Occurrence of Rickettsia spp. in The Netherlands. Left: Map of the Netherlands showing the five locations that were sampled for this study. Right: Genetic variation of Rickettsia species found in The Netherlands. The phylogenetic relationship was based on a part of the 16SrRNA sequence: base 41 until 383 of R. prowazekii. The evolutionary distance values were determined by the method of Jukes and Cantor, and the tree was constructed according to the neighbor joining method. Cophenetic correlation coefficients, which are lower than 89%, are indicated at the nodes. 16SrRNA sequences from R. SP. IRS (L36102), IRS2 (DQ100164), IRS3 (AF141907) IRS4 (AF141908), rickettsii (L36217), helvetica (L36212), conorii (L36105), sibirica (L36218), canadensis (L36104), prowazekii (U29135), typhi (M20499), massiliae (L36106), bellii (L36103), felis (DQ102712), akari (L36099), and australis (L36101) were from Genbank. Between brackets the regions where the Rickettsia species were identified (AL = Ameland; BW = Bijlmerweide; DK = Duin en Kruidberg; HO= Heumesoord; HV= Houtvesterijen). No names are given to Rickettsia (sub)species which are not identical to the sequences in Genbank(e.g. AL-ticks).