Typhus is an acute disease caused by A bacterium named Rickettsia rickettsii is an infectious tick that carries the bacteria. These ticks live in wooded areas in low hedges and tall grass. The disease is more common in warm weather—spring and summer. Illness can occur at any age. But it is more common in adults aged 60 to 69 and children aged 5 to 9 years, and more in men than women.