Rickettsia - a genus of mainly pathogenic bacteria, once thought to be viruses
The interesting thing about rickettsia spp. is that although they are bacteria, they behave like viruses in that they need to be inside a living host cell to survive. Many types of rickettsia cause disease in mammals. Due to their virus-like behaviour they have to be transferred via living organisms, usually via insect vectors, such as fleas, lice and mites.
Most types of rickettsia produce diseases showing similar symptoms. The bacteria grow in the cells lining the blood and lymph system and the syptoms are often similar to 'flu', but may include a rash. Some rickettsial diseases, particularly typhus and Rocky Mountain spotted fever, may be fatal, however unlike virus infections these can be successfully treated with antibiotics.
Rickettsias are named after their discoverer Harold Taylor Ricketts, who incidently died of epidemic typhus - a disease caused by rickettsia