‘Echinococcosis’ applies to 2 rather different diseases, due respectively to E. granulosus, ‘cystic echinococcosis’ (CE), and to E. multilocularis, alveolar echinococcosis (AE). Both species differ by their usual animal reservoir, i.e. mostly domestic animals, for E. granulosus, and mostly wild animals, for E. multilocularis. Other species of Echinococcus may also cause disease in humans, E. oligarthrus and E. vogeli have a clinical presentation similar to that of CE and AE, respectively. No specific disease has been attributed until now to the recently identified species, E. shiquicus. Based on their genetic characteristics, E. granulosus has been split into several species: E. granulosus sensu stricto (ex-sheep strain), E. felidis, E. equinus (ex-horse strain, never recognized to infect humans), E. ortleppi (ex-cattle strain), and E. canadensis (ex-camel, pig and cervid strains). The larval stage of Echinococcus spp., also called ‘metacestode’ is characterized by the germinal layer surrounded by the laminated layer. The germinal layer forms ‘buds’, then ‘vesicles’ (cysts), which are filled with a water-like liquid (‘hydatid/cyst/vesicle fluid’). These cysts may be single (typically for CE) or multiple and aggregated (typically for AE). Fertility is characterized by the budding of ‘protoscoleces’ from the germinal layer, and their release into the cyst fluid. The most striking differences between E. granulosus and E. multilocularis lie in the histological aspect of the metacestodes, respectively big cysts with little inflammatory reaction and numerous protoscoleces in CE, and multiple aggregated small cysts with an impressive granulomatous periparasitic infiltration, associated with dense fibrosis, and few or no protoscoleces in AE, hence the different clinical presentations and complications. Pseudo-cysts, due to massive necrosis of the central part of lesion, may occur in advanced AE. CE is usually maintained by the synanthropic domestic cycle (dog/domestic ungulate) and represents a persistent zoonosis in rural livestock-raising areas where humans cohabit with dogs fed on raw livestock offal where the cysts are present. A cycle in wild animals allows E. multilocularis to subsist in nature. It includes voles of a number of different species depending on the area and the lagomorph Ochotona curzionae (on the Tibetan plateau of China), as intermediate hosts, and foxes, wolves and dogs, and less commonly other carnivores as definitive hosts. Larval AE infection with symptoms close to those observed in humans has been recognized in a number of domestic animals and in zoo animals or in exotic pets. Environmental factors play a critical role in E. multilocularis infection in wild animals, resulting in a heterogeneous geographical distribution of the parasite; in many countries, fox urbanization has considerably increased the human population at risk. The burden of both diseases in terms of DALY lost or economic cost has long been underestimated both in humans and animals. Host-parasite interactions in larval echinococcosis depend on a subtle balance between the various immunological mechanisms involved in protection of the host versus tolerance to the parasite. Very rare in AE, IgE-dependent allergic reactions and eosinophilia occur in CE when there are fissures or ruptures in the cyst. AE lesion progression is faster in patients with immune suppression; immunosuppressive treatments in patients with cancer or inflammatory diseases, more frequently administered since the beginning of the XXIst century, have modified the epidemiology and the presentation of AE in Europe during the last 2 decades. XXIst The diagnosis of both diseases in humans relies on imaging. Both CE and AE may remain asymptomatic for a long period of time; and spontaneous death of the metacestode does occur in many infected patients. Ultrasound (US) examination is the basis for diagnosis in patients with liver-related signs and symptoms and for mass screening. Fortuitous diagnosis of CE or AE on abdominal US images taken for another indication is not rare. Complementary imaging exams at diagnosis and for follow-up include CT-scan, Magnetic Resonance Imaging, and for AE only, Positron Emission Tomography 1 and 3 hours after IV injection of 18F-FluoroDesoxyGlucose (FDG-PET). Diagnosis is confirmed by specific serology; however, serological tests are far less sensitive in CE than in AE. The WHO-Informal Working Group on Echinococcosis has proposed a US-based classification of CE cysts (CE-1 to CE-5), and a staging system for AE (PNM classification) which should be used by clinicians to better assess the evolution potential and severity of the disease as well as to facilitate comparison between case series. Until 1980, the treatment of both CE and AE relied only on surgery. Depending on the class, stage, and size of the lesions, a variety of options are now available. For CE it includes short-term (3 months in average) albendazole treatment for small cysts or, at the opposite of the spectrum, long-term albendazole (> 6 months to several years) treatment for disseminated non-operable CE, the PAIR (puncture, aspiration, injection, reaspiration) percutaneous technique for middle-sized liver cysts without daughter vesicles. The current trend for surgery is to remove the whole cyst (‘total cystectomy’) whenever possible to avoid recurrence; ‘partial cystectomy’ with sterilisation of the cyst content by protoscolecide agents is easier to perform in all settings, but more prone to be followed by recurrence and dissemination. In AE, albendazole treatment is the basis for care management: given for a minimum of 2 years after radical surgical resection of the liver lesions, it must be administered for life in all other cases. The current trend for surgery is to avoid palliative surgery and to prefer percutaneous or perendoscopic drainage and stenting of the obstructed bile ducts and/or percutaneous drainage of the central necrotic cavity in advanced cases. In CE as well as in AE, appropriate monitoring of albendazole and of its possible adverse effects is mandatory, and long-term follow-up of each patient is crucial. For both diseases too, however, there is an urgent need to test new chemical or biological compounds for the treatment of patients who cannot be treated by albendazole, and to evaluate therapeutic strategies, including the various types of surgical operations, by prospective studies.
|Title of host publication||Zoonoses-Infections Affecting Humans and Animals: Focus on Public Health Aspects|
|Number of pages||33|
|ISBN (Print)||9789401794572, 9789401794565|
|Publication status||Published - Jan 1 2015|
ASJC Scopus subject areas
- Immunology and Microbiology(all)