Natural transovarial transmission of dengue virus 4 in Aedes aegypti from Cuiabá, State of Mato Grosso, Brazil

INTRODUCTION: Dengue is the most prevalent arboviral disease in tropical areas. In Mato Grosso, outbreaks are reported every year, but studies on dengue in this state are scarce. METHODS: Natural transovarial infection of Aedes aegypti by a flavivirus was investigated in the Jardim Industriário neighborhood of Cuiabá, Mato Grosso. Eggs were collected with ovitraps during the dry, intermediate, and rainy seasons of 2012. After the eggs hatched and the larvae developed to adulthood, mosquitoes (n = 758) were identified and allocated to pools of 1-10 specimens according to the collection location, sex, and climatic period. After RNA extraction, multiplex semi-nested RT-PCR was performed to detect the four dengue virus (DENV) serotypes, yellow fever virus, West Nile virus and Saint Louis encephalitis virus. RESULTS: DENV-4 was the only flavivirus detected, and it was found in 8/50 pools (16.0%). Three of the positive pools contained females, and five contained males. Their nucleotide sequences presented 96-100% similarity with DENV-4 genotype II strains from Manaus, Amazonas. The minimum infection rate was 10.5 per 1000 specimens, and the maximum likelihood estimator of the infection rate was 11.6 (95% confidence interval: 4.8; 23.3). CONCLUSIONS: This study provides the first evidence of natural transovarial infection by DENV-4 in Ae. Aegypti in Mato Grosso, suggesting that this type of infection might serve as a mechanism of virus maintenance during interepidemic periods in Cuiabá, a city where dengue epidemics are reported every year. These results emphasize the need for efficient vector population control measures to prevent arbovirus outbreaks in the state.

引言：登革热是热带地区最为流行的虫媒病毒病。在马托格罗索州，每年均有登革热暴发疫情的报道，但针对该州登革热的相关研究却较为匮乏。
方法：本研究于马托格罗索州库亚巴市工业园区社区，针对埃及伊蚊（Aedes aegypti）经黄病毒（flavivirus）自然经卵传播感染的情况展开调查。于2012年旱季、过渡期及雨季，使用诱卵器（ovitraps）采集埃及伊蚊卵。待卵孵化、幼虫发育至成虫后，研究人员对758只蚊虫进行了种类鉴定，并根据采集地点、性别及气候季节将其划分为每组1~10只的混合样本池。完成核糖核酸（RNA）提取后，采用多重半巢式逆转录聚合酶链反应（multiplex semi-nested RT-PCR）检测4种登革热病毒（Dengue virus, DENV）血清型、黄热病毒、西尼罗病毒及圣路易斯脑炎病毒。
结果：本研究仅检测到登革热病毒4型（DENV-4）这一种黄病毒，在50组混合样本池中共有8组呈阳性，阳性率为16.0%。其中3组阳性混合样本池包含雌蚊，其余5组包含雄蚊。其核苷酸序列与来自亚马孙州马瑙斯市的登革热病毒4型Ⅱ基因型毒株的同源性达96%~100%。最小感染率为每1000只蚊虫10.5例，感染率的最大似然估计值为11.6（95%置信区间：4.8；23.3）。
结论：本研究首次证实了马托格罗索州境内埃及伊蚊存在登革热病毒4型的自然经卵传播感染，提示此类感染可能是库亚巴市疫情间歇期病毒维持的一种机制——该市每年均有登革热暴发疫情的报道。本研究结果强调，需采取高效的媒介种群防控措施，以预防该州境内虫媒病毒病的暴发。