National Mosquito-Borne Diseases Control Research Center, National Health Research Institutes, Miaoli County, Taiwan.
Institute of Advanced Research, Nagoya University, Nagoya, Japan.
Parasit Vectors. 2022 Apr 21;15(1):137. doi: 10.1186/s13071-022-05276-w.
The primary disease vectors for dengue virus (DENV) transmission between humans are the mosquitoes Aedes aegypti and Aedes albopictus, with Ae. aegypti population size strongly correlated with DENV outbreaks. When a mosquito is infected with DENV, the virus migrates from the midgut to the salivary glands to complete the transmission cycle. How the virus crosses the hemocoel, resulting in systemic infection, is still unclear however. During viral infection and migration, the innate immune system is activated in defense. As part of cellular-mediated immunity, hemocytes are known to defend against bacteria and Plasmodium infection and may also participate in defending against DENV infection. Hemocytes are categorized into three cell types: prohemocytes, granulocytes, and oenocytoids. Here, we investigated which hemocytes can be infected by DENV and compare hemocyte infection between Ae. aegypti and Ae. albopictus.
Hemocytes were collected from Ae. aegypti and Ae. albopictus mosquitoes that were intrathoracically infected with DENV2-GFP. The collected hemocytes were then identified via Giemsa staining and examined microscopically for morphological differences and viral infection.
All three types of hemocytes were infected by DENV, though the predominantly infected cell type was prohemocytes. In Ae. aegypti, the highest and lowest infection rates at 7 days post infection occurred in prohemocytes and granulocytes, respectively. Prohemocytes were also the primary infection target of DENV in Ae. albopictus, with similar infection rates across the other two hemocyte groups. The ratios of hemocyte composition did not differ significantly between non-infected and infected mosquitoes for either species.
In this study, we showed that prohemocytes were the major type of hemocyte infected by DENV in both Ae. aegypti and Ae. albopictus. The infection rate of prohemocytes in Ae. albopictus was lower than that in Ae. aegypti, which may explain why systemic DENV infection in Ae. albopictus is less efficient than in Ae. aegypti and why Ae. albopictus is less correlated to dengue fever outbreaks. Future work in understanding the mechanisms behind these phenomena may help reduce arbovirus infection prevalence.
登革热病毒（DENV）在人与人之间传播的主要病媒是埃及伊蚊和白纹伊蚊，埃及伊蚊种群数量与 DENV 爆发密切相关。当蚊子感染 DENV 时，病毒从中肠迁移到唾液腺以完成传播周期。然而，病毒如何穿过血腔导致全身感染尚不清楚。在病毒感染和迁移过程中，先天免疫系统被激活以进行防御。作为细胞介导免疫的一部分，血淋巴细胞已知可抵抗细菌和疟原虫感染，也可能参与抵抗 DENV 感染。血淋巴细胞分为三种细胞类型：原血细胞、粒细胞和浆血细胞。在这里，我们研究了哪些血淋巴细胞可以被 DENV 感染，并比较了埃及伊蚊和白纹伊蚊的血淋巴细胞感染。
通过胸部内感染 DENV2-GFP 的埃及伊蚊和白纹伊蚊收集血淋巴细胞。收集的血淋巴细胞通过吉姆萨染色进行鉴定，并通过显微镜检查观察形态差异和病毒感染。
所有三种类型的血淋巴细胞都被 DENV 感染，但主要感染的细胞类型是原血细胞。在埃及伊蚊中，感染后 7 天的最高和最低感染率分别发生在原血细胞和粒细胞中。原血细胞也是 DENV 在白纹伊蚊中的主要感染靶标，其他两种血细胞群的感染率相似。在这两个物种中，非感染和感染蚊子之间的血淋巴细胞组成比例没有显著差异。
在这项研究中，我们表明原血细胞是埃及伊蚊和白纹伊蚊中 DENV 主要感染的血淋巴细胞类型。白纹伊蚊中原血细胞的感染率低于埃及伊蚊，这可能解释了为什么白纹伊蚊中系统性 DENV 感染效率低于埃及伊蚊，以及为什么白纹伊蚊与登革热爆发的相关性较低。未来在理解这些现象背后的机制方面的工作可能有助于降低虫媒病毒感染的流行率。
