What is the role of the mosquito as a vector?

A person or an animal has a blood borne disease such as malaria or yellow fever. For that disease to get to another person, it has to move to the other person's blood stream. How will it do it?

A cold infects your nose. When you sneeze, someone else breathes that air and catches your cold.

Flu infects your throat. When you cough, someone else breaches that air and catches your flu.

People do not normally breathe your blood.

There is a little animal called a female mosquito that eats your blood. Then it eats someone else's blood. Now if you have a blood borne disease it will go into the mosquito when it eats your blood.

Malaria then becomes part of the mosquitoes saliva. Its saliva acts like drilling fluid. The mosquito uses it to drill through your skin. (Oil field workers use drilling fluid to drill oil wells.) The disease gets into the new person.

The vector was the item, in this case the animal or mosquito that carried the disease from one person to the other.