Implications of vertical transmission of Alphaviruses in Aedes aegypti mosquitoes

Mosquitoes are vectors for epidemic transmission of viruses of public and veterinary health. The mosquito vector is generally infected for life although, unlike the vertebrate counterpart, does not suffer a high fitness cost. Having a vector infected for the length of its life enables routes of viral transmission other than the classic infected bite (horizontal), including sexual (horizontal) and to the progeny (vertical). Vertical transmission is considered a route of transmission that allows for the persistence of the virus during adverse environmental periods (e.g., droughts, cold periods). Because Aedes aegypti and Aedes albopictus eggs are resistant to dessication, it is hypothesised that this attribute could promote arbovirus survival between transmission cycles, playing an important role in maintaining the pathogen.

Vertical transmission of arboviruses has been extensively documented for flaviviruses and bunyaviruses. However, there is very little and contradictory reports of vertical transmission of alphaviruses. In this research we establish the mechanisms of vertical transmission of the alphaviruses Semiliki Forest virus (SFV) and Ross river virus (RRV) and its implications in pathogen transmission of future generations.

Aedes aegypti mosquitoes were infected with SFV virus in different gonotrophic cycles. Their offspring was then reared and challenged with SFV, RRV and dengue virus (DENV). Offspring from infected parents showed significant reduction in viral load if infected with SFV or RRV but not with DENV.

Findings of this research highlight the importance of vertical transmission of alphaviruses in the general arbovirus infectious cycle.