Infecting mosquitoes alters DENV-2 characteristics and enhances hemorrhage-induction potential in Stat1-/- mice

Dengue is one of the most prevalent arthropod-borne viral diseases in humans. There is still no effective vaccine or treatment to date. Previous studies showed that mosquito-derived factors present in saliva or salivary gland extract (SGE) contribute to the pathogenesis of dengue. In this study, we aimed to investigate the interplay between mosquito vector and DENV and to address the question of whether the mosquito vector alters the virus that leads to consequential disease manifestations in the mammalian host. DENV2 cultured in C6/36 cell line (culture-DENV2) was injected to Aedes aegypti intrathoracically. Saliva was collected from infected mosquitoes 7 days later. Exploiting the sensitivity of Stat1-/- mice to low dose of DENV2 delivered intradermally, we showed that DENV2 collected in infected mosquito saliva (msq-DENV2) induced more severe hemorrhage in mice than their culture counterpart. Msq-DENV2 was characterized by smaller particle size, larger plaque size and more rapid growth in mosquito as well as mammalian cell lines compared to culture-DENV2. In addition, msq-DENV2 was more efficient than culture-DENV2 in inducing Tnf mRNA production by mouse macrophage. Together, our results point to the possibility that the mosquito vector provides an environment that alters DENV2 by changing its growth characteristics as well as its potential to cause disease.
Author summary The transmission cycle of dengue virus involves a complex interaction of the virus with the mosquito vector and the human host. DENV enters the mosquito through an infectious blood meal. The virus first infects and replicates in the mosquito midgut before it is translocated to the hemolymph and ultimately reaches the salivary gland. The virus is then released to the saliva and transmitted to the human host through a mosquito blood meal. Previous studies showed that mosquito saliva, salivary gland proteins or mosquito bite modulates arbovirus infection in the mammalian host. Here, we investigate the interplay between the mosquito vector and DENV and address whether the virus is altered in the mosquito vector that consequentially influences disease manifestations in the mammalian host. By excluding the effect of saliva, we demonstrated that after infecting Aedes aegypti, DENV2 acquired the potential to induce more severe hemorrhage in Stat1-/- mice. Msq-DENV2 exhibited smaller particle size, larger plaque size and more rapid growth rate, and was also more efficient in inducing macrophage Tnf production compared to culture-DENV2. Taken together, our data support the notion that mosquito A. aegypti alters DENV2 by changing its growth characteristics as well as its potential to cause disease.