6.1.3 Relative humidity
Relative humidity refers to the amount of moisture in the air, expressed as a percentage; (0% humidity would mean the air is completely free of moisture and 100% humidity would mean the air is completely saturated with moisture). Relative humidity affects malaria transmission through its effect on the activity and survival of mosquitoes. You may recall that mosquitoes need to live at least 8–10 days to be able to transmit malaria.
Why is it important that mosquitoes should live this long, for the transmission of malaria?
This is the length of time required for the parasite to develop inside the mosquito host. If the mosquito dies before the parasite has developed, then transmission of the parasite cannot occur.
Mosquitoes survive better under conditions of high humidity. They also become more active when humidity rises. This is why they are more active and prefer feeding during the night – the relative humidity of the environment is higher at night. If the average monthly relative humidity is below 60%, it is believed that the life of the mosquito is so short that very little or no malaria transmission is possible.
6.1.2 Rainfall