Coloured TEM of Rickettsiae bacterium. © Science Photo Library

Rickettsiosis/rickettsioses are a group of diseases generally caused by species of Rickettsia, a genus of obligate intracellular bacteria. Most of the Rickettsioses are transmitted by ticks, but they can also be transmitted by fleas, lice and mites. Although they are widely distributed throughout the world, the species and associated human clinical diseases vary depending on the geographical locations. Rickettsiosis can be classified into two main groups: the spotted fever group, transmitted by ticks or mites and the typhus group, mainly transmitted by lice or fleas. Many new pathogenic Rickettsiae continue to be identified in recent years.