The rapid world-wide spread of Aedes albopictus, a vector of relevant arboviral diseases like chikungunya and dengue, points up the need for better control strategies. Because of the important limits of methods currently used to assess human exposure to Aedes mosquito bites, much effort is being devoted to develop new indicators. Recently, we showed that the Ae. albopictus salivary protein al34k2, evokes specific IgG responses in mice exposed to the tiger mosquito and provided preliminary evidence of its immunogenicity to humans [1]. Also, we observe that in humans naturally exposed to the tiger mosquito bites in Italy the anti-al34k2 IgG responses appear suitable to evaluate seasonal variations of human exposure to Ae. albopictus [2]. The objective of this study is to evaluate the specific IgG response to al34k2 in individuals from different epidemiological settings where arboviruses are endemic and the main vector is Ae. albopictus. ELISA will be performed to evaluate specific IgG responses to al34k2 in adults exposed to Ae. albopictus in La Reunion Island. To check the potential cross-reactivity of al34k2 the specific IgG response will be tested in human samples exposed to Ae. aegypti in Bolivia. This would be a step forward in the establishment of a serological toolbox for the simultaneous assessment of human exposure to Aedes vectors and the pathogens they transmit.
References:
1. Buezo Montero, S.; Gabrieli, P.; Severini, F.; et al. Analysis in a murine model points to IgG responses against the 34k2 salivary proteins from Aedes albopictus and Aedes aegypti as novel promising candidate markers of host exposure to Aedes mosquitoes.2019 PLoS Negl Trop Dis 13:e0007806.
2. Buezo Montero, S.; Gabrieli, P.; Montarsi, F.; et al. IgG antibody responses to the Aedes albopictus 34k2 salivary protein as novel candidate marker of human exposure to the tiger mosquito. 2020 Front. Cell. Infect. Microbiol. (manuscript under revision, ID: 541768)
The innovativeness of this project consists in a development of an immunological assay to evaluate human exposure to Aedes mosquitoes, and more specifically to Aedes albopictus, by measuring the IgG response to al34k2 salivary protein by ELISA. The development of such tool may represent an advance for several reasons as epidemiological evaluation of Aedes-borne diseases is currently based on pathogen detection in human populations and entomological indirect methods with numerous limitations. Certainly, using these classical entomological methods for estimation of immature stage densities is time consuming and expensive with problems of inaccessibility to all potential breeding sites. Moreover, larval and pupal indicators are focused on immature stages that do not fully correlate to the density of adult mosquitoes. The estimation of adult female densities using human landing catches could be more significant for sampling host-seeking mosquitoes and then determining human exposure levels. However, due to the infection risk of exposed volunteers to mosquito vector bites, this method recalls obvious ethical issues that limit its application. Immuno-epidemiological assays are new, simple, rapid and sensitive and they would give a direct measure of human-vector contact. Besides, it would be a valuable tool for monitoring exposure not only at population but also at individual level. Finally, this approach may be also used for the evaluation of control interventions and of the risk of dissemination of diseases transmitted by Aedes mosquitoes.
The study described here represents a further step on the validation of human exposure to Ae. albopictus by quantifying the IgG response to al34k2 salivary protein. In Reunion Island, an area of chikungunya transmission, it was shown that the level of Ab against Ae. albopictus SGE can be used to identify individuals who have been exposed to the bites of this important vector. Low level cross-reactivity was observed with Ae. aegypti SGE suggesting that it will be possible to develop a specific biomarker for human exposure to Ae. albopictus bites [1]. Our previous results suggested that al34k2 may be a novel reliable candidate as marker to evaluate spatial and/or temporal variation of human naturally exposed to Ae. albopictus in Northeast Italy. It still to know if anti-al34k2 IgG levels represent a specie-specific marker or could expose a cross-reactivity with other Aedes mosquitoes. This project would validate the suitability of al34k2 as a biomarker of human exposure to Ae. albopictus in different epidemiological settings where arboviruses are endemic, and the main vector is the tiger mosquito. By combining the use of such a biomarker with classical entomological and epidemiological methods, it could enhance the assessment of human exposure to Ae. albopictus and therefore contribute to both accurate prediction of the risk of arbovirus transmission and evaluation of the efficacy of vector control.
References:
1. Doucoure S, Mouchet F, Cornelie S, et al. (2012) Evaluation of the Human IgG Antibody Response to Aedes albopictus Saliva as a New Specific Biomarker of Exposure to Vector Bites. PLoS Negl Trop Dis 6(2): e1487.