Which of the following is an example of a vector?

A vector in the context of infectious diseases is an organism that does not cause disease itself but spreads infection by conveying pathogens from one host to another. Ticks serve as a prime example of a vector because they can carry and transmit pathogens, such as those that cause Lyme disease and Rocky Mountain spotted fever, from infected animals to humans.

The other options listed, such as Staphylococcus bacteria and Salmonella, are examples of pathogens that can cause diseases directly. They do not act as carriers or transporters for other pathogens but are themselves infectious agents. Houseflies, while they can be associated with the spread of some diseases, do not function as vectors in the same specific sense as ticks do, which have a defined role in the transmission of certain pathogens. Therefore, ticks are recognized as a clear example of a vector due to their capability to transfer diseases through their bites.