Spotted Fever Rickettsioses in Sweden : Aspects of Epidemiology, Clinical Manifestations and Co-infections

Sammanfattning: The spotted fever group rickettsiae are emerging diseases. They cause damage in their hosts by invading the endothelium in small to medium-sized blood vessels, which results in vasculitis that can cause clinical manifestations from most organs.The present thesis describes the prevalence of Rickettsia helvetica in ticks, the incidence of rickettsial infection based on seroreactivity and seroconversion in humans and their symptoms, from different parts of Sweden and the Åland Islands in Finland. This was accomplished through serological analysis of both retrospective and prospective serum samples from confirmed and suspected tick-bitten individuals compared to individuals with no knowledge of tick exposure (blood donors). We found a comparable seroprevalence to Rickettsia spp. in different geographical areas where ticks are present; it was also comparable to the seroprevalence of Borrelia spp. Seroprevalence was also more common, as suspected, in the tick-exposed group compared to blood donors. In comparison with co-infections with other tick-borne infections (Anaplasma spp. and Borrelia spp.), we could conclude that co-infections do exist and that, based on clinical findings, it is difficult to distinguish which microorganism causes certain clinical manifestations. For reliable conclusions regarding the causative microorganism, the diagnosis should basically rely on diagnostic tests. In comparison with Borrelia spp., seroconversion to Rickettisa spp. was more common in the areas we investigated, indicating that rickettsiosis is a common tick-borne infection in Sweden and most likely underdiagnosed.When investigating patients with meningitis, we found R. felis in cerebrospinal fluid from two patients with subacute meningitis. This was the first report in which R. felis was found and diagnosed in patients in Sweden. The patients recovered without sequelae and without causal treatment. To provide guidelines on when to treat Rickettisa spp. infections, more investigations are needed.The present thesis shows that Rickettsia spp. are common in ticks and do infect humans. Rickettsial infection should be considered in both non-specific or specific symptoms after a tick bite. It was also shown in the thesis that flea-borne rickettsiosis (R. felis) occurs in Sweden and may cause invasive infections