Back in my school days, a girl in my class asked the teacher how a dog gets rabies. The teacher replied by being bitten by another dog with rabies. The girl then asked how that other dog got rabies, and the teacher admitted to not knowing.
Rabies is spread by contagion. So is malaria. I cannot contract malaria from a mosquito bite unless the mosquito has previously bitten an infected person (or perhaps animal).
How did the first dog to have rabies get rabies? How did the first person (or animal) with malaria get malaria.
Are there any answers?