Which vector is primarily responsible for transmitting Rocky Mountain spotted fever?

Rocky Mountain spotted fever is primarily transmitted by ticks, specifically the Rocky Mountain wood tick and the American dog tick. These ticks become infected with the Rickettsia rickettsii bacterium, which causes the disease, when they feed on infected animals such as rodents or other hosts. The transmission occurs during the tick's feeding process, as the bacteria enter the bloodstream of the host through the tick's saliva.

In the context of the other choices, mosquitoes are known for transmitting diseases like malaria and dengue fever, but they do not play a role in the transmission of Rocky Mountain spotted fever. Similarly, fleas are vectors for diseases such as plague and typhus, but are not involved in the transmission of this specific disease. Worms, although they have their own range of medical implications, do not serve as vectors for this bacterial infection. Therefore, the correct choice reflects the specific understanding of the disease's vector in relation to its biological transmission dynamics.