Echinococcosis: a review

Background: Human alveolar echinococcosis (AE) is known to be common in certain rural communities in China whilst it is generally rare and sporadic elsewhere. The objective of this study was to provide a first estimate of the global incidence of this disease by country. The second objective was to estimate the global disease burden using age and gender stratified incidences and estimated life expectancy with the disease from previous results of survival analysis. Disability weights were suggested from previous burden studies on echinococcosis. Methodology/Principal Findings: We undertook a detailed review of published literature and data from other sources. We were unable to make a standardised systematic review as the quality of the data was highly variable from different countries and hence if we had used uniform inclusion criteria many endemic areas lacking data would not have been included. Therefore we used evidence based stochastic techniques to model uncertainty and other modelling and estimating techniques, particularly in regions where data quality was poor. We were able to make an estimate of the annual global incidence of disease and annual disease burden using standard techniques for calculation of DALYs. Our studies suggest that there are approximately 18,235 (CIs 11,900–28,200) new cases of AE per annum globally with 16,629 (91%) occurring in China and 1,606 outside China. Most of these cases are in regions where there is little treatment available and therefore will be fatal cases. Based on using disability weights for hepatic carcinoma and estimated age and gender specific incidence we were able to calculate that AE results in a median of 666,434 DALYs per annum (CIs 331,000-1.3 million). Conclusions/Significance: The global burden of AE is comparable to several diseases in the neglected tropical disease cluster and is likely to be one of the most important diseases in certain communities in rural China on the Tibetan plateau.

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The global burden of alveolar echinococcosis.

The biology of Echinococcus, the causative agent of echinococcosis (hydatid disease) is reviewed with emphasis on the developmental biology of the adult and metacestode stages of the parasite. Major advances include determining the origin, structure and functional activities of the laminated layer and its relationship with the germinal layer; and the isolation, in vitro establishment and characterization of the multipotential germinal cells. Future challenges are to identify the mechanisms that provide Echinococcus with its unique developmental plasticity and the nature of activities at the parasite-host interface, particularly in the definitive host. The revised taxonomy of Echinococcus is presented and the solid nomenclature it provides will be essential in understanding the epidemiology of echinococcosis.

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Biology and Systematics of Echinococcus.

Publisher Summary This chapter focuses on the public health importance of taeniid cestode zoonoses especially cystic echinococcosis, alveolar echinococcosis and T. solium cysticercosis. The chapter addresses the problem of neurocysticercosis and epilepsy in developing countries particularly Latin America and its public health consequences in the USA and elsewhere. E. multilocularis , which is the cause of one of the most pathogenic of all human parasitic infections, appears to be spreading in parts of western Europe, USA, and Japan. The remarkable development in the past 20 years or so of high resolution imaging technologies, such as computerized tomography (CT) scan and ultrasound have enabled precision detection of taeniid larval cystic infection in humans. Coupled with improvements in immunodiagnostic test sensitivity and antigen specificity, diagnosis of cestode zoonoses is now more accurate than ever before. Although further developments in immunodiagnosis are required, laboratory tests have provided improved capability for screening populations in both epidemiological and community studies. Parallel and recent development of genus specific coproantigen tests for human taeniasis and canine echinococcosis have also provided major new tools for epidemiological and surveillance programs.

Detection, screening and community epidemiology of taeniid cestode zoonoses: cystic echinococcosis, alveolar echinococcosis and neurocysticercosis.

Human alveolar echinococcosis (AE), caused by the metacestode of the fox tapeworm Echinococcus multilocularis, is the most pathogenic zoonosis in temperate and arctic regions of the northern hemisphere. Prospective collection of human cases in some areas and mass screenings using ultrasound imaging and confirmation with serological techniques have markedly improved our knowledge of the epidemiology of the disease in humans during the past two decades. Transmission occurs when eggs of the tapeworm, excreted by the final hosts (usually foxes but also dogs, wolves and cats), are ingested accidentally by humans or during normal feeding by a variety of rodents and small lagomorphs. However, the species of host animals differ according to regional changes in mammalian fauna. This review mostly focuses on epidemiology of alveolar echinococcosis in those parts of the world where new and more accurate epidemiological data are now available, i.e. China and Europe, as well as on new epidemiological trends that can be suspected from recent case reports and/or from recent changes in animal epidemiology of E. multilocularis infection. The People's Republic of China (PRC) is a newly recognized focus on AE in Asia. Human AE cases were firstly recognized in Xinjiang Uygur Autonomous Region and Qinghai Provinces at the end of 1950s and infected animals were first reported from Ningxia in central China and northeast of Inner Mongolia in the 1980s. E. multilocularis (and human cases of AE) appears to occur in three areas: (1) Northeastern China (northeast focus): including Inner Mongolia Autonomous region and Heliongjiang Province (2) Central China (central focus): including Gansu Province, Ningxia Hui Autonomous Region, Sichuan Province, Qinghai Province and Tibet Autonomous Region and (3) Northwestern China: including Xinjiang Uygur Autonomous Region, bordered with Mongolia, Russia, Kazakhstan and Kyrgyzstan. The highest prevalence of the disease, up to 15 per cent of the population in some villages, is reached in China. In Europe, data from the European Echinococcosis Registry (EurEchinoReg: 1982-2000) show 53 autochthonous cases of AE in Austria, 3 in Belgium, 235 in France, 126 in Germany, 1 in Greece, and 112 in Switzerland, and 15 'imported' cases, especially from central Asia; 14 cases were collected in Poland, a country not previously considered endemic for AE. Improved diagnostic technology, as well as a real increase in the infection rate and an extension to new areas, can explain that more than 500 cases have been reported for these 2 decades while less than 900 cases were published for the previous 7 decades. New epidemiological trends are related to an unprecedented increase in the fox population in Europe, to the unexpected development of urban foxes in Japan and in Europe, and to changes in the environmental situation in many countries worldwide due to climatic or anthropic factors which might influence the host-predator relationship in the animal reservoir and/or the behavioural characteristics of the populations in the endemic areas.

Epidemiology of alveolar echinococcosis with particular reference to China and Europe.

The clinical features of 33 cases of alveolar hydatid disease (AHD) in Alaskan Eskimos and a review of the surgical experience with this disease are presented. Among untreated patients, progression of the disease to a fatal outcome was observed in 70%. The primary hepatic lesion resembles cancer, and errors in diagnosis by both the surgeon and pathologist are common. Although surgical resection of the entire primary hepatic lesion offers the only proven curative treatment, only 26% of those explored were resectable. All seven patients resected for cure are alive 6-27 years post-operatively (average survival, 14.7 years). A 5-year experience with continuous mebendazole therapy in the management of five nonresectable cases of AHD indicates that a favorable effect of this drug is being observed. It now appears that Echinococcus infections are no longer the sole province of the surgeon. Although the role of medical therapy is not yet clearly defined, it must be considered in the management of all cases of AHD. The first reported locally-acquired case of AHD in the conterminous United States, and the widespread occurrence and expanding range of E. multilocularis in the north-central United States and south-central Canada, point to the increasing public health importance of alveolar hydatid disease.

R L Rausch

Papers

Alveolar hydatid disease. A review of clinical features of 33 indigenous cases of Echinococcus multilocularis infection in Alaskan Eskimos.