"Pathogens are often transmitted from animals to humans accidentally, for example via infected meat or water contaminated with animal feces. But there are two transmission routes in which the animal is an essential agent in the transfer of pathogens to humans. An example of zoonosis that may be familiar is influenza originating in pigs, or swine flu, or poultry, or bird flu. The influenza viruses that cause these diseases can sometimes be transmitted from animals to humans during the slaughter or handling of livestock. Some zoonotic influenza viruses pose a much greater health risk than the airborne seasonal influenza viruses that commonly circulate in human populations every winter. Another route of transmission from animals to humans results in vector-borne infections. They differ from zoonoses in that they are transmitted by an invertebrate animal, mainly biting insects and ticks. The term vector comes from the Latin word for carrier, so in this context it means a carrier of an infectious disease. The pathogen must complete part of its life cycle in the vector, so transmission to humans may be prevented if the vectors can be killed. For example, Lyme disease is caused by a bacterium transmitted from birds or small mammals, such as deer, to humans by a type of tick. There are many other vector-borne infections, including bubonic plague transmitted by rat fleas, typhus transmitted by ticks, and yellow fever transmitted by mosquitoes. In 2014, the World Health Organization devoted its annual World Health Day to publicize the risk from vector-borne infections."