Viruses like the covid virus are very small and rely on transmission via mucus membranes. Eyes nose mouth, they replicate in those areas, lungs, throat, mouth and then are transmitted in the saliva. Rarely does the viral load in the blood even come close to being enough to infect someone with some types of viruses.
The best example is HIV load in saliva or during any exposure, there are threshold limits and probability distribution for viral loads received by the person in contact that can help predict if you will get the virus or not.
Mosquito born illnesses like malaria being a living thing and Dengue and Zika being a virus can survive in the mosquitos as they are the vectors for transmission.
Washing your hands not sanitizer just washing your hands decreases your risk by 50 percent in some cases.