Polar bears appear to be less affected by infectious diseases and parasites than most terrestrial mammals. Polar bears are especially susceptible to "Trichinella", a parasitic roundworm they contract through cannibalism, although infections are usually not fatal. Only one case of a polar bear with rabies has been documented, even though polar bears frequently interact with Arctic foxes, which often carry rabies. Bacterial leptospirosis and "Morbillivirus" have been recorded. Polar bears sometimes have problems with various skin diseases that may be caused by mites or other parasites.