Found mostly in warm tropical areas around the world, Malaria itself isn’t a virus but rather a kind of parasite that can be spread via the saliva of mosquitoes.
In some cases smelly drains are caused by the loss of the seal created by the plumbing trap. Basically this is where the water level in the trap drops below the u-bend in the pipe, allowing for the free passage of gasses back and forth.
If your drain is blocked it is best not to put off getting it fixed, and not just because it smells bad. The problem can get worse and worse and as time goes by, it can become ever more expensive to fix.