M. canis is most often spread from contact with an infected animal or a contaminated environment, and therefore is by far the most likely to be a serious problem in a shelter. T. mentagrophytes is thought to be contracted mainly from exposure to rodent nests, and M. gypseum from contaminated soil, though the potential exists for spread from animal to animal in a contaminated environment.
Ringworm is very durable in the environment. Ringworm can persist on any surface and can infect animals housed in a contaminated environment months and even years later. For more information, refer to Environmental Decontamination.
Ringworm can be spread readily on grooming implements, contaminated toys and bedding, or by humans on clothing and hands. In nature, the incubation period for ringworm is between 4 days and 4 weeks. Ringworm can be found on the hair of animals from a contaminated environment even when the animal itself is not showing any signs.