2019-2020年塞拉利昂弗里敦市旱季冈比亚按蚊复合体的分子鉴定和传疟作用

Molecular identification and role in malaria transmission of Anopheles gambiae complex in dry season in Freetown,Sierra Leone,2019-2020

目的通过疟疾主要传播媒介冈比亚按蚊复合体在弗里敦市的分布和疟原虫感染率的调查,为制定有效的防疟措施提供流行病学依据。方法2019年12月至2020年3月在塞拉利昂首都弗里敦市10个监测点利用诱蚊灯法进行蚊媒监测研究。将冈比亚按蚊的胸部和腹部分开,分别提取基因组DNA,通过多重PCR鉴定蚊种,利用巢式PCR检测按蚊感染疟原虫的情况,应用Excel 2019和SPSS 21.0软件对结果进行统计分析。结果2019年12月至2020年3月,共捕获按蚊349只,平均诱捕按蚊密度为0.83只/(灯·晚)。西部农村诱捕按蚊324只,占捕蚊总数的92.84%,平均诱捕按蚊密度为2.00只/(灯·晚)。对192只冈比亚按蚊复合体进行的分子鉴定结果显示,冈比亚按蚊(狭义)S-型84只,占43.75%;冈比亚按蚊(狭义)M-型108只,占56.25%。冈比亚按蚊(狭义)中仅检测到恶性疟原虫,未检出间日疟原虫、三日疟原虫和卵形疟原虫。恶性疟子孢子和卵囊阳性率分别为3.13%和6.77%。2019年12月到2020年3月期间的月恶性疟子孢子和卵囊感染率差异无统计学意义。108只冈比亚按蚊(狭义)M-型中子孢子和卵囊阳性率分别为3.70%和7.41%;84只冈比亚按蚊(狭义)S-型中子孢子和卵囊阳性率分别为2.38%和5.95%。冈比亚按蚊(狭义)M-型中子孢子和卵囊阳性率高于S-型,差异无统计学意义。结论弗里敦市的优势按蚊蚊种为冈比亚按蚊(狭义)(M-型和S-型),监测到的其他按蚊有催命按蚊和An.coustani。西部农村按蚊密度远高于西部城区,具有较高的疟疾感染风险。在旱季不同月份,野外诱捕冈比亚按蚊(狭义)的卵囊阳性率均为子孢子阳性率的2倍,而其旱季每月的传疟作用较稳定。本研究将为塞拉利昂疟疾防控策略的制定提供理论依据。

Objective To understand the distribution of Anopheles gambiae complex and its infection rate of Plasmodium in Freetown,Sierra Leone,and provide epidemiological evidence for the effective malaria prevention and control.Methods Malaria vector surveillance was carried out at 10 surveillance sites in Freetown,the capital of Sierra Leone,from December 2019 to March 2020.Genomic DNA was extracted from the thorax and abdomen of each Anopheles gambiae mosquito.Mosquito species were identified by multiplex PCR.The positive rate of Plasmodium in Anopheles was detected by nested PCR.Excel 2019 and SPSS 21.0 were used to analyze the experimental results.Results From December 2019 to March 2020,a total of 349 Anopheles mosquitoes were captured,with an average trapping density of 0.83 Anopheles mosquitoes/trap/night.A total of 324 Anopheles mosquitoes were trapped in the western rural areas,accounting for 92.84%of the total Anopheles mosquitoes captured.The average density was 2.00/night.The molecular identification of 192 An.gambiae complexes showed that 84(43.75%)mosquitoes were An.gambiae s.s.S-form and 108(56.25%)mosquitoes were An.gambiae s.s.M-form.Only Plasmodium falciparum was found in An.gambiae s.s.mosquitoes,but no Plasmodium vivax,Plasmodium malaria,and Plasmodium ovale were found.The positive rates of P.falciparum sporozoites and oocysts were3.13%and 6.77%,respectively.Statistical analysis showed that there was no significant difference in the infection rate of P.falciparum sporozoites and oocysts between December 2019 and March 2020.The positive rates of P.falciparum sporozoites and oocysts of 108 mosquitoes of An.gambiae s.s.M-form were 3.70%and 7.41%,respectively;The positive rates of P.falciparum sporozoites and oocysts of 84 mosquitoes of An.gambiae s.s.S-form were 2.38%and 5.95%,respectively.The positive rates of P.falciparum sporozoites and oocysts of An.gambiae s.s.M-form were higher than those of An.gambiae s.s.S-form,but statistical analysis showed no significant difference.Conclusion The predominant Anopheles species in Freetown was An.gambiae s.s.(M-form and S-form).Anopheles funestus and Anopheles coustani were also found.The density of Anopheles mosquitoes in the western rural areas was much higher than that in the western urban areas,suggesting that the western rural areas has a higher risk of malaria infection.The positive rate of P.falciparum oocysts was two times higher than that of sporozoites in different months in dry season.However,the monthly transmission of malaria was stable in dry season.This study results can be used as theoretical basis for the development of malaria prevention and control strategy in Sierra Leone.