Starvation at the larval stage increases the vector competence of Aedes aegypti females for Zika virus

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.
Author summary When mosquitoes are reared in a laboratory they are typically provided with ample nutrients as larvae so adults can grow to an optimal size; this ensures adults are robust for reproducible experiments. However, in the field not all larvae may have access to equal amounts of food. Studies including ours have shown that by restricting food as larvae, smaller adults can be produced, which can have an altered ability to be infected with and transmit arthropod-borne viruses. Zika virus is ingested into a female mosquito midgut when a blood-meal is acquired from an infected vertebrate host; the virus must infect midgut cells and escape this tissue to secondary tissues via the basal lamina, which surrounds the midgut. Viruses can then infect other organs including the salivary glands, for further transmission. In this study we focus on the impact limited nutrition as a larva has on the adult’s transmission potential for Zika virus.