Influences On The Natural Focus Diseases At The Reservoir Area Of Three-Gorge Project

ObjectiveThis subject is to study three-gorge project's influence on the diseases prevalence in the reservoir areas after 3rd phase water storage through Field Epidemiology And Seroepidemiology investigation, provide the evidence to institute the prevention and cure strategy of Natural foci of the disease, predict environmental medicine problems which will occur in the near future, and draw off the strategy.Methods1. To draw four natural countrysides from Mao Ping Town and Tai Pingxi Town of ChangJiang river′s upstream and San Douping Town , Le Tianxi Town downstream as our investigation point by random, these point had streams or water returning. We had organized four investigations in these four towns in May and September in 2006 and 2007. Mice density and species were investigated with night clip-trip, while we collected the data of the annual disease surveillance and diseases in Three Gorges as comparison.2. We collected 161 mice lung specimens at the dam area, then stored them in the liquid nitrogen canister for determination. EHF virus antigen of hosts were detected by the direct immunofluorescent assay technique(DIFA). We collected the correlated data at the area of reservoirs, and used the SPSS13.0 statistical package to undertake dependability test. Sera EHFV-IgG antibody of the healthy people was detected by the enzyme-linked immunosorbent assay(ELISA). 3. Field epidemiological survey and seroepidemiological study were performed. Serum IgG antibodies against paragonimus of the crowd were detected by enzyme-linked immunosorbent assay (ELISA), and questionnaire investigation was carried out simultaneously. Epidemiological survey was performed on the density and constitution of crabs. Metacercaria was detected in freshwater crabs by anatomical lens and the infective rate was calculated. The data was analyzed by Excel software, and SPSS13.0 statistics software was used to calculate the infective rate, constitutive ratio, Chi-square test,and correlation analysis, probabilities.4.We obtained the diseases'epidemical data over the years of Tai Pingxi Town, San Douping Town, Le Tianxi Town and Mao Ping Town from relative department, then analyzed and gathered them. Tai Pingxi Town and Mao Ping Town lie on the left and right hand of the dam upstream; Le Tianxi Town and San Douping Town lie on the left and right hand of the dam downstream, while Deng country is away from the dam area.Results1. The average mice density was 10.88% in 2007, mice density of two months was 10.03%,11.71%, they had no significant difference. Mice density of the indoor was significantly higher than the outdoor. Mice density of the downstream was higher than the upstream. Mice density of 2007 is much higher than 2006. Basic on the analysis of the collected data, we had found that the mice density in 2002 that one year before the water-retention was significant lower than in 2004 that one year after the water-retention., but the mice density was raised against in 2005 that two years after the water-retention. The analysis of the influence factors on mice density, we had found that there was no dependability between the weather factors and the areas of the farmland with the mice density over the years in the reservoir, the two factors were not the major effective factors of the mice density change.2. The infective rate of mice with EHF virus was 9.32%. The infective rate indoor was more serious than outdoor. The infection sources in the dam area were Soul type. There was no difference in the infective rate of mice among the four investigation points. There was no difference in the infective rate between the upstream and the downstream. Basic on the collected data, we found that the infective rate in the reservoir maintained at a relatively low level, though it appeared a small peak every 4~5 years. The infective rate dropped to the lowest level(0%) in the history in 2003 when it started to store water, but the rate raised against one year later. The infective rate in the dam area(9.32%) was higher than the level in the whole reservoir before 2006. Correlation test was used to tested the infective rate between the indoor and outdoor separately, and we found statistic significance in positive correlation between them.3. In order to determine previous exposure to paragonimiasis among the local residents, Paragonimiasis IgG antibody of serum samples from 398 inhabitants were examined using ELISA test. Three male samples showed positive and the rate was 0.748%. The ages of three positive children are 12 year-old, 12 year-old, and 14 year-old boys respectively. A common characteristic of them was that they did not eat raw crabs, but drank raw water. Paragonimus IgG antibody showed positive from serum samples in Letianxi town, but negative in the other three towns. In this survey, Paragonimiasis cases with typical symptoms and physical signs were not found. Questionnaire investigation indicated that consumption of raw or inadequately cooked crabs was 1.6%, but the universal behavior of drinking raw water was 58.4%.4. Dysentery and malaria were frequent diseases in the Three-gorge dam area, the incidence rate of other diseases were all at a little lower level,. There is not obvious difference in the incidence rate of all communicable diseases in all districts.Conclusions1. Compared with the consequence during the water storing, the mice density at the dam area had raised, and the density was at a little higher level. Compared with 2006's result, the mice density in 2007 had obviously increased, which indicated us to make some measures to kill mice adequately to prevent mice'related diseases, and the density in upper dam area was higher than down dam area. We also found that the mice had shifted from outdoor to indoor.2. There was no EHF case in the dam area, unapparent infection among the healthy people was also lower than that in the whole reservoir. The dam area was considered as latent epidemic area of EHF. The change of the ecological environment had never influenced the EHF after the water–retention, but we should strengthen epidemic prevention and sine die overall deratization to prevent the incidence rate of EHF from rising or breaking out.3. This epidemiology study result showed that the dam region is still a medium natural epidemic focus of paragonimiasis. The Three Gorges has been constructed for 12 years, but epidemic and intermediary infection drop. It does not have obvious effects on Paragonimiasis. At present, the infection situation of people and intermediary host are on balanced state with stepwise decline. Paragonimiasis is a zoonotic disease. Although infection of people in the part of region have already controlled, as long as natural foci exist, paragonimus would cause new epidemic.4. We could not get a conclusion that Three-gorge dam would lead to the outbreak of all kinds of Natural focus infection diseases. If epidemic focus and suitable conditions of prevalence exists, a large scale of epidemic diseases would happen possibly, so we should keep on a vigilance state, and made all kinds of prevention and control measures.