How can an organism carry parasites that would cause communicable diseases?

Question

Communicable diseases, parasites... (please answer my question, i need it for my homework, pls!)

Answer 1

Fleas are parasites, because they live on rats and do not benefit the rats.

Fleas carry many communicable diseases, most notably, bubonic plague, murine plague, murine typhus, and tularemia.

There are many other diseases spread by parasites. Rabies can be spread by bats that drink animal blood (vampire bats.) Mosquitoes probably cause more death from communicable diseases than any other animal.

Check the World Health Organization (WHO) infectious disease page and search for "insect vectors" for more, though insects are not the only parasites that spread disease.