Typhus fever is known as a historical scourge in times of war, famine and population upheaval, but this is only one of four types; the other three, each carried by a different insect, are still important causes of human disease in many parts of the world. The history of each type is described, and the intriguing recent discovery that the responsible bacteria are close cousins of the mitochondria which provide energy inside every living cell on the planet is discussed. About the Author George Cowan is a retired British Army physician with interests in tropical medicine who has worked on four continents and often cared for local people. His inquiry into typhus fever was stimulated by military cases of 'scrub typhus' in Malaysia and Singapore in 1970 and has since embraced the history of all four varieties of typhus. In 2008 he received an honorary doctorate from his alma mater, the University of St Andrews, after graduating with an honours degree in Humanities from the Open University in 2007.