Study On Aedes Aegypti Among Different Strains: Genetic Differentiation And Susceptibility To Dengue 2 Virus With Oral Infection

Objective: In order to understand the role played by the different geographic strains of Aedes aegypti in the spread of DF, and to make preparations for the experiments on the detecting and classification of Aedes aegypti on the molecular level, this paper intends to study the genetic relationships and susceptibility of Aedes aegypti to dengue 2 virus among 4 geographic strains from Hainan, Guangdong, Taiwan of China, and Baro of Indonesia respectively. Methods: Aedes aegypti of different geographic population have been infected dengue 2 virus through oral and indirect Fluoroimmunoassay has been used to detect the infection; RAPD has been used to analyze the DNA polymorphism of Aedes aegypti. UPGMA has been used as cluster analysis for DNA of Aedes aegypti. Results: 1. Susceptibility of different geographic strains to Dengue 2 virus: (1) Using mice-blood-sugar-virus suspension, the infection rate of Baro strain to dengue 2 virus shows significant variation with Hainan strain's and Taiwan strain's (P<0.05) but no significant variation with Guangdong stain's (P>0.05). We observed that with the reduction of virus titre (TCID50), the infection rates of every geographic strain to dengue 2 virus show extraordinarily marked downtrend. When titre (TCID50) of mice-blood-sugar-virus suspension is 2×103.5, the infection rate of Hainan strain is negative. (2) There are no difference in susceptibility of full-blooded femal mosquitos through oral infected dengue 2 virus in mice-blood-sugar-virus suspension and pig-blood-sugar-virus suspension (x2= 1.632, P>0.05). (3) Full-blooding rates of different geographic strains to mice-blood-sugar-virus suspension show significant variation (x2=7.919, P<0.01). The full-blooding rate of Hainan strain (86.7%) is highest and Guangdong strain (79.85%) is lowest. There are no differences in full-blooding rates from pig-blood-sugar-virus suspension (x2==2.586, P>0.05). all of themunder 55%. As to full-blooding rates of different geographic strains to different suspension, the former is obviously higher than the latter (Logistic regression analysis P<0.0001). 2. The genetic variance in different geographic strains of Aedes aegypti: (1) 20 random primers have been chosen for the test. 8 of them could amplify out DNA segments from samples that we selected Aedes aegypti at the same time and show clear. We haven't found that any 2 Aedes aegypti are completely the same of segments. Out of total 113 RAPD bands received, 109 (96.46%) present the polymophism. The numbers of segments applicated by primers are from 6 to 15 and the molecular weight of most segments is from 400 bp to 2000 bp. (2) The inheritic distance between different individuals of the same geographic strain is 0.2212-0.2920, closer than the different geographic strains (0.2920-0.5575). The cluster analysis tested by UPGMA shows that 8 samples can be divided into 4 different groups: Hainan strain, Taiwan strain, Guangdong strain of China and Baro stain of Indonesia. The results are accord with the source of samples. The inheritic distance of Guangdong strain and Baro strain of Indonesia is the closest. Hainan strain is the next closer. Otherwith, the Taiwan strain is relatively independent group. Conclusion: Significant variation exists in susceptibility to Dengue 2 virus in different geographic strains of Aedes aegypti. So the Aedes aegypti in Different natural focus have the different intermediary efficacy. RAPD is an useful method to detected and classify the Aedes aegypti. Through it, the analysis of polymorphic DNA reveals that there have inheritic differentiation in different population of Aedes aegypti.