| ObjectiveTo understand the changes of entironment in Three Gorges dam after sluice, especially the changes of the environment for rodents'inhabitating and surviving, the changes of local inhabitants' and immigrants' living and producing environment, and as natural host for EHF virus, rodents' population distribution and virus-taking status. So as to provide references for disease control and prevention of the population in Three Gorges, and supply evidences for public health strategies in the area.MethodTo introduce the method that combines locale epidemiology and laboratory inspection. In locale epidemiology, selecting randomly two villages in the upper and two ones in the downstream as survey plots. There were two times, in May and September 2007, to investigate rodents' density and its cluster distribution with the method of trap-night. Then, to anatomise mice we catched asepticly to get the lung samples and blood ones. The samples we collected were all stored in fluid-nitrogen kettle, so as to get back to the lab to detect EHF-virus antigen with the method of direct immunofluorescence and EHF-virus antibody with means of indirect immunofluorescence.ResultThere set 2914 trap-nights overall the year, and 317 specimens were trapped. The rodent density was 10.88%. In 1445 trap-nights in May, 145 specimens were trapped, and the density was 10.03%. And in 1469 trap-nights in September, 172 specimens were trapped, and the density was 11.71%. The difference between the two above was nonsignificant(χ~2=2.11,p=0.147). In the year, the mouse density indoor and outdoor were separately 16.70% and 5.12%. And the difference between them was significant(χ~2=100.79,p<0.001). In the upper of Three Gorges Dam, the rodent density was 13.06% the whole year and at the same time, the density in the downstream was 10.51%. The difference between them is significant (χ~2=8.21, p<0.05). The rodent density of this year had obviously increased, compared to last year.The result of the survey of rodent population in the dam showed that, Rattus tanezumi(28.39%) was the dominant species in all trapped specimens of the four investigation plots. And the following were Mus musculus(21.77%), Rattus losea (18.30%), Apodemus agrarius(17.67%) and Rattus norvegicus(10.73%), etc. Over the year, in the upper of Three Gorges Dam, the dominant species was Rattus tanezumi(28.24%), and the following were Apodemus agrarius(26.47%), Mus musculus (20.00%) and Rattus losea(14.71%). Correspondingly, in the downstream, the dominant species was still Rattus tanezumi(28.57%), and then was followed by Mus musculus(23.81%), Rattus losea(22.45%) and Rattus norvegicus(14.29%). The comparability of rodent populations outdoor in the downstream in May and September was low(similarity coefficient was 0.50), which showed that there exsited differences in the constitute of rodent populations outdoor between in May and September.Altogether, we collected 161 lung samples and 184 blood filter paper samples of rodents. The method of direct immunofluorescence was used to detect EHF-virus antigen of the lung samples, and we found 15 positive ones. The positive ratio was 9.32%. The method of indirect immunofluorescence was used to detect the EHF-virus antibody of the blood samples, and 6 positive ones. The positive ratio was 3.26%. In all lung samples of rodents, the species which had the highese virus-taking ratio was Mus musculus(13.79%), the following were Rattus losea(12.00%), Rattus tanezumi(8.51%) and Apodemus agrarius(6.25%). While in all blood samples of rodents, the highest virus-infection ratio species was Rattus losea(5.88%), which was followed by Rattus norvegicus(4.00%) and Apodemus agrarius(2.86%). ConclusionThe rodent density had increased rapidly during the third-phase sluice period in Three Gorges Dam. Compared with past construction years of Three Gorges project, the amplitude was greater. And the rodents' EHF virus-taking ratio had also increased by some degrees. According to the two times of epidemiology survey this year, we could get that with the increasement of rodent density and virus-taking ratio in Three Gorges Dam, EHF would make threaten to the people's health in the dam area. Otherwise, since the rise of the water lever in reservior area, antinomy between man and land would get worse, and inhabitating density of the immigrants would increase, all conditions above would promote the epidemic of EHF in population. As a result, the relevant departments should make measures in time to perish and control rodent populations which was EHF-virus natural foci host. Besides that, immunity inoculation to high-risk population such as young farmers should be enhanced, so as to eliminate the public health influence which was resulted in by the construction of Three Gorges Dam as completely as possible.
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