Abstract
Aedes aegypti is the primary vector of Zika virus (ZIKV), a flavivirus which typically presents itself as febrile-like symptoms in humans but can also cause neurological and pregnancy complications. The transmission cycle of mosquito-borne arboviruses such as ZIKV requires that various key tissues in the female mosquito get productively infected with the virus before the mosquito can transmit the virus to another vertebrate host. Following ingestion of a viremic blood-meal from a vertebrate, ZIKV initially infects the midgut epithelium before exiting the midgut after blood-meal digestion to disseminate to secondary tissues including the salivary glands. Here we investigated whether smaller Ae. aegypti females resulting from food deprivation as larvae exhibited an altered vector competence for blood-meal acquired ZIKV relative to larger mosquitoes. Midguts from small ‘Starve’ and large ‘Control’ Ae. aegypti were dissected to visualize by transmission electron microscopy (TEM) the midgut basal lamina (BL) as physical evidence for the midgut escape barrier showing Starve mosquitoes with a significantly thinner midgut BL than Control mosquitoes at two timepoints. ZIKV replication was inhibited in Starve mosquitoes following intrathoracic injection of virus, however, Starve mosquitoes exhibited a significantly higher midgut escape and population dissemination rate at 9 days post-infection (dpi) via blood-meal, with more virus present in saliva and head tissue than Control by 10 dpi and 14 dpi, respectively. These results indicate that Ae. aegypti developing under stressful conditions potentially exhibit higher midgut infection and dissemination rates for ZIKV as adults, Thus, variation in food intake as larvae is potentially a source for variable vector competence levels of the emerged adults for the virus.
Highlights
Aedes aegypti mosquitoes are the primary vectors of Zika virus (ZIKV; Flaviviridae, Flavivirus) [1], which typically causes febrile illness when transmitted to humans, but can cause serious health conditions such as neurological Guillian Barresyndrome, and pregnancy complications including stillbirth and microcephaly in unborn children [2,3,4][reviewed in [5]
We show that smaller Small nutritionally deprived (Starve) Ae. aegypti have an increased transmission potential for ZIKV and a thinner midgut basal lamina (BL) relative to Control mosquitoes
Examples of BL measurements taken from Control and Starve midguts at 5 dpi are shown in Fig 1A and 1B, respectively
Summary
Aedes aegypti mosquitoes are the primary vectors of Zika virus (ZIKV; Flaviviridae, Flavivirus) [1], which typically causes febrile illness when transmitted to humans, but can cause serious health conditions such as neurological Guillian Barresyndrome, and pregnancy complications including stillbirth and microcephaly in unborn children [2,3,4][reviewed in [5]. ZIKV cases have declined in recent years, the threat of renewed outbreaks in the future is continuing, justifying the need to study the factors influencing mosquito vector competence for the virus. Once Ae. aegypti eggs hatch, larvae require food to moult through four instars, transitioning into non-feeding pupae that will eclose into winged adults [8]. Once a larva moults into a fourth instar, if feeding is suspended, so is the development into a pupa. These fourth instar larvae have been shown to tolerate starvation conditions for up to two weeks, resuming pupation if fed again [10]
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