It thus appears that, in the Tibetan communities, the transmission cycle of E.multilocularis is functioning well. However, few researches tried to explore the socio-economical and behavior risk factors for AE/E.multilocularis transmission in the Tibetan region.
Geographic, demographic, climatic, socio-economical and behavioral particularities of Sichuan Province, PR China, and their
Geography, demography and climate of Sichuan province, PR China
In the southeast part of the prefecture, the landscape is mainly high mountain valley; in the middle part of the prefecture it features with altitude plain and in the northwest part it features with plateau. The area of the prefecture is 153 thousand km2, which is the biggest one among administrative areas of the same level in the province (See Figure I-1, Chinese administrative region institutional structures), accounting for 1/3 of the area of Sichuan Province.
Socio-economical and behavioral characteristics of the Tibetan communities
Hui (Muslim) people are usually invited to do the job (Shiqu County Editorial Committee for Shiqu County Record, 2000; Rangtang County Editorial Committee for Ganzi County Record, 1997;. Yak number is more important than yak health (Shiqu County Editorial Committee for Shiqu County Record, 2000; Rangtang County Editorial Committee for Ganzi County Record, 1997; Hongyuan County Editorial .. Committee for Hongyuan County Record, 1996; Ruo’ergai County Editorial Committee for Ruo’ergai County Record, 1996).
Risk factors of human AE transmission in the Tibetan communities
We thus addressed the epidemiology characteristics and especially the specific risk factors for each population in two counties of the Sichuan Tibetan plateau in order to better understand the mode of transmission of E. By the end of 1997, there was an estimated livestock population of 326,730 of the same species as in Shiqu county. The studies were approved by the Ethical Committee of Sichuan Institute of Parasitic Diseases, Sichuan Province as well as those of collaborating investigators, according to the regulation operating for the NIH of the USA.
Finally, single factor and multiple factor stepwise logistic regressions were employed to identify risk factors fo each of the three populations.
AE prevalence according to gender and age
Risk factors for herdsmen, farmers and urban communities
After multiple factors stepwise logistic regression, only county of residence (Shiqu County vs. Ganzi County, p=0.009, OR=5.167) and age (p=0.001, OR=1.078) were found to be statistically significant risk factors. Therefore, co linearity might exist between county of residence and fox skin products ownership as well as between county of residence and number of dogs kept. There was co-linearity between the county of residence and the number of dogs kept on one hand, and between the county of residence and ownership of fox skin products on the other hand.
A canine purgation study and risk factor analysis for echinococcosis in a high endemic region of the Tibetan plateau.
History and current management of grazing practices Guiding questions: 1) What is overgrazing? 2) How can we measure it? 3) What is the
Definition of overgrazing and origin of overgrazing
Li (1995) stated that the productivity of pastures decreased dramatically and the number of livestock kept decreasing from 1,050 thousands in 1980 to 770 thousands in 1993, because of the invasion of small mammals to pastures and overgrazing. Overgrazing is used as the canonical example of the so-called "Tragedy of the commons". The tragedy of the commons is a metaphor that illustrates the sub-optimal use or even destruction of public resources (the "commons") by private.
Since the herdsman receives all the proceeds from the sale of the additional animal, the positive utility is nearly +1.
Property rights and grazing practices: history and current aspects
However, in his paper, Cox did not mention if the pastures were scarce resource or not when commons worked well. When distributing pasture use rights and resolving dispute on use rights of pastures, the head of tribe needed to summon some people concerned to discuss, which indicates that at that time the head did not think the pastures belonged to himself. Generally, the permanent pastures were never private properties, because if the tribe could find any proper reason, for example, when the number of livestock of a family decreased, part of the pastures used by the family could be distributed to other families with more livestock.
Especially when the pastures are actually commons, it is very hard to imagine that people can.
Socio-economical correlates of overgrazing
In the middle of the 1980s, in response to increasing conflicts over pastures use rights and the deterioration of pastures and to promote good neighborhood, a new law (Chinese Pasture Law) was issued to ask for defining the boundary among counties, among townships, and among villages. The new law also stated that one household or a group of households (group tenure) were being responsible for contracting with government for use rights of pastures. Rangtang County Editorial Commission for country record, 1997; Ruo’ergai County Editorial Commission for country record, 1996; Hongyuan County Editorial Commission for county record, 1996.
Rangtang County Editorial Commission for country record, 1997; Ruo’ergai County Editorial Commission for country record, 1996; Hongyuan County Editorial.
Grazing practice as a potential risk factor for E.multilocularis transmission
Interaction between grazing practice and small mammal populations around
National Engineering Laboratory site" (INEL site), researches were done to understand the grazing effects on the abundance of small mammals. Some found that grazing led to lower abundance and species of small mammals (Reynolds and Trost 1980). By contrast, in several other studies, populations and/or species of small mammals were reported to increase on grazed sites.
Therefore, it seems that a correct assessment of the relationship between overgrazing and abundance of small mammals is still missing internationally.
Interaction between grazing practice and small mammal populations in
One of the papers claimed to have the purpose to link overgrazing and small mammals in its title, but it actually studied relationship between grazing and small mammals (Wada et al.1995). Conversely, however, some believed that it was overgrazing that contributed to pastures degradation then to the outbreak of small mammals (Li, 1995; Hou, 2001). Some believed that overgrazing had direct relationship with outbreak of small mammals, namely, overgrazing leading to pasture degradation then leading to small mammals invasion, then pastures further overgrazed by small mammals, then the pastures further degraded (Li, 1995; Hou, 2000).
It was calculated that in Qinghai Province, the forage consumed by small mammals averaged 41.1 billion kilograms a year (Hou,.
Partial fencing and AE prevalence in the Tibetan herdsmen communities
Echinococcosis is a major public health problem in western Sichuan Province, PR China, especially in the pastoral communities of the Tibetan plateau (Schantz. The estimated fenced area in each village was the prod- uct of the number of bundles of pen and the area of pasture that one bundle of pen can fence. AE is a chronic infection with a long asymptomatic stage, and its progression varies according to the individual immune response of the host (Vuitton et al., 2002).
Open landscapes with humid soil were suggested to be favorable for the life cycle of the parasite (Staubach et al., 2001).
Overgrazing and AE/E.multilocularis transmission
The median density of small mammal burrows in open pastures was independently associated with dog E.multilocularis infection (p=0.003, OR=1.048). Data related to livestock management, perception of the gap between the forage needs of livestock and the production capacity of the pastures, the density of small mammal burrows, the area of fenced pastures and prevalence of dog infection in settlements were used in the analysis. The density of small mammal burrows outside fenced areas was compared with that within the fenced areas using non-parametric tests considering landscape factor.
Multiple stepwise logistic regression was used to relate median density of small mammal burrows to dog infection in the settlements.
Livestock management
Characteristics of the settlements
The enumeration of small mammal burrows based on 1,500 observations was done along the 30 km of transect. Multiple forward conditional stepwise logistic regressions showed that the median density of small mammal burrows in the open pastures was significantly positively related to dog infection (p=0.003, OR=1.048) (table 3). Comparisons of densities of small mammal burrows in open pastures with these in fenced pastures stratified by landscapes (Density: number of burrows per 200 . m2 of pasture) No.
Relationship between surface of fenced pastures and densities of small mammal burrows in the open pastures in the settlements (Spearman correlations).
General discussion
Summary of the results
However, in addition, a direct role for foxes in E.multilocularis transmission to humans was pointed out for the first time in China by our epidemiological study. The median density of small mammal burrows in open pastures was revealed to be independently associated with dog infection by E.multilocularis (p=0.003, OR=1.048) by a multiple stepwise logistic regression analysis considering dog sex and age as well as the type of measurement of dog infection. This observation, on the Tibetan plateau further confirmed that dogs might play an important role in AE/E.multilocularis transmission as was also found in other Chinese provinces such as Gansu (Craig et al, 2000).
In addition, dogs were found to play a role in E.multilocularis transmission to human by risk factors analyses.
Evaluation and/or measurement of overgrazing: difficulties and debates
The following general discussion will especially deal with the methodological issue of the definition and measurement of overgrazing, and will try to give a synthetic view of the interference between intrinsic, environmental and behavioral factors in the occurrence of AE in a given region/community, with special reference to the Tibetan plateau. changes in pika density might not be the outcome of overgrazing, but of temperature and humidity changes, and could even be the reason for vegetation changes and thus. Therefore, because of this somehow "vicious circle", it seemed that ecological indicators or livestock husbandry indicators were not readily applicable to our research. After checking available possibilities, we turned to socio-economics indicators that seemed to be more reliable given the socio-economics origin of overgrazing.
Through the definition of overgrazing in terms of socio-economics paradigm, two indicators were adopted to verify the existence of overgrazing: 1) scarcity of pastures and 2) common ownership of pastures.
Small mammal communities and their role as reservoir of E. multilocularis
The population density of small mammals seems to be one of the key factors for the transmission of E.multilocularis: high densities were found quantitatively associated with infection of foxes and with the prevalence of AE in humans in France and Gansu Province, China (Viel et al., 1999; Craig et al., 2000; Giraudoux et al 2002;. In Tibetan pastures, the situation of small mammals is far from clear in terms of all above 3 factors listed above. From data obtained by field trapping of small mammals, visual observation and literature review, 18 species of small mammals belonging to 10 genera have been described in the area we worked in.
Not all species of small mammals are fully identified, their distribution patterns and densities were not studied systematically, and their susceptibilities to E.
Environmental, intrinsic and behavioral factors for AE transmission
In Switzerland, high prevalence of E.multilocularis in domestic animals (dogs and cats) seemed not to be associated with a higher clinical AE incidence in humans living in the same region (Bruno et al., 2001). However, high prevalence of E.multilocularis in wild (Arvicola terrestris and Microtus arvalis) seemed not to be associated with a higher prevalence of AE in humans living in the same region (Bruno et al., 2001). Culture in the Tibetan communities is also very conducive to the existence of large number of dogs.
The number of dogs in the Tibetan communities actually depends on the availability of food.
Open questions
The distribution of data on small mammals was detected as extremely far from normal distribution. If overgrazing in winter pastures around the settlements contributes to abundance of small mammals that may in turn promote transmission of AE, further understanding of the overall overgrazing situation in both winter pastures and more extensive summer pastures should also be obtained since the Tibetan families live in both environments. However, overgrazing is also present in summer pastures and high densities of small mammals were also observed, and contamination of humans in summer pastures cannot be ruled out totally.
This should also be associated with a quantitative direct assessment of small mammal species in the various habitants, which requires systematic trapping and identification in the same areas.
Conclusion and perspectives
This may be done based on a direct measurement of overgrazing which asks for a methodology development of quantification of overgrazing. This should also be associated with a quantitative direct assessment of small mammal species in the various habitants, which requires systematic trapping and identification in the same areas. fencing of pastures in winter settlements and AE prevalence in the studied community. Consequently, there could be continued and sustained overgrazing, which might lead to continuously increasing abundance of small mammals, both in common and fenced pastures, conducive to increasing transmission of AE before the pastures totally destroyed which makes the land not suitable for the survival of livestock as well as humans…In Mengge 1 village and Mengge 2 village, Mengyi Township, Shiqu County, the number of livestock kept per . people) had no longer livestock at all; and 95% of pastures in the two villages had become what is usually called "black beaches" (rodent wasteland) (Li, 1995).
Another prospective direction could also add knowledge to the issue of overgrazing and transmission of AE/E.multilocularis.