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

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

Canine echinococcosis in Kyrgyzstan: Using prevalence data adjusted for measurement error to develop transmission dynamics models

“…Echinococcus granulosus causes human cystic echinococcosis (CE). This cestode utilises dogs as definitive hosts, has a global distribution and is a problem in many areas (for example central Asia, China, South America, Northern Africa, Australia) where grazing livestock are the major intermediate hosts (Eckert and Deplazes, 2004;Jenkins et al, 2005). Different strains of E. granulosus exist, which, according to their preferred intermediate hosts, are called the 'sheep strain' (G1), the 'horse strain' (G4) (or Echinococcus equinus) or the 'pig/camel strain' (G6/7) (Thompson and McManus, 2002;Obwaller et al, 2004).…”

Primary mediastinal hydatid disease leading to popliteal artery hydatid cyst embolization

“…The infection known as hydatidosis is a zoonotic infection caused by Echinococcus granulosus belonging to the class Cestoda. The organism lives in the small intestine of definitive hosts such as canines 6. Sheep and cattle are intermediate hosts and the echinococcal eggs enter the human body through food and water contaminated by the feces of infected canines.…”

Compound processes as models for clumped parasite data

“…The Kazakhstan sample contains 2505 individual reports of the variables age and hydatid cyst burden in sheep, caused by the parasite Echinococcus granulosus (E.g.) [32]. The Jordan sample counts 832 individual reports of the same variables.…”

“…The Jordan sample counts 832 individual reports of the same variables. Cysts do not proliferate inside their hosts, but protoscoleces are produced inside the cysts which play a role in the infection of the definitive host [32]. It can be assumed that cysts survive their hosts, that there is no parasite-induced mortality and no acquired immunity in sheep [1,32].…”

“…is also potentially dangerous for humans. For this disease, it can be assumed that the cysts survive their hosts but do not replicate, and that there is no parasite-induced mortality and no acquired immunity in sheep [1,32].…”