Typhus is a contagiousbacterial disease which passes from person to person using lice as a vector. The bacteria cannot survive outside of a living cell for extended periods of time and other forms of person to person transmission are rare. Once a common and deadly disease, it is now very rare, affecting less than one person in a million in the modern world. It's decline is primarily due to the use of vaccination even though improved living conditions have played a role and antibiotics are effective against the disease.
Typhus used to thrive in crowded conditions, such as such as prisons, ships, army camps and even quarantine camps. Epidemics would often kill thousands of people, most notably in the great typhus epidemic of 1847 in Canada which killed 20,000 people. However, even though there were vaccines in use after World War I (although they were often dangerous), and the role of lice in the transmission of the disease was understood by the 1920s, it was only after World War II when more effective and safer vaccines became available that the disease started its decline.