a highly specific immunoblot or gel diffusion assay for confirmation. Testing for specific antibodies, such as specific IgG1 or IgG4 rather than total IgG, may improve specificity [66,70-72].
●Interpreting negative test results − A negative serologic test generally does not rule out echinococcosis. There is no consistent correlation between serologic results and the number or size of cysts [49]. In general, liver cysts elicit an antibody response more frequently than lung cysts. Overall, approximately 85 to 95 percent of liver cysts and 65 percent of lung cysts are associated with positive serology, although this varies with the specific serologic test used and cyst activity [50]. Brain, eye, and splenic cysts often do not produce detectable antibodies, whereas bone cysts frequently are associated with positive serology. Serology is less likely to be positive with cysts at any site if the cysts are intact, calcified, or nonviable.
The likelihood of false-negative results is variable depending on the site of the lesion and the integrity and viability of the cyst. Antigen-antibody complexes that "mop up" all antibodies may lead to false-negative reactions. The sensitivity of serologic assays is often assessed in human patients whose cysts are not intact, leading to high rates of positive serology [73]. The sensitivity of the same assays are much lower in human cases detected as part of epidemiologic studies (eg, ultrasound surveys) [3,67]. False-positive reactions are more likely in the presence of other helminth infections (such as Taenia saginata, Taenia solium, and particularly neurocysticercosis), cancer, and immune disorders.
Antigen assays — A variety of purified or recombinant diagnostic antigens have been evaluated. Demonstration of antigens in cystic fluid or serum can also be used for diagnosis of primary infection or relapse [69,74,75]. However, up to 50 percent of patients with echinococcal cysts do not have circulating antigens. Latex agglutination or a dot-ELISA to detect echinococcal antigens from cyst fluid have excellent sensitivity and specificity [76-78]. Antigen assays and tests for circulating immune complexes are not widely available but may become useful tests in the future [79].
Polymerase chain reaction — Polymerase chain reaction techniques are limited to research settings but may play a diagnostic role in the future [80]. Deoxyribonucleic acid (DNA) probes using Southern hybridization tests are also being developed [81].
Interventional procedures
Cyst aspiration or biopsy — In the absence of a positive serologic test, percutaneous aspiration or biopsy may be required to confirm the diagnosis by demonstrating the presence of protoscolices, hooklets, or hydatid membranes (picture 2). Percutaneous aspiration of liver cyst contents is associated with very low rates of complications, but this method of diagnosis is generally reserved for situations when other diagnostic methods are inconclusive because of the potential for anaphylaxis and secondary spread of the infection [82-85].
Active cysts have clear, watery fluid containing scolices and elevated pressure; inactive cysts have cloudy fluid without detectable scolices and do not have elevated pressure [33]. In the setting of lung cysts, protoscolices or degenerated hooklets may be demonstrable in sputum or bronchial washings. A variety of staining methods to detect parasitic material can be used. Stains for visualization of hydatid elements include Ryan trichrome blue stain and modified Baxby stain. Ziehl-Neelsen stain is also useful; under green excitation light (546 nm), the hydatid elements have a fluorescent bright red appearance [86].
If aspiration is required, it should be performed under ultrasound or CT guidance; complications can be minimized by concurrent administration of albendazole and praziquantel [27]. (See "Echinococcosis: Treatment".)
Endoscopy — Endoscopic retrograde cholangiopancreatography (ERCP) may be warranted to evaluate for biliary involvement, particularly in patients with cholestatic jaundice.
Endoscopy may demonstrate hydatid membranes within the duodenum or impacted in the papilla of Vater (picture 3). Forms of intraductal filling defect findings observed via ERCP may include laminated membranes (filamentous appearance), fragmented membranes (irregular leaf-like appearance), or amorphous debris (brown, thick appearance).
Differential diagnosis — In general, any mass occupying lesion may clinically resemble an echinococcal cyst. The differential diagnosis of cystic echinococcosis includes [87]:
●Simple benign cyst – Patients with symptomatic liver cyst may present with abdominal discomfort, pain, or nausea. Liver cysts are distinguished from Echinococcus by ultrasonography. (See "Diagnosis and management of cystic lesions of the liver".)
●Hemangioma – Hemangioma is usually an incidental finding identified in the setting of radiographic imaging or laparotomy; the most common symptoms are abdominal pain and right upper quadrant fullness. The diagnosis of hemangioma is generally established radiographically. (See "Hepatic hemangioma".)
●Hepatocellular carcinoma – Patients with hepatocellular carcinoma are usually asymptomatic in the early stages; they are distinguished from patients with cystic Echinococcus based on clinical history and imaging. (See "Clinical features and diagnosis of hepatocellular carcinoma".)
●Abscess – A liver or lung abscess may resemble an Echinococcus cyst clinically and radiographically. Liver abscess is evaluated by aspiration; lung abscess may be evaluated via bronchoscopy or aspiration. In the setting of suspicion for echinococcosis, percutaneous aspiration or biopsy should be reserved for situations when other diagnostic methods are inconclusive because of the potential for anaphylaxis and secondary spread of the infection. (See "Pyogenic liver abscess" and "Lung abscess in adults".)
●Tuberculosis – A cavitary tuberculosis lesion may resemble an Echinococcus cyst on radiographic imaging. The diagnosis of tuberculosis is established based on the presence of acid-fast bacilli on smear and culture. (See "Pulmonary tuberculosis: Clinical manifestations and complications".)
The differential diagnosis of alveolar Echinococcus includes:
●Cirrhosis – Patients with cirrhosis may have anorexia, weight loss, weakness, and fatigue; patients with alveolar Echinococcus may have malaise, weight loss, and right upper quadrant discomfort. The two are distinguished based on radiographic imaging and laboratory data. (See "Cirrhosis in adults: Etiologies, clinical manifestations, and diagnosis".)
●Malignancy (hepatocellular carcinoma or liver metastases) – Patients with liver tumors are generally distinguished from those with alveolar Echinococcus based on radiographic imaging. (See "Approach to the adult patient with an incidental solid liver lesion".)
ALVEOLAR ECHINOCOCCOSIS (E. MULTILOCULARIS)
Clinical manifestations — Infection due to E. multilocularis is usually symptomatic, although the clinical manifestations are frequently nonspecific. The most common presenting complaints include malaise, weight loss, and right upper quadrant discomfort due to hepatomegaly. Cholestatic jaundice, cholangitis, portal hypertension, and the Budd-Chiari syndrome can also occur. The clinical presentation may mimic that of hepatocellular carcinoma.
Extrahepatic primary disease is very rare (1 percent of cases). Multiorgan disease was described in 13 percent of cases in one series in which metacestodes involved the lungs, spleen, or brain in addition to the liver [46]. Immunodeficiency, such as human immunodeficiency virus (HIV) or transplantation, may accelerate the manifestations of alveolar echinococcosis (AE) [88].
If left untreated, more than 90 percent of patients will die within 10 years of the onset of clinical symptoms, and virtually 100 percent will die by 15 years [89]. Since treatment with albendazole has been introduced, the prognosis has improved considerably. Of 117 patients from France who underwent long-term follow-up, the actuarial survival rate was 88 percent [90]. Life expectancy has improved, and patients undergoing radical treatment have a better outcome now than 40 years ago. In Switzerland in 1970, the life expectancy for an average 54-year-old patient with echinococcosis was estimated to be reduced by 18 and 21 years for males and females, respectively; by 2005, life expectancy was reduced by approximately 3.5 and 2.6 years for males and females, respectively [90].
Nonspecific leukopenia or thrombocytopenia, mild eosinophilia, and nonspecific liver function abnormalities may be detected but are not diagnostic. Hypergammaglobulinemia and elevated serum IgE levels are present in more than 50 percent of cases.
Diagnosis — The diagnosis of E. multilocularis is generally made by imaging techniques in conjunction with serology.
For asymptomatic individuals in endemic areas, screening with imaging and serology has been found useful in epidemiologic studies [27]; outside of endemic areas, the role of screening for asymptomatic individuals is uncertain [28].
Imaging — On ultrasound or CT, the lesions usually have an irregular contour with no well-defined wall, central necrosis, and irregular intralesional and wall calcifications (table 3). They may be difficult to distinguish from a tumor, but the patient's overall condition is usually better than would be expected for a malignancy. The WHO Informal Work Group on echinococcosis has developed the PNM classification system, which stands for extension of the parasitic mass in the liver (P), the involvement of neighboring organs (N), and metastases (M). The system serves as a benchmark for the evaluation of diagnostic and therapeutic measures.
Obstruction of the inferior vena cava or of the portal venous system may be evident, which may be more easily appreciated on MRI. Lung, brain, and bone lesions may also be detected.
Serology — Serologic tests are more reliable for diagnosis of E. multilocularis infection than for E. granulosus infection; sensitivity and specificity rates are 95 to 100 percent [91]. A specific E. multilocularis antigen such as the affinity purified Em2 antigen from AE metacestodes is often used; the Em2-ELISA can discriminate between E. granulosus and E. multilocularis in 95 percent of cases. Serology usually remains positive indefinitely; following complete surgical resection, serology may normalize within a few years [92]. The Em2-ELISA frequently becomes negative within four years of surgery and becomes positive again in the setting of a recurrence [91,93,94]. An Em2plus-ELISA assay uses additional species-specific antigens; it has sensitivity and specificity of 97 and 99 percent, respectively, and is also useful for monitoring recurrence following surgical resection [81,95,96]. These tests may not be readily available and may be found only in specialized centers.
ELISA and immunoblot studies using Em 18, an 18-kD protoscolex antigen, are sensitive and highly species specific [65,97-101]. The antigen is also useful for differentiating between active and inactive infection and is useful for follow-up of patients on treatment [96,97,102,103].
Clinical recurrence is frequently associated with rising serologic titers. IgG1 and IgG4 antibodies are the most sensitive isotypes for monitoring success of therapy [97].
Differential diagnosis — The differential diagnosis for AE is as for cystic echinococcosis. (See 'Differential diagnosis' above.)
SUMMARY
●Clinical manifestations
•Echinococcus granulosus – E. granulosus infection is initially asymptomatic and may remain so for many years. Subsequent clinical features and complications depend upon the site and size of the cyst(s). The liver and lungs are affected in approximately 67 and 25 percent of cases, respectively. Most patients have single-organ involvement, and a single cyst is present in more than 70 percent of cases. The long-term outcome is variable and many patients remain asymptomatic. (See 'Clinical manifestations' above.)
•Echinococcus multilocularis – E. multilocularis infection is more likely to be symptomatic than E. granulosus infection. The most common clinical manifestations include right upper quadrant discomfort, malaise, and weight loss, and the picture may mimic that associated with hepatocellular carcinoma. In the absence of treatment, more than 90 percent of patients with alveolar echinococcosis die within 10 years of the onset of clinical symptoms. (See 'Clinical manifestations' above.)
●Diagnosis − The diagnosis of echinococcosis is typically established by ultrasound imaging (table 1 and image 2 and table 3) in combination with serologic testing (usually enzyme-linked immunosorbent assay). Percutaneous aspiration or biopsy should be reserved for situations when other diagnostic methods are inconclusive because of the potential for anaphylaxis and secondary spread of the infection. (See 'Diagnosis' above.)
•Ultrasonography − Hydatid disease is probable in the setting of ultrasound demonstrating infoldings of the inner cyst wall, separation of the hydatid membrane from the wall of the cyst, or hydatid sand. E. multilocularis lesions may have an irregular contour and may be difficult to differentiate from tumor. (See 'Ultrasonography' above.)
•Serology − Diagnostic judgment must take into consideration the limitations of serologic testing. The likelihood of a positive serology depends on cyst location and viability. Patients with liver cysts are more likely to be seropositive than patients with lung cysts. Serologic assays are less likely to be positive in the setting of calcified or nonviable cysts. In addition, the sensitivity and specificity of serology is greater for E. multilocularis than for E. granulosus. (See 'Serologic tests' above.)
•Cyst aspiration or biopsy − If aspiration is required, it should be performed under ultrasound or CT guidance. Complications can be minimized by concurrent administration of albendazole and praziquantel. (See 'Cyst aspiration or biopsy' above.)
ACKNOWLEDGMENT — The editorial staff at UpToDate acknowledge Dr. Karin Leder and Dr. Peter Weller, who contributed to an earlier version of this topic review.
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