serve as possible explanations as to why bats carry so many viruses. One proposed theory is that there exist so many bat-borne illnesses because there exist a large amount of bat species and individuals. The second possibility is that something about bats' physiology make them especially good reservoir hosts. Perhaps bats' "food choices, population structure, ability to fly, seasonal migration and daily movement patterns, torpor and hibernation, life span, and roosting behaviors" are responsible for making them especially suitable reservoir hosts. Lyssaviruses (including the Rabies virus), Henipaviruses, Menangle and Tioman viruses, SARS-CoV-Like Viruses, and Ebola viruses have all been traced back to different species of bats. Fruit bats in particular serve as the reservoir host for Nipah virus (NiV). Rats Rats are known to be the reservoir hosts for a number of zoonotic diseases. Norway rats were found to be infested with the Lyme disease spirochetes. In Mexico rats are known carriers of Trypanosoma cruzi, which causes Chagas disease. Mice White-footed mice (Peromyscus leucopus) are one of the most important animal reservoirs for the Lyme disease spirochete (Borrelia burgdorferi). Deer mice serve as reservoir hosts for Sin Nombre virus, which causes hantavirus pulmonary syndrome (HPS). Monkeys The Zika virus originated from monkeys in Africa. In São José do Rio Preto and Belo Horizonte, Brazil the zika virus has been found in dead monkeys. Genome sequencing has revealed the virus to be very similar to the type that infects humans. Environmental reservoirs Environmental reservoirs include living and non-living reservoirs that harbor infectious pathogens outside the bodies of animals. These reservoirs may exist on land (plants and soil), in water, or in the air. Pathogens found in these reservoirs are sometimes free-living. The bacteria Legionella pneumophila, a facultative intracellular parasite which causes Legionnaires' disease, and Vibrio cholerae, which causes cholera, can both exist as free-living parasites in certain water sources as well as in invertebrate animal hosts. Disease transmission A disease reservoir acts as a transmission point between a pathogen and a susceptible host. Transmission can occur directly or indirectly. Direct transmission Direct transmission can occur from direct contact or direct droplet spread. Direct contact transmission between two people can happen through skin contact, kissing, and sexual contact. Humans serving as disease reservoirs can be symptomatic (showing illness) or asymptomatic (not showing illness), act as disease carriers, and often spread illness unknowingly. Human carriers commonly transmit disease because they do not realize