Determining the global burden of rickettsial diseases can be problematic for a number of reasons. Often Rickettsial infections are miss-diagnosed as something else (the symptoms are very broad range and non-specific), or symptoms may be mild and go undocumented. Although rickettsial pathogens are found globally, there are many different species and these may be restricted to specific regions. With this distribution, and varying access to health facilities and rates of exposure, burden of infection will vary greatly from country to country and region to region. That said, for some of the most important rickettsial diseases we do have a good approximation of disease burden. In Southeast Asia, rickettsial infections are the second most frequently reported non-malarial disease, after dengue infections (that is of all the diseases other than malaria, rickettsia is the second most common infection). Scrub typhus (Orientia tsutsugamushi) has a seroprevalence ranging from 9.3% - 27.9% in Asia (that is 9.3 to 27.9% of the population has been exposed to scrub typhus in the past); whilst globally, it has been estimated that over a million scrub typhus cases occur each year and that a billion people are at risk of infection. In the USA, the most severe and most commonly reported rickettsial infection is Rocky Mountain spotted fever (RMSF) which is caused by Rickettsia rickettsii, with seven cases per million persons reported in 2007, and if left untreated may cause fatality rates as high as 20 - 25%.