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Fenced pasture: A possible risk factor for human alveolar echinococcosis in Tibetan pastoralist communities of Sichuan, China

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Alveolar echinococcosis, infection caused by the parasitic helminth Echinococcus multilocularis, is a zoonosis strongly linked to climatic and ecological factors. Cross-sectional survey data were used to test a hypothesis that partial fencing of pastures could promote alveolar echinococcosis transmission in semi-nomadic pastoral communities of the Tibetan plateau, PR China. Using multiple stepwise logistic regression with consideration of factors of age and gender, it was shown that partial fencing around the settlements in winter pasture was significantly and independently associated with the risk of human alveolar echinococcosis in the surveyed villages (P = 0.021). The underlying reason may lie in overgrazing, an assumed cause of population outbreaks of small mammal intermediate hosts of the parasite on the Tibetan plateau. Overgrazing may have been exacerbated by the reduction of communal pastures nearby the settlements due to introduction of partial fencing around group tenure pastures acquired by Tibetan pastoralist families.
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... AE forms discrete patches of endemicity within which transmission hot spots of much higher prevalence occur. Promotion of permanent pastures, deforestation, or privatization of the land favors E. multilocularis infection in small mammals and foxes Wang et al. 2004;Pleydell et al. 2004). Involvement of dogs in the life cycle of E. multilocularis, as it occurs in rural western China, and fox urbanization are responsible for higher prevalence of human AE (Torgerson et al. 2011;Vuitton 2003;WHO/OIE and Echinococcosis 2001;Robardet et al. 2011;Deplazes et al. 2004;Romig et al. 2017). ...
Chapter
Cystic echinococcosis (CE) and alveolar echinococcosis (AE) are zoonoses of great medical and veterinary importance, caused by Echinococcus granulosus species complex and E. multilocularis, respectively. The life cycle of these parasites develops between the dog and other canids, which harbor the adult tapeworm in the intestine, and mammal intermediate hosts (including humans as dead-end occasional hosts) where the larval form, the metacestode, develops in different organs.The impact of CE and AE on human health is important, with an estimated 1.2 million people affected and 3.6 million DALYs lost globally for CE and 666,434 DALYs for AE.We describe epidemiology, host’s immune response to parasite, clinical manifestations, diagnosis, and treatment of both CE and AE.
... Fifthly, many types of wild animals with large quantities were reported in the northwest of Sichuan Province, therefore, snow disasters, lack of enough food in spring, and other reasons caused the death of livestock and wild animals. Consequently, this caused the formation of the circulation chain of echinococcosis transmission, thus aggravating the transmission of echinococcosis [46,47]. Sixthly, illiteracy among most residents of Tibetan areas in the northwest of Sichuan Province, with the bad production and living habits including close contact with dogs, feeding sick cattle (sheep) viscera to dogs, not washing hands after eating, and lack of safe drinking water sources, significantly increased the risk of transmission infection [47,48]. ...
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... The historic range and wide distribution of these carnivorous species in Pakistan stretch from the plains in the south to the high mountains further north (Roberts 1997). The correlation between land cover and spatial distribution of AE in humans has been reported in China and France (Giraudoux et al. , 2013aWang et al. 2004Wang et al. , 2006Pleydell et al. 2008). The landscape and favourable environmental conditions have been observed in areas with a higher prevalence of AE cases in humans but the variation among sampling areas (such as villages) remains largely unexplained (Danson et al. 2003(Danson et al. , 2004. ...
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Alveolar echinococcosis (AE) is a zoonosis caused by Echinococcus multilocularis, a heteroxenous parasite belonging to Cestodes. AE is currently considered an important public health issue, but epidemiological and notably molecular data from several endemic countries, including Pakistan, are sparse. Here we report the first detection of Echinococcus multilocularis in wildlife from Pakistan after real-time PCR and sequencing confirmation in the faecal samples of three foxes from northern Kaghan and Siran regions. The apparent occurrence is estimated at 2.9% (95% CI 0.9-12.4). In order to go further in the epidemiological investigations on E. multilocularis and due to the potential presence of other Echinococcus species, we suggest the need for further epidemiological surveys targeting E. multilocularis and E. granulosus sensu lato isolates from humans and intermediate hosts as well as definitive hosts from wildlife in Pakistan.
Chapter
Echinococcus multilocularis is a cestode parasite that circulates in a lifecycle alternating larval and adult forms. The human disease is named alveolar echinococcosis, because of the “alveolar” structure of the parasitic pseudotumor caused by the development of the E. multilocularis larva. In the Jura Massif, under the direction of Pierre Delattre, INRA researchers sampled local small mammal populations from 1979 to 1996 in order to understand the causation of grassland vole outbreaks and their decline phases. The parasite was found in several rodent species over that period. This chapter presents the results obtained over decades in the Jura socioecosystem using this multidisciplinary approach, and examines how this research has been successfully applied to other transmission systems in Asia, mainly in western China and also in southern Kyrgyzstan. Echinococcus multilocularis 's prevalence on a landscape scale rarely exceeds one per thousand in a vole population, even in highly endemic areas.
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What is already known about this topic?: Echinococcosis, also known as hydatid disease, is a zoonotic parasitic disease caused by the larvae of Echinococcus granulosus. Western China has one of the most severe epidemics worldwide. Echinococcosis is endemic in 370 counties of 9 provincial-level administrative divisions (PLADs) including Inner Mongolia, Sichuan, Yunnan, Tibet, Shaanxi, Gansu, Qinghai, Ningxia, Xinjiang and Xinjiang Production and Construction Corps (XPCC). What is added by this report?: From 2017 to 2020, 244 cases were reported in 21 non-endemic PLADs. Of the cases reported in non-endemic PLADs, the majority were imported from endemic areas. Cases reported from non-endemic PLADs have been sporadic, and the number has increased in some areas. What are the implications for public health practice?: Migrant workers and livestock from endemic areas may have contributed to the increased incidence of locally acquired infections in non-endemic PLADs, suggesting that health education among workers and livestock quarantine is important for the control of spread in non-endemic PLADs.
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Echinococcoses are serious zoonotic diseases in China's vast, western and north-western pastoral areas that has one of the highest prevalence in the world. The two most common forms, cystic echinococcosis (CE) and alveolar echinococcosis (AE), are co-epidemic in some areas causing a grave threat to people's health and economic development. Echinococcus spp. are transmitted through domestic, sylvatic and mixed cycles involving many kinds of host. Successful transmission requires a favourable environment for the growth of the parasites and survival of their eggs, while the unique customs and religious beliefs in the endemic areas pose a challenge to the prevention and control of these parasites. Based on previous epidemiological studies, this paper reviews the particular factors affecting the transmission of Echinococcus parasites in China, with a focus on biological (parasite genotype and the species, age, sex and density of hosts), environmental (landscape and climate) and social (age, gender, ethnicity, education, occupation, life style, cultural customs, living conditions and hygiene practices of humans in the endemic areas). These three factors interact with each other and jointly determine the parasites’ transmission intensity, the study of which supports the formulation of the strategies and measures that are significant for control of these infections.
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This review deals with the transmission ecology of Echinococcus multilocularis (Em) in wildlife based on studies carried out in temperate Alaska, China, Hokkaido and eastern France, On a regional scale (n x 10 km), transmission of Em is greater in areas where small mammal densities are regularly high for several months/years. Population dynamics of small mammals respond to landscape changes. Intensive transmission of Em is more likely over landscapes characterised by a poor heterogeneity of habitats, and large areas (percentage) of habitats favourable to cyclic species of susceptible intermediate hosts. Evidence has shown that the functional response of foxes to the density variations of prey populations is to specialise on the species dominant in terms of biomass. Prey/predator relationships are driven by the dominant small mammal species in landscape where rodent outbreaks occur, and as a consequence, the whole system supports intensive transmission of Em. On a local scale (n x 10 m) micro-foci occur in areas where i) fox faeces are scattered at higher densities, ii) Em egg can be protected from early desiccation, and iii) higher intermediate host densities arise. This combination of factors can be reached in different ways that will depend on fox behaviour and on the distribution of the main prey resources, including various seasonal patterns of infection (e.g. eastern France and Hokkaido). The transmission processes of Em strongly depend on the host ecology. A framework for multidisciplinary studies and quasi-experiments on Em transmission can be obtained with comparisons between areas of different levels of endemicity within and between regions, and considering landscape and community processes on different scales. Landscape approaches can potentially allow the development of spatial models in which landscape variables (serving as global variables) integrate the results of community processes. The design of these studies must include a good understanding of the community patterns that may occur on large scales, and of the nested hierarchy of processes linking these scales to local ones where individual infection takes place.