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Review
, 17 (1), 107-35

Biological, Epidemiological, and Clinical Aspects of Echinococcosis, a Zoonosis of Increasing Concern

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Review

Biological, Epidemiological, and Clinical Aspects of Echinococcosis, a Zoonosis of Increasing Concern

Johannes Eckert et al. Clin Microbiol Rev.

Abstract

Echinococcosis in humans is a zoonotic infection caused by larval stages (metacestodes) of cestode species of the genus Echinococcus. Cystic echinococcosis (CE) is caused by Echinococcus granulosus, alveolar echinococcosis (AE) is caused by E. multilocularis, and polycystic forms are caused by either E. vogeli or E. oligarthrus. In untreated cases, AE has a high mortality rate. Although control is essentially feasible, CE remains a considerable health problem in many regions of the northern and southern hemispheres. AE is restricted to the northern hemisphere regions of North America and Eurasia. Recent studies have shown that E. multilocularis, the causative agent of AE, is more widely distributed than previously thought. There are also some hints of an increasing significance of polycystic forms of the disease, which are restricted to Central and South America. Various aspects of human echinococcosis are discussed in this review, including data on the infectivity of genetic variants of E. granulosus to humans, the increasing invasion of cities in Europe and Japan by red foxes, the main definitive hosts of E. multilocularis, and the first demonstration of urban cycles of the parasite. Examples of emergence or reemergence of CE are presented, and the question of potential spreading of E. multilocularis is critically assessed. Furthermore, information is presented on new and improved tools for diagnosing the infection in final hosts (dogs, foxes, and cats) by coproantigen or DNA detection and the application of molecular techniques to epidemiological studies. In the clinical field, the available methods for diagnosing human CE and AE are described and the treatment options are summarized. The development of new chemotherapeutic options for all forms of human echinococcosis remains an urgent requirement. A new option for the control of E. granulosus in the intermediate host population (mainly sheep and cattle) is vaccination. Attempts are made to reduce the prevalence of E. multilocualaris in fox populations by regular baiting with an anthelmintic (praziquantel). Recent data have shown that this control option may be used in restricted areas, for example in cities, with the aim of reducing the infection risk for humans.

Figures

FIG. 1.
FIG. 1.
Life cycle of E. granulosus (common sheep strain). (A) Adult parasite. (B) Domestic dog as principal definitive host; wild canids (dingo, hyena etc.) can be involved in the cycle. (C) Proglottid with eggs. (D) Egg with oncosphere. (E) Infection of humans. (F) Sheep as principal intermediate hosts; other ungulates are of lower significance. (G) sheep liver with cysts.
FIG. 2.
FIG. 2.
Hepatic CE in a patient (endocyst removed; lesion size approximately 3 by 3.5 cm).
FIG. 3.
FIG. 3.
Ultrasonograms of hepatic cysts of E. granulosus (Top) Type CL of WHO-IGWE classification (see text): lesion (arrows) with uniform anechoic content, not clearly delimited by an hyperechoic rim (cvst wall not visible). (Bottom) Type CE2: multivesicular cysts. Reprinted with permission from P. Kern and Dr. W. Kratzer, University Hospital and Medical Center, University of Ulm, Ulm, Germany.
FIG. 4.
FIG. 4.
Horse liver with multiple cysts of E. granulosus (cyst diameters approximately 1 to 10 cm). The horse exhibited clinical signs of the disease.
FIG. 5.
FIG. 5.
Approximate global distribution of E. granulosus (as of 2002). The exact identification of areas of normal and high endemicity is difficult because of incomplete or lacking data. Modified from WHO/OIE 2001 (223) with permission.
FIG. 6.
FIG. 6.
Life cycle of E. multilocularis. (A) Adult parasite. (B) Foxes (left, red fox; right, Arctic fox) as principal definitive hosts; dogs, other canids, and cats can be involved in the cycle. (C) Proglottid with eggs. (D) Egg with oncosphere. (E) Infection of humans. (F) Rodent infected with metacestodes. (G) Rodent liver with metacestodes. (H) single metacestode cyst with protoscoleces.
FIG. 7.
FIG. 7.
Hepatic alveolar echinococcosis in a 62-year-old Swiss patient (maximum diameter of single cysts approximately 1.5 cm).
FIG. 8.
FIG. 8.
Hepatic alveolar echinococcosis in a dog.
FIG. 9.
FIG. 9.
Approximate global distribution of E. multilocularis (as of 2002). Exact identification of areas of normal and high endemicity is difficult becaue of incomplete or lacking data. Modified from WHO/OIE 2001 (223) with permission.
FIG. 10.
FIG. 10.
Life cycle of E. vogeli. (A): Adult parasite. (B) Bush dog (Speothos venaticus) as principal definitive host (B1); domestic dogs are rarely infected (B2). (C) Proglottid with eggs. (D) Egg with oncosphere. (E) Infection of humans. (F) Intermediate hosts: paca (Cuniculus paca) (F1) and agouti (Dasyprocta spp.) (F2). Data from reference 180.
FIG. 11.
FIG. 11.
Life cycle of E. oligarthrus. (A) adult parasite. (B) Wild felids as definitive hosts: cougar (Felis concolor) (B1), jaguar (Panthera onca) (B2), and ocelot (Felis pardalis) (B3) as examples. (C) Proglottid with eggs. (D) Egg with oncosphere. (E) Infection of humans. (F) Intermediate hosts: agouti (Dasyprocta spp.) (F1) spiny rat (Proechimys spp.) (F2), and paca (Cuniculus paca) (F3). Data from reference 180.

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