A vector is an animal or insect that is necessary for the transmission of certain contagious diseases from person to person that otherwise could not be directly transmitted from person to person. The disease also cannot be capable of living outside of a living body. Some examples of diseases that require vectors are:
- Malaria, which is transmitted from person to person from the bite of the mosquito.
- Bubonic plague, which is transmitted from host to host through the bite of fleas.
- Lyme disease, which is transmitted from host to host through the bite of a tick.
- Rabies, which is transmitted by being bitten by an infected animal, such as a dog, rat, or bat.
- Tapeworm, which has a complicated life cycle where the eggs of the worm are excreted in feces and grow in another host, such as pigs or fish depending on the species, and are then eaten.