Abstract
Mosquitoes of the Aedes genus transmit arboviruses of great importance to human health as dengue, chikungunya, Zika and yellow fever. The tiger mosquito Aedes albopictus can play an important role as arboviral vector, especially when Aedes aegypti is absent or present at low levels. Remarkably, the rapid worldwide spreading of the tiger mosquito is expanding the risk of arboviral transmission also to temperate areas, and the autochthonous cases of chikungunya, dengue and Zika in Europe emphasize the need for improved monitoring and control. Proteomic and transcriptomic studies on blood feeding arthropod salivary proteins paved the way toward the exploitation of genus-specific mosquito salivary proteins for the development of novel tools to evaluate human exposure to mosquito bites. We previously found that the culicine-specific 34k2 salivary protein from Ae. albopictus (al34k2) evokes specific IgG responses in experimentally exposed mice, and provided preliminary evidence of its immunogenicity to humans. In this study we measured IgG responses to al34k2 and to Ae. albopictus salivary gland protein extracts (SGE) in individuals naturally exposed to the tiger mosquito. Sera were collected in two areas of Northeast Italy (Padova and Belluno) during two different time periods: at the end of the low- and shortly after the high-density mosquito seasons. Anti-SGE and anti-al34k2 IgG levels increased after the summer period of exposure to mosquito bites and were higher in Padova as compared to Belluno. An age-dependent decrease of anti-saliva IgG responses was found especially in Padova, an area with at least 25 years history of Ae. albopictus colonization. Moreover, a weak correlation between anti-saliva IgG levels and individual perception of mosquito bites by study participants was found. Finally, determination of anti-al34k2 IgG1 and IgG4 levels indicated a large predominance of IgG1 antibodies. Overall, this study provides a convincing indication that antibody responses to al34k2 may be regarded as a reliable candidate marker to detect temporal and/or spatial variation of human exposure to Ae. albopictus; a serological tool of this kind may prove useful both for epidemiological studies and to estimate the effectiveness of anti-vectorial measures.
Highlights
Arboviruses as dengue, chikungunya, Zika and yellow fever have been responsible for severe outbreaks in the last decades, causing tens of thousands deaths per year with heavy public health impact and important global economic losses (WilderSmith et al, 2017)
A highly significant increase of both anti-al34k2 IgG1 and IgG4 levels was observed in PD2 by pairwise comparisons between paired samples (n = 68, p < 0.0001; Figure 4B); instead, only IgG4 levels showed a weakly significant increase after summer when all samples were considered (p = 0.0326, Figure 4A). These results clearly indicate that antibody responses against the al34k2 salivary protein show a large predominance of IgG1 antibodies
To make sure that age distribution did not represent a source of bias we compared the age of the different cohorts of individuals (PD1, PD2, PD paired, BL1, BL2, BL paired) by the Kruskal-Wallis or Mann-Whitney tests and found no significant difference
Summary
Arboviruses as dengue, chikungunya, Zika and yellow fever have been responsible for severe outbreaks in the last decades, causing tens of thousands deaths per year with heavy public health impact and important global economic losses (WilderSmith et al, 2017). A dengue vaccine has been approved by FDA in 2019 but its use appears to have some limitations (CDC, 2019; Espana et al, 2019), and despite the availability of a safe and effective vaccine for yellow fever, the disease is still endemic in Africa and in Central-South America (WHO, 2019). In this scenario, vector monitoring and control, along with the prevention of humanmosquito contact, still represent the main methods to contain the transmission of these arboviral diseases
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