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. Ultrasonographic appearance of echinococcal cysts is seen in the image below.
WHO Informal Working Group on Echinococcosis standardized ultrasound classification of echinococcal cysts. Image courtesy of World Health Organization (WHO). 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.
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. 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.
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.
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. 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.
Pathophysiology
In primary echinococcosis, 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 echinococcosis, larval cysts may develop in every organ. Most patients (as many as 80%) have single-organ involvement and harbor a solitary cyst. Approximately two thirds of patients experience liver echinococcosis. The second most common organ involved is the lung.
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 are often detected. The growth rate of cysts is highly variable and may depend on strain differences. Estimates of the average increase of cyst diameter vary (approximately 1-1.5 cm/y).
The clinical features of cystic echinococcosis are highly variable. The spectrum of symptoms depends on the following:
- Involved organs
- Size of cysts and their sites within the affected organ or organs
- Interaction between the expanding cysts and adjacent organ structures, particularly bile ducts and the vascular system of the liver
- Complications caused by rupture of cysts
- Bacterial infection of cysts and spread of protoscolices and larval material into bile ducts or blood vessels
- Immunologic reactions such as asthma, anaphylaxis, or membranous nephropathy secondary to release of antigenic material
Epidemiology
Frequency
United States
Unfortunately, realistic national or international figures do not exist for total numbers of cases of cystic echinococcosis. The problem is that, until recently, the only basis for diagnosis was surgery, and few countries systematically reported cases. When they did report cases, uneven reporting occurred in different regions of countries. The groups most at risk of cystic echinococcosis are usually underserved by medical services.
However, the increasing use of mass screenings with ultrasonography in endemic countries is generating important epidemiological data. As different cyst stages have been classified according to their sonographic appearance, attempts are being made to match the cyst morphology with the natural history of the cyst. This is evident with the World Health Organization (WHO) standardized classification (see Imaging). At a community level, the relative proportions of cyst types can provide epidemiological information on disease transmission and help design effective control programs.[1]
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.
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
Cystic echinococcosis 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 being conducted to evaluate the burden of disease, including nonmonetary costs.
Mortality/Morbidity
Cystic echinococcosis is rarely fatal. Occasionally, deaths occur because of anaphylactic shock or cardiac tamponade in heart echinococcosis.[2]
Rare locations of the cyst (muscle, bone, brain, orbit) can cause dramatic and disabling symptoms (blindness, paralysis).[3, 4, 5, 6, 7, 8, 9, 10]
Race
No racial predilection exists.
Sex
In some endemic countries, females are affected more than males because their lifestyle habits and practices bring them into contact with the parasite.
Age
Individuals of all ages are affected. In some endemic countries, children have higher infection rates because they are most likely to play with dogs.
Larrieu E, Del Carpio M, Mercapide CH, Salvitti JC, Sustercic J, Moguilensky J, et al. Programme for ultrasound diagnoses and treatment with albendazole of cystic echinococcosis in asymptomatic carriers: 10 years of follow-up of cases. Acta Trop. Jan 2011;117(1):1-5. [Medline].
Bouraoui H, Trimeche B, Mahdhaoui A, Majdoub A, Zaaraoui J, Hajri Ernez S, et al. Echinococcosis of the heart: clinical and echocardiographic features in 12 patients. Acta Cardiol. Feb 2005;60(1):39-41. [Medline].
Biyik I, Acar S, Ergene O. Left atrial mobile hydatid cyst mimicking left atrial myxoma and mitral stenosis and causing heart failure and arrhythmia. Int J Cardiovasc Imaging. Apr 2007;23(2):193-5. [Medline].
Tsaroucha AK, Polychronidis AC, Laftsidis PA, Pitiakoudis MS, Fotakis SN, Simopoulos CE. Primary adrenal hydatid cyst: a case report. Acta Chir Iugosl. 2007;54(2):115-7. [Medline].
Tutar N, Cakir B, Geyik E, Tarhan NC, Niron EA. Hydatid cysts in breast: mammography and ultrasound findings. Br J Radiol. Oct 2006;79(946):e114-6. [Medline].
Türkmen C, Unal SN, Berberoglu K, Genchellac H, Unal Z, Cantez S. Acute pulmonary embolism due to hydatid cyst. Clin Nucl Med. Nov 2004;29(11):760-1. [Medline].
Yuksel BC, Ozel H, Akin T, Avsar FM, Hengirmen S. Primary hydatid cyst of the breast with elevated CA 19-9 level. Am J Trop Med Hyg. Aug 2005;73(2):368-70. [Medline].
Pamir MN, Ozduman K, Elmaci I. Spinal hydatid disease. Spinal Cord. Apr 2002;40(4):153-60. [Medline].
Bulman W, Coyle CM, Brentjens TE, Horn EM, Dickstein ML, Wilt JS. Severe pulmonary hypertension due to chronic echinococcal pulmonary emboli treated with targeted pulmonary vascular therapy and hepatic resection. Chest. Oct 2007;132(4):1356-8. [Medline].
Bron JL, van Kemenade FJ, Verhoof OJ, Wuisman PI. Long term follow-up of a patient with disseminated spinal hydatidosis. Acta Orthop Belg. Oct 2007;73(5):678-82. [Medline].
Nagpal V, Kohli K, Chowdhary A, Kumar A, Andley M, Ravi B. Breast lump as a presentation of a hydatid disease. Trop Doct. Jan 2006;36(1):57-8. [Medline].
Santivanez S, Garcia HH. Pulmonary cystic echinococcosis. Curr Opin Pulm Med. May 2010;16(3):257-61. [Medline].
[Guideline] Brunetti E, Kern P, Vuitton DA,. Expert consensus for the diagnosis and treatment of cystic and alveolar echinococcosis in humans. Acta Trop. Apr 2010;114(1):1-16. [Medline].
Macpherson CN, Bartholomot B, Frider B. Application of ultrasound in diagnosis, treatment, epidemiology, public health and control of Echinococcus granulosus and E. multilocularis. Parasitology. 2003;127 Suppl:S21-35. [Medline].
Gharbi HA, Hassine W, Brauner MW, Dupuch K. Ultrasound examination of the hydatic liver. Radiology. May 1981;139(2):459-63. [Medline].
WHO Informal Working Group. International classification of ultrasound images in cystic echinococcosis for application in clinical and field epidemiological settings. Acta Trop. Feb 2003;85(2):253-61. [Medline].
Junghanss T, da Silva AM, Horton J, Chiodini PL, Brunetti E. Clinical management of cystic echinococcosis: state of the art, problems, and perspectives. Am J Trop Med Hyg. Sep 2008;79(3):301-11. [Medline].
Brunetti E, Junghanss T. Update on cystic hydatid disease. Curr Opin Infect Dis. Oct 2009;22(5):497-502. [Medline].
Hosch W, Junghanss T, Stojkovic M, Brunetti E, Heye T, Kauffmann GW. Metabolic viability assessment of cystic echinococcosis using high-field 1H MRS of cyst contents. NMR Biomed. Aug 2008;21(7):734-54. [Medline].
Hosch W, Stojkovic M, Jänisch T, Kauffmann GW, Junghanss T. The role of calcification for staging cystic echinococcosis (CE). Eur Radiol. Oct 2007;17(10):2538-45. [Medline].
Dursun M, Terzibasioglu E, Yilmaz R, Cekrezi B, Olgar S, Nisli K, et al. Cardiac hydatid disease: CT and MRI findings. AJR Am J Roentgenol. Jan 2008;190(1):226-32. [Medline].
Hosch W, Stojkovic M, Jänisch T, Heye T, Werner J, Friess H, et al. MR imaging for diagnosing cysto-biliary fistulas in cystic echinococcosis. Eur J Radiol. May 2008;66(2):262-7. [Medline].
Neumayr A, Troia G, de Bernardis C, Tamarozzi F, Goblirsch S, Piccoli L, et al. Justified concern or exaggerated fear: the risk of anaphylaxis in percutaneous treatment of cystic echinococcosis-a systematic literature review. PLoS Negl Trop Dis. Jun 2011;5(6):e1154. [Medline]. [Full Text].
Stojkovic M, Zwahlen M, Teggi A, Vutova K, Cretu CM, Virdone R, et al. Treatment response of cystic echinococcosis to benzimidazoles: a systematic review. PLoS Negl Trop Dis. Sep 29 2009;3(9):e524. [Medline]. [Full Text].
Liu Y, Wang X, Wu J. Continuous long-term albendazole therapy in intraabdominal cystic echinococcosis. Chin Med J (Engl). Sep 2000;113(9):827-32. [Medline].
Bygott JM, Chiodini PL. Praziquantel: neglected drug? Ineffective treatment? Or therapeutic choice in cystic hydatid disease?. Acta Trop. Aug 2009;111(2):95-101. [Medline].
El Malki HO, El Mejdoubi Y, Souadka A, Mohsine R, Ifrine L, Abouqal R, et al. Predictive factors of deep abdominal complications after operation for hydatid cyst of the liver: 15 years of experience with 672 patients. J Am Coll Surg. Apr 2008;206(4):629-37. [Medline].
Bagheri R, Haghi SZ, Amini M, Fattahi AS, Noorshafiee S. Pulmonary hydatid cyst: analysis of 1024 cases. Gen Thorac Cardiovasc Surg. Feb 2011;59(2):105-9. [Medline].
Li Y, Zheng H, Cao X, Liu Z, Chen L. Demographic and clinical characteristics of patients with anaphylactic shock after surgery for cystic echinococcosis. Am J Trop Med Hyg. Sep 2011;85(3):452-5. [Medline]. [Full Text].
Filice C, Pirola F, Brunetti E, Dughetti S, Strosselli M, Foglieni CS. A new therapeutic approach for hydatid liver cysts. Aspiration and alcohol injection under sonographic guidance. Gastroenterology. May 1990;98(5 Pt 1):1366-8. [Medline].
Paksoy Y, Odev K, Sahin M, Arslan A, Koc O. Percutaneous treatment of liver hydatid cysts: comparison of direct injection of albendazole and hypertonic saline solution. AJR Am J Roentgenol. Sep 2005;185(3):727-34. [Medline].
Paksoy Y, Odev K, Sahin M, Dik B, Ergül R, Arslan A. Percutaneous sonographically guided treatment of hydatid cysts in sheep: direct injection of mebendazole and albendazole. J Ultrasound Med. Aug 2003;22(8):797-803. [Medline].
Smego RA Jr, Bhatti S, Khaliq AA, Beg MA. Percutaneous aspiration-injection-reaspiration drainage plus albendazole or mebendazole for hepatic cystic echinococcosis: a meta-analysis. Clin Infect Dis. Oct 15 2003;37(8):1073-83. [Medline].
Kabaalioglu A, Ceken K, Alimoglu E, Apaydin A. Percutaneous imaging-guided treatment of hydatid liver cysts: do long-term results make it a first choice?. Eur J Radiol. Jul 2006;59(1):65-73. [Medline].
Khuroo MS, Wani NA, Javid G, Khan BA, Yattoo GN, Shah AH, et al. Percutaneous drainage compared with surgery for hepatic hydatid cysts. N Engl J Med. Sep 25 1997;337(13):881-7. [Medline].
Men S, Yucesoy C, Edguer TR, Hekimoglu B. Percutaneous treatment of giant abdominal hydatid cysts: long-term results. Surg Endosc. Oct 2006;20(10):1600-6. [Medline].
Schipper HG, Laméris JS, van Delden OM, Rauws EA, Kager PA. Percutaneous evacuation (PEVAC) of multivesicular echinococcal cysts with or without cystobiliary fistulas which contain non-drainable material: first results of a modified PAIR method. Gut. May 2002;50(5):718-23. [Medline].
Ustunsoz B, Ugurel MS, Uzar AI, Duru NK. Percutaneous treatment of hepatic hydatid cyst in pregnancy: long-term results. Arch Gynecol Obstet. Oct 31 2007;[Medline].
Golemanov B, Grigorov N, Mitova R, Genov J, Vuchev D, Tamarozzi F. Efficacy and safety of PAIR for cystic echinococcosis: experience on a large series of patients from Bulgaria. Am J Trop Med Hyg. Jan 2011;84(1):48-51. [Medline].
Hosseini SV, Ghanbarzadeh K, Barzin J, Sadjjadi SM, Tanideh N, Mehrabani D. In vitro protoscolicidal effects of hypertonic glucose on protoscolices of hydatid cyst. Korean J Parasitol. Sep 2006;44(3):239-42. [Medline].
Brunetti E, Filice C, Meroni V. Comment on percutaneous treatment of liver hydatid cysts. AJR Am J Roentgenol. Apr 2006;186(4):1198-9; author reply 1199-200. [Medline].
Brunetti E, Gulizia R, Garlaschelli AL, Filice C. Cystic echinococcosis of the liver associated with repeated international travels to endemic areas. J Travel Med. Jul-Aug 2005;12(4):225-8. [Medline].
Budke CM. Global socioeconomic impact of cystic echinococcosis. Emerg Infect Dis. Feb 2006;12(2):296-303. [Medline].
Craig PS, McManus DP, Lightowlers MW, Chabalgoity JA, Garcia HH, Gavidia CM. Prevention and control of cystic echinococcosis. Lancet Infect Dis. Jun 2007;7(6):385-94. [Medline].
Cunha BA. Antibiotic Essentials. Royal Oak, Mich: Physicians Press; 2005.
Eckert J, Deplazes P. Biological, epidemiological, and clinical aspects of echinococcosis, a zoonosis of increasing concern. Clin Microbiol Rev. Jan 2004;17(1):107-35. [Medline].
Franchi C, Di Vico B, Teggi A. Long-term evaluation of patients with hydatidosis treated with benzimidazole carbamates. Clin Infect Dis. Aug 1999;29(2):304-9. [Medline].
Kilic M, Yoldas O, Koc M, Keskek M, Karakose N, Ertan T, et al. Can biliary-cyst communication be predicted before surgery for hepatic hydatid disease: does size matter?. Am J Surg. Nov 2008;196(5):732-5. [Medline].
Macpherson CN, Milner R. Performance characteristics and quality control of community based ultrasound surveys for cystic and alveolar echinococcosis. Acta Trop. Feb 2003;85(2):203-9. [Medline].
Magistrelli P, Masetti R, Coppola R, Messia A, Nuzzo G, Picciocchi A. Surgical treatment of hydatid disease of the liver. A 20-year experience. Arch Surg. Apr 1991;126(4):518-22; discussion 523. [Medline].
McManus DP, Zhang W, Li J, Bartley PB. Echinococcosis. Lancet. Oct 18 2003;362(9392):1295-304. [Medline].
Nasseri-Moghaddam S, Abrishami A, Taefi A, Malekzadeh R. Percutaneous needle aspiration, injection, and re-aspiration with or without benzimidazole coverage for uncomplicated hepatic hydatid cysts. Cochrane Database Syst Rev. 2011;(1):CD003623. [Medline].
Rogan MT, Hai WY, Richardson R, Zeyhle E, Craig PS. Hydatid cysts: does every picture tell a story?. Trends Parasitol. Sep 2006;22(9):431-8. [Medline].
Sayek I, Tirnaksiz MB, Dogan R. Cystic hydatid disease: current trends in diagnosis and management. Surg Today. 2004;34(12):987-96. [Medline].
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