The main transmission mode of the viruses is through mosquito bites – the Culex pipiens mosquito mainly responsible for transmitting WNV, the Aedes aegypti and Aedes albopictus for CHIKV. CHIKV is transmitted to humans by the bite of infected mosquitoes. Humans are the only known hosts for CHIKV. For WNV, humans and birds are both hosts, of which only birds are amplifying hosts. This means that in birds the virus is able to amplify to produce sufficient viral levels to be transmitted to other biting mosquitoes which then infect other birds and also humans and horses.
Migratory routes inside the vector
The mosquito ingests the virus during a blood-meal (from humans in case of CHIKV and from birds in case of WNV)(1). The virus then passes through the midgut (2-4) towards the salivary glands (5), from where it can be transmitted to a suitable vertebrate host during another blood-meal.