Mode of transmission of relapsing fever

The bacteria that cause RF infect body lice when they take a blood meal from an infected person (figure below). The bacteria multiply in the gut of the louse, but the infection is not transmitted to new hosts when the louse bites a healthy person. Instead, humans acquire the infection when they scratch their bites and accidentally crush a louse, releasing its infected body fluids onto their skin. The bacteria enter through breaks in the skin, typically caused by scratching the itchy louse bites. After entering into the skin, the bacteria multiply in the person's blood and they can also be found in the liver, lymph glands, spleen and brain.