Chikungunya Virus Transmission
Chikungunya viruses are transmitted to humans through the bites of infective female Aedes mosquitoes. The mosquitoes generally acquire the virus while feeding on the blood of an infected person. After virus incubation for eight to ten days, an infected mosquito is capable, during probing and blood feeding, of transmitting the virus for the rest of its life. There is no way to tell if a mosquito is carrying the chikungunya virus. Infected female mosquitoes may also transmit the virus to their offspring by transovarial (via the eggs) transmission, but the role of this in sustaining transmission of the virus to humans has not yet been defined.
Infected humans are the main carriers and multipliers of the virus, and serving as a source of the virus for uninfected mosquitoes. The virus circulates in the blood of infected humans for several days, at approximately the same time that they have chikungunya fever (see also clinical symptoms). Aedes mosquitoes may acquire the virus when they feed on an individual during this period. In parts of Asia and Africa, the transmission cycle may also involve jungle primates that act as a reservoir for the virus (see figure 1).
Figure 1. Transmission of chikungunya viruses. Source: PLoS Negl Trop Dis. 2010 Apr 27;4(4):e623
The Aedes mosquito prefers to breed in water-filled receptacles, usually close to human habitation. They often rest in dark rooms (e.g. in bathrooms and under beds) and breed in small pools that collect in discarded human waste (see figure 2). Although they are most active during daylight hours, biting from dawn to dusk, mosquitoes will feed throughout the day indoors and during overcast weather.