Predictors For The Abundance Of The Wild Small Mammals' Parasitic Fleas In Yulong County Plague Focus

ObjectiveTo know the distribution and proportion of wild small mammals and parasitic fleas in Yulong county plague focus,and to explore the predictors for the abundance of wild small mammals' parasitic fleas,such as the characteristics of the host animals and environmental factors.An epidemiological model will be established to predict the abundance of wild small mammals' parasitic fleas in order to control the occurrence of flea-borne diseases such as plague.Methods1.Study time and sites: From November 2015 to November 2016,an investigation was conducted based on the season in Yulong county plague focus.According to the ecological and geographical landscape,3 altitude areas were selected by using altitude locator.Two to three research samples were selected in each area.2.Collection of small mammals: The snap trap method was used for collecting small mammals.The number of traps of each research sample was not less than 200.The traps were placed for one night.The next day small mammals were bagged back to the laboratory.The small mammals were identified by their external characteristics.Small mammals identified by shape difficultly were taken the skull and identified by relevant experts.The external characteristics,including gender,age,weight,body length,ear length and tail length,were identified and measured.3.Collection of parasitic fleas: The parasitic fleas of small mammals were collected by comb method and stored in a 75% ethanol-containing cryogenic tubeunder room temperature.According to "Yunnan fleas",the fleas were identified and counted under a microscope.4.Collection of environmental factors: The altitude of each research sample was recorded by the altitude locator;habitat types were determinate by investigation;the temperature and humidity of the day were measured by instrument.5.Data collection and analysis: A database was created using EpiData software,the relationship between the abundance of parasitic fleas and the potential predictors was explored,using hurdle negative binomial regression model under R software,statistical packages included epicalc,pscl,and lmtest.The number of parasitic fleas of each small mammal was regarded as dependent variable and the factors affecting the abundance of parasitic fleas such characteristics of small mammals and environmental factors were regarded as the independent variables.Due to the distribution of parasitic fleas on small mammals were scattered,hurdle negative binomial regression model was applied to explore the relationship between the abundance of parasitic fleas and the predictors.Firstly,univariate analysis for each variable was conducted and the variables with p value less than 0.15 were chosed to enter the prototype multiple regression model as candidate variables.Likelihood ratio test(LR-test)was used to compare the degree of fit of different models,the final model was refined using backward regression to reduce independent variables(?=0.10 as statistical significance level).Results1.A total of eight hundred eighty four small mammals were caught in Yulong plague focus and were divided into 18 species,12 genera,5 families,3 orders.Of 884 small mammals,the number of Apodemus chevrieri was 309(34.95%);Apodemus draco was 159(17.99%);Eothenomys miletus was 142(16.06%);Apodemus latronum was 104(11.76%);Eothenmys proditor was 58(6.56%);Niviventer confucianus was42(4.75%);Tupaia belangeri was 23(2.6%);Dremomys pemyi was 20(2.26%);the number of other small mammals was 27(3.05%).Apodemus chevrieri ?Apodemus draco?Eothenomys miletus and Apodemus latronum were the dominant species.2.There were 484 parasitic fleas from small mammals captured in Yulong plague focus and were divided into 9 species,7 genera,6 subfamilies and 3 families.Of 484 parasitic fleas,the number of Neopsylla specialis specialis was 165(34.09%);Ctenophthalmus quadratus was 123(25.41%);Macrostylophora euteles was70(14.46%);Ctenophthalmus yunnanus was 59(12.19%);Frontopsylla spadix spadix was 45(9.3%);the number of other fleas was 22(4.56%).Neopsylla specialis specialis?Ctenophthalmus quadratus?Macrostylophora euteles and Ctenophthalmus yunnanus were the dominant species.3.Rodent species,age,body length,altitude,season,temperature and humidity were related to the abundance of the parasitic fleas of the wild small mammals in Yulong plague focus.Compared with Apodemus chevrieri,the probability of flea infestation on Apodemus draco reduced by 50%,while the probability of flea infestation on Eothenomys miletus increased by 0.79 times.The number of fleas on adult small mammals increased by 2.25 times.The probability of flea infestation on small mammals with body length exceeded 104 mm increased by 0.76 times.The probability of flea infestation 2700-3000 m and above 3000 m increased by 1.27 times and 3.72 times more than that of 2400-2700 m,respectively.Compared with spring,the number of fleas in summer increased by 2 times,the probability of flea infestation in autumn decreased by 48%,the probability of flea infestation and the number of fleas in winter increased by 1.44 times and 1.06 times respectively.When the temperature exceeded 15 ?,the number of fleas on small mammals decreased by67%.The probability of flea infestation decreased by 41% when the humidity was over 70%.Conclusions1.There were 18 species,12 genera,5 families,3 orders of small mammals in Yulong plague focus,with Apodemus chevrieri ? Apodemus draco ? Eothenomys miletus and Apodemus latronum as the dominant species.The distribution of the species along the altitudes is different,Eothenmys proditor was only caught above3000 m,which was the common species,and its probability of flea infestation and theindex of fleas were all high.2.There were 9 species,7 genera,6 subfamilies,3 families of parasitic fleas of the Yulong plague focus,with Neopsylla specialis specialis ? Ctenophthalmus quadratus?Macrostylophora euteles and Ctenophthalmus yunnanus as the dominant species.3.Rodent species,age,body length,altitude,season,temperature and humidity were related to the abundance of parasitic fleas of wild small mammals in Yulong plague focus.The probability of flea infestation on Apodemus chevrieri was higher than Apodemus draco and was less than Eothenomys miletus.The number of fleas on adult small mammals increased.The probability of flea infestation increased on small mammals with body length over 104 mm.With elevation increasing,the number of fleas increased.Compared with spring,the probability of flea infestation in autumn decreased,and the probability of flea infestation in winter increased;the number of flea infestation in both summer and winter.The number of fleas decreased with temperature over 15 ?.The probability of flea infestation reduced with humidity over 70%.