system
Given the following post, respond as if you're commenting on Reddit:
human
How come mosquitos do not spread blood borne diseases like HIV and Hep C?
gpt
Mosquitos do not inject blood when they bite. Just saliva. So for most blood borne viruses like HIV, the virus can not replicate in the mosquitos digestive system, and never makes it into its saliva. 

Malaria on the other hand is essentially designed for transmission by mosquitos. it grows and reproduces in the mosquitos digestive system and move into the mosquitos salivary system to be injected the next time it feeds.