Study On The Susceptibility Of Anopheles Sinensis And Anopheles Anthropophagus To Plasmodium Vivax

Malaria is one of the three epidemic diseases in the program of United Nations (U.N)'prevention and control for Millennium Development Goals (MDGs). Malaria, AIDS (Acquired Immure Deficiency Syndrome) and TB (tuberculosis) are three urgent public health problems in the world. Among the four species of parasite infected to human, Plasmodium vivax and Plasmodium facliparm are the most abroad distribution in the world. Plasmodium vivax has the lower pathogenicity than plasmodium facliparm. However, due to its relapse and more abroad distribution in the world, vivax malaria control is even more difficult than plasmodium facliparm. In recent years, vivax malaria reemergence and outbreak occurred in central part of China.Anopheles sinensis (An.s) and Anopheles anthropophagus (An.a) are the major malaria vectors and have the most abroad distribution in China. Both of them have been confirmed as the major vivax malaria vectors for plasmodium vivax transmission in China. So, the study of susceptibility to plasmodium vivax of An.s and An.a and the evaluation of the vectors capacity as well as the transmissiom ability of An.s and An.a are the one of the hotspots for malaria research in China. The method to directly measure the susceptibility of mosquitoes to parasites is the laboratory parasites infection to mosquitoes, of which the most extensive application is the mosquito artificial membrane feeding in vitro. The objective of this subject is to compare the susceptibility of the An.s and An.a, the major malaria vectors in China, to Plasmodium Vivax and to evaluate their effect in malaria transmission in vivax malaria epidemic areas in central part of China. The study includes three parts:Part I: The establishment of the laboratory in vitro artificial membrane blood- feeding systemObjective:To establish a new laboratory in vitro membrane feeding system for the vectors susceptibility study in China by improving the membrane feeding facilities and methodsMethod: The new membrane feeding equipments have been used for An.a Jiangsu strain in vitro membrane feeding to compare and analysis the factors affect to mosquitoes blood feeding resultResult:I. There was no significant difference in blood engorged mosquitoes'rate between the mosquitoes'age 3-8days after eclosion. So, 3-4days age of mosquitoes was better than 5-8 days age of mosquitoes for susceptibility study because of the longevity of infected mosquitoes.II. Although there was the difference in blood engorged mosquitoes'rate between the starvation time: 8-24hs and more than 24hs, the 8-12 hs'starvation time was more suitable for susceptibility study according to the correlation of the blood feeding rate and mortality of the mosquitoes.III. The daytime engorged mosquitoes'rate was higher than that in the evening. However, there was no difference between black cloth cover and without cover during the feeding period in the daytime. The size of mosquito cage had no effect to the result.Part II: Study on the susceptibility of An. sinensis and An. anthropophagus to Plasmodium vivaxObjective: To study the susceptibility of An.s and An.a to Plasmodium vivax by using the new established laboratory in vitro artificial mosquito feeding system.Method: Both of laboratory Jiangsu strain and field strain of An.s and An.a from Jiangsu, Liaoning, Guangdong (Zhuhai) were fed on the blood samples of the vivax malaria patients in the epidemic areas of central part of China by using the new established laboratory in vitro artificial mosquito feeding system.Result:I. 10 blood samples of vivax malaria cases have been fed with both of laboratory Jiangsu strain and field strain of An.s at the same time. The results shown that there was no significant difference between the laboratory colony and field strain of An.s .II. 142 blood samples of vivax malaria cases were paralleled fed with laboratory strains of An.s and An.a. There were no significant difference in oocyst, sporozoite positive rate and the ratio of positive mosquitoes between laboratory strains of An.s and An.a. Although the oocyst lever of An.s was higher than An.a, there was no significant difference in sporozoite lever between laboratory strains of An.s and An.a.III. 35 blood samples of vivax malaria cases were paralleled fed with An.a of Jiangsu, Guangdong and Liaoning laboratory strains. There was no significant difference in oocyst and sporozoite infective rate and the ratio of positive mosquitoes among these 3 laboratory strains.Part III: The analysis of the Influence factors of plasmodium vivax growth in the mosquitoes.Objective: To compare the factors to influence mosquito in vitro infection with plasmodium vivax in the lab.Method: the susceptibility of the An.s and An.a to fever and non-fever stage plasmodium vivax have been Compared respectively. The correlation of gametocyte density and sexual ratio with oocyst and sporozoite of An.s and An.a have been analysed and the relationship between oocyst and sporozoite of An.s and An.a have been estimated。Result:I. The rate of oocyst and sporozoite, the ratio of sporozoite positive mosquitoes and the degree of sporozoite of An.s to non-fever stage plasmodium vivax were higher than fever stage plasmodium vivax.II. The rate of sporozoite as well as the ratio of oocyst and sporozoite positive mosquitoes of An.a to non-fever stage plasmodium vivax was higher than fever stage plasmodium vivax. III. The oocyst and sporozoite rate as well as their degree of An.s and An.a were correlated with the gametocyte density. However, they have no correlation with sexual ratio of gametocyte.IV. It has been found that the more oocyst degree appeared, the more sporozoite rate and degree in both An.s and An.a .Conclusion:1. The new established laboratory in vitro artificial membrane blood feeding system is suitible for malaria vectors susceptibility experiment in China. The new system has obvious improvement on the standardization of in vitro artificial membrane blood feeding operation in the lab. So it had a good foundation to analyse the results of malaria vectors susceptibility experiment in different labs.2. The lab strain of An.s can be substituted by field F1 strain for susceptibility study of An.s to plasmodium vivax.3. The new found An.a from Liaoning and Guangdong (Zhuhai) are susceptible to plasmodium vivax and the susceptibility of them had no difference with An.a in central part of China.4. It has been found that the susceptibility of An.s was similar as An.a to plasmodium vivax in the epidemic areas of central part of China. The results indicated that the further study of An.s susceptibility to different genotypes of Plasmodium vivax is needed for malaria control in the epidemic areas with the An.s prevalence. 5. The blood samples collected from different fever stage, the gametocyte density had definite correlation with mosquitoes'oocyst and sporozoite infective rate and degree, however the sexual ratio of gametocyte had nothing on that in laboratory in vitro artificial membrane feeding test.Innovative point:1. Established a new in vitro artificial membrane blood feeding system Which is suitible for lab malaria vectors susceptibility operation in China.2. It is first time to confirm that the new found An.a from Liaoning and Guangdong (Zhuhai) are susceptible to plasmodium vivax and the susceptibility of them had no difference with An.a in central part of China in the lab.3. It is first time to find that the susceptibility of An.s is similar as An.a to plasmodium vivax in the epidemic areas of central part of China.