In colder areas where people may live under unhygienic conditions and are infested with lice. Explosive epidemics may occur during war and famine. Endemic foci exist in the mountainous regions of Mexico, in Central and South America, in central and eastern Africa and numerous countries in Asia. Recent outbreaks have been observed in Burundi and Rwanda. This rickettsia exists as a zoonosis of flying squirrels (Glaucomys volans) in the USA, and there is serological evidence that humans have been infected from this source, possibly via the squirrel flea.