Review
Prevention and control of cystic echinococcosis

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Summary

Human cystic echinococcosis (hydatid disease) continues to be a substantial cause of morbidity and mortality in many parts of the world. Elimination is difficult to obtain and it is estimated that, using current control options, achieving such a goal will take around 20 years of sustained efforts. Since the introduction of current (and past) hydatid control campaigns, there have been clear technological improvements made in the diagnosis and treatment of human and animal cystic echinococcosis, the diagnosis of canine echinococcosis, and the genetic characterisation of strains and vaccination against Echinococcus granulosus in animals. Incorporation of these new measures could increase the efficiency of hydatid control programmes, potentially reducing the time required to achieve effective prevention of disease transmission to as little as 5–10 years.

Introduction

Cystic and alveolar echinococcosis (hydatid disease) are a cause of substantial morbidity and mortality in most of the world, including parts of Europe, North America, and South America (figure 1). Recent technological advances could facilitate the implementation of improved control programmes and reduce the time period required for elimination. In this Review, we summarise and update information presented and discussed at a workshop on the control of cystic hydatid disease held in May, 2005, in Lima, Peru, under the sponsorship of the Office of Rare Diseases, National Institutes of Health (Bethesda, MD, USA) and the Universidad Peruana Cayetano Heredia (Lima, Peru). Reflecting the presented material, this paper mainly focuses on Echinococcus granulosus infections, with some discussion of specific areas relating to Echinococcus multilocularis and alveolar hydatid disease.

Section snippets

The parasites

Hydatidosis is a chronic cyst-forming parasitic helminthic disease of human beings as well as domestic and wild ungulates. It is caused by infection with the larval (metacestode) stages of dog tapeworms belonging to the genus Echinococcus (family Taeniidae) and is also referred to as echinococcosis. Three broad morphological forms of echinococcosis are recognised clinically: cystic echinococcosis caused by E granulosus, alveolar echinococcosis caused by E multilocularis, and polycystic

Echinococcus spp diagnosis, detection, and pathology

Diagnosis of human echinococcosis remains highly dependent on imaging techniques (eg, computed tomography scan, magnetic resonance imaging, ultrasound, and radiography) to detect the space-occupying cysts or lesions caused by the developing, dying, or dead metacestode(s) of Echinococcus spp.1, 3, 9, 12, 13, 14, 15 (Figure 2, Figure 3). The WHO expert group on echinococcosis has produced an international classification of ultrasound images of cystic echinococcosis which, in principle, should be

Epidemiology and control

Epidemiologically, human cystic echinococcosis occurs predominantly in poor pastoral communities that raise sheep and other livestock, and keep dogs for guarding and/or herding animals. E granulosus is mainly transmitted in a cycle between dog definitive hosts that harbour the small intestinal tapeworm, and livestock (especially sheep) after the latter ingest the microscopic eggs while grazing pastures that are contaminated with dog faeces.1 Dogs usually acquire infection from hydatid-carrying

Relevance of species and genotype of E granulosus

E granulosus comprises a number of genetic variants and, to date, analyses of mitochondrial DNA sequences have identified ten distinct genetic types (genotypes G1–10). This categorisation follows closely the pattern of strain variation emerging based on biological characteristics. The extensive variation in nominal E granulosus may influence life-cycle patterns, host specificity, development rate, antigenicity, transmission dynamics, sensitivity to chemotherapeutic agents, and pathology. It

Dog coproantigen detection

The diagnosis of E granulosus in dogs using coproantigen-detection ELISA method has a number of advantages over the use of arecoline purgation as a diagnostic test. Coproantigen-detection ELISA has easier sample collection, is faster to do, and requires less personnel, all of which make it suitable for surveillance of large dog populations.43 Unlike arecoline purgation (which requires taking dogs to purge sites and concentration of dogs in specific places), faecal samples for coproantigen

Vaccines against E granulosus

Control programmes against cystic echinococcosis have traditionally relied on anthelmintic dosing of dogs, improved slaughter hygiene and surveillance, and instigated health education relating to human–dog behaviour.1, 9, 81, 84, 85 Echinococcus vaccines would ideally prevent oncosphere development to hydatid cysts in sheep, and thus stop the development of adult gravid tapeworms in dogs.40, 86, 87, 88, 89 (figure 5).

A defined recombinant vaccine for ovine cystic echinococcosis (called EG95)

Reasons for failure of E granulosus control programmes

Until now, only the five island-based hydatid control programmes (Iceland, New Zealand, Tasmania, Falkland Islands, and Cyprus) have been successful, mostly based on health education, control, or elimination of home slaughter of sheep. A decline in canine infection was followed by a drop in the prevalence of infection in sheep and young cattle and a decreasing annual incidence of human cases.112 By contrast, only two of the continental programmes in Latin America (Region XII in Chile, and Rio

Control of E multilocularis

By contrast with the predominant domestic animal transmission cycles that sustain E granulosus worldwide, the closely related species E multilocularis is transmitted only in the northern hemisphere and mainly within wildlife cycles. A number of fox species are highly susceptible to infection with the adult tapeworm, and a wide range of rodents (especially microtine voles) and small mammals can act as intermediate hosts. Human infection with the larval stage, alveolar echinococcosis, is

Shortcomings of control interventions and additional measures to improve efficacy

Dog treatment campaigns face the problem of coverage, incomplete sensitivity to identify positive dogs, and incomplete treatment effectiveness. Associated costs and the need for equipment (eg, ELISA reader) are major limitations with the coproantigen ELISA test in endemic areas. The application of the test in areas of low endemicity can be hampered by a predictive positive value that would be expected to be low and where potential cross-reactions with other Taenia spp may occur.127

Although

Conclusion

Hydatid disease remains endemic in many regions around the world. Advances in knowledge and development/design of new control tools for hydatid disease including new diagnostics and antiparasite vaccines for the definitive and intermediate hosts provide an excellent prospect for improved control programmes. Incorporation of these new measures has the potential to increase the efficiency of current control programmes and could reduce the time required to achieve effective prevention of disease

Search strategy and selection criteria

Most information for this Review comes from ongoing work from the authors or was identified through searches of their extensive files. Additional references were identified by searches of Medline between 1969 and 2006, and references from relevant articles. The search terms “hydatidosis”, “hydatid disease”, or “Echinococcus” were used. Papers published in English or Spanish were reviewed. The final reference list was generated based on relevance to the topics covered in the Review.

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