in march 2003 , a 23-year - old man ( patient 1 ) sought treatment for fever ( 39.3c ) , headache , and an eschar on his right thigh . no diagnosis was made , but he was given penicillin v. seven days later he returned with worsening symptoms of fever ( 39.9c ) , headache , cough , arthralgia , and lethargy . a provisional diagnosis of scrub typhus was made , and he was given doxycycline . by the next day he was afebrile , and his condition was much improved . the diagnosis was confirmed by a positive serologic result for scrub typhus rickettsiae ( antibody titer 512 ) and the presence of o. tsutsugamushi in blood detected on day 7 by pcr and culture ( table ) . * sfg , spotted fever group ; antigens were r. honei , r. australis , r. akari , r. conorii , r. siberica , and r. rickettsii . stg , scrub typus group ; antigens were the o. tsutsugamushi strains gilliam and kato . in may 2004 , an 11-year - old boy ( patient 2 ) was examined because of a 3-day history of fever ( 39.0c ) , headache , nausea , abdominal pain , and a boil surrounded by cellulitis behind his left ear . his blood was tested for malaria , dengue , and scrub typhus , but he was given no antimicrobial therapy . he was not seen again until day 18 , when he was prescribed doxycycline after pcr detected o. tsutsugamushi ( and it was later isolated ) in his day-10 blood sample . follow - up serologic testing of samples collected on days 10 and 33 displayed seroconversion to antibodies against scrub typhus ( titers < 128 to > 1,024 ; table ) . in april 2003 , a 29-year - old man ( patient 3 ) sought treatment for fever ( 38.4c ) , cough , nausea , lethargy , and cellulitis of both feet . three days later , he was evacuated by air and admitted to the thursday island hospital , at which time he was still febrile ( 39.2c ) but had no cellulitis . he also had a macular rash , which he reported as originally having been pustular ; the thigh lesions were recognized as eschars . a tentative diagnosis of scrub typhus was made , and the patient was given doxycycline . serologic testing for rickettsiae was positive for the spotted fever group ( titer 256 ) on day 3 , but the titers remained unchanged 4 months later . a spotted fever group rickettsial organism was grown from the day-3 blood sample ; however , pcr was negative for rickettsiae ( table ) . rickettsial serologic testing was performed on patients paired serum specimens by using an indirect immunofluorescence assay ( 6 ) . patient 1 had an increase in titer to o. tsutsugamushi ; patient 2 exhibited seroconversion to o. tsutsugamushi antibodies ; and patient 3 had stationary positive titers to spotted fever group rickettsiae ( table ) . a spotted fever group rickettsial organism was isolated from patient 3 , and an orientia organism was isolated from patients 1 and 2 ( table ) . we extracted dna from enriched buffy coat and rickettsial cultures by using the qiaamp blood mini kit ( qiagen , hilden , germany ) and following the manufacturer s protocols . scrub typhus was diagnosed by 56-kda gene pcr , which used the primers a ( 5-tacattagctgcaggtatgaca-3 ) and b ( 5-ccagcataattctttaaccaag-3 ) ( invitrogen , mount waverley , victoria , australia ) as previously described , without the nested procedure and with a 51c annealing temperature ( 8) . buffy coats and cultures from patients 1 and 2 were pcr positive for o. tsutsugamushi ( table ) . the 320-bp product ( patient 2 ) was sequenced ( newcastle dna , university of newcastle , australia ; genbank accession no . ay860955 ) and shared 89.8% homology with the taiwanese strains tw381 and tw521 ( genbank accession nos . ay222635 and ay222630 , respectively ) . a phylogenetic tree of the 56-kda antigen gene was constructed by using the seqboot and consense programs of the phylip software package ( figure ) . phylogenetic tree obtained by a neighbor - joining analysis of the 56-kda gene of orientia tsutsugamushi . bootstrap values from 100 analyses are shown at the node of each branch . spotted fever group rickettsemia was identified by 17-kda antigen gene pcr that used the primers mto-1 ( 5-gctcttgcaactctatgtt-3 ) and mto-2 ( 5-cattgttcgtcaggttggcg-3 ) ( invitrogen ) as previously described , with an annealing temperature of 51c and 45 cycles ( 9 ) . the 17-kda buffy coat pcr result was negative for patient 3 , but the culture gave a 413-bp sequence that was 100% homologous with r. australis ( genbank accession no . the patient s buffy coat dna extract was not tested for pcr inhibitors , and no attempt was made to use the r. australis isolate in a heterologous serologic reaction because the strain could not be established in continuous culture . isolation of r. australis from a patient on darnley island redefines the northern limit of distribution of queensland tick typhus in australia . previously , queensland tick typhus had been thought to extend from wilson s promontory ( the tip of southeastern australia ) ( 10 ) to the atherton tableland ( north queensland ) ( 2 ) . this more northern finding of queensland tick typhus was not unexpected because distribution of the vector of queensland tick typhus in northeastern australia , ixodes holocyclus , is likely to include the torres strait islands and papua new guinea ( 11 ) . rickettsial diseases that differ clinically from scrub typhus have been reported in papua new guinea ( 12 ) . a recent serologic survey found 7 ( 3.7% ) of 191 papua new guineans were seropositive to scrub typhus or spotted fever group rickettsiae ( 13 ) . another survey found that at least 19 ( 17% ) of 113 papua new guineans had an antibody titer > 256 against spotted fever group rickettsiae ( a.g . a spotted fever group rickettsial disease such as queensland tick typhus , flinders island spotted fever , or another undescribed rickettsiosis could explain these findings . low antibody titers ( 128 ) to the spotted fever group in the scrub typhus patients ( table ) are consistent with previous exposure to spotted fever group or typhus group rickettsiae . because 20% of each enriched buffy coat specimen was examined by rickettsial pcr and 80% by culture , results were skewed in favor of isolation rather than dna detection . since 1935 , numerous cases of scrub typhus have been reported in australia and papua new guinea ( 5,12 ) . scrub typhus is known to be endemic to darnley island ; however , strains have not been typed ( 5 ) . strains from northeastern australia were serologically determined to be karp or karp - related ( 14 ) . however , this new strain is 10.2% divergent from any other described strain , including karp ( figure ) . hence , we designated it as the darnley strain , after the island from which it was isolated . the phylogenetic relationship of the darnley strain to other australian strains , including litchfield , needs to be elucidated . the presence of 3 rickettsial diseases on this small island demonstrates the complexity of rickettsial epidemiology in australia .
we report 3 rickettsioses on darnley island , australia , in the torres strait . 
 in addition to previously described cases of flinders island spotted fever ( rickettsia honei strain  marmionii  ) , we describe 1 case of queensland tick typhus ( r. australis ) and 2 cases of scrub typhus caused by a unique strain ( orientia tsutsugamushi ) .