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during february 1999 , a 39-year - old woman sought treatment at a hospital in kijabe , kenya , for a  boil  on her lower left leg . over the next 3 days , headache , myalgia , chills , sweats , and a fever of 38.5c developed .
the patient was a missionary from the united states , who frequently hiked in the forest around kijabe with her dog .
four days before discovering the lesion on her leg , she had taken her ill dog to the local veterinarian .
( an unspecified illness in dogs , associated with tick infestation ) and was treated with imizol ( imidocarb dipropionate ) .
five days after the onset of her symptoms , the patient returned to the hospital when her condition had not improved .
hematologic evaluation showed a marginal decrease in leucocytes to 4,200/mm ( 80% polymorphonuclear cells , 2% bands , 17% lymphocytes , and 1% eosinophils ) , and thrombocytopenia ( 107,000/mm ) .
the next day , the patient returned to the hospital after the onset of vomiting and a nonpuritic , blotchy , macular rash on her arms and abdomen . because she had traveled recently to a malaria - endemic area ,
treatment was initiated with three tablets of fansidar ( 500 mg sulfadoxine and 25 mg pyrimethamine per tablet ) .
the patient reported some improvement of symptoms that evening , and by the following day , she ceased vomiting and her fever was reduced . on the day 9 of her illness , a generalized macular rash covered her full body , sparing her palms and soles .
that evening she became mildly confused and was admitted to kijabe african inland church mission hospital .
an eschar surrounded by a 1.5 cm purpuric border was identified on her lower left leg .
fansidar - resistant malaria as well as a viral exanthem were diagnosed , and she was treated with intravenous fluids , quinine , acetaminophen , and promethazine . the following day ,
multiple seizures developed , and she went into cardiopulmonary arrest . despite attempts at cardiopulmonary resuscitation , the patient died .
histopathologic findings included extensive epidermal and dermal necrosis and acute inflammation at the site of the eschar with focal , transmural , mixed inflammatory cell infiltrates involving dermal blood vessels ( figure 1 ) .
vasculitis and edema involving medium - sized artery in the subcutaneous fat at the site of the eschar ( hematoxylin and eosin stain ; original magnification x100 ) .
formalin - fixed , paraffin - embedded tissue and serum specimens were sent to the centers for disease control and prevention for evaluation .
immunohistochemical ( ihc ) staining for sfg rickettsia demonstrated rickettsiae and rickettsial antigens in sections of heart , spleen , and kidney localized within and around vascular endothelial cells and reticuloendothelial cells , predominantly in areas associated with perivascular mononuclear inflammatory infiltrates ( figure 2 ) .
immunohistochemical localization of spotted fever group rickettsial antigens in various tissues of a patient with fatal spotted fever rickettsiosis , by immunoalkaline phosphatase stain with naphthol phosphate 
rickettsiae and rickettsial antigens ( red ) in kupffer cells in liver ( a ) , perivascular infiltrates in skin ( b ) , and glomerular endothelium in kidney ( c ) ( naphthol  fast red stain with hematoxylin counterstain ; original magnifications x158 ) . a single serum sample , collected on the ninth day of illness , demonstrated neither immunoglobulin ( ig ) g nor igm antibodies reactive with r. conorii when tested by an indirect immunofluorescence antibody assay at a screening dilution of 1:16 .
to further define the causative agent , we attempted to amplify a portion of the rickettsial rompa gene , as we have done for ticks from this region ( 4 ) , using dna extracted from the paraffin - embedded sections of heart , spleen , and kidneys .
briefly , paraffin - embedded tissue samples were deparaffinized in xylene , and rinsed in absolute ethanol .
genomic dna was extracted by using the wizard genomic dna purification kit ( promega , madison , wi ) , according to the manufacturer s protocol . amplification of a 635-bp fragment of the rompa gene encoding the sfg - specific 190-kda protein was attempted by using primers rr190.70p ( 7 ) and rr190.701 ( 8) . genomic dna isolated from r. montanensis  infected vero cells , and water served as positive and negative controls , respectively , for the polymerase chain reaction ( pcr ) .
immunostaining demonstrated an sfg rickettsial infection as the cause of the patient s death ; yet , because the ihc assay reacts with several species of sfg rickettsiae ( 9 ) , a specific etiologic agent was not determined .
serologic evaluation of a serum specimen obtained late in the course of this patient s illness failed to demonstrate antibody reactive with sfg rickettsiae ; however , some patients with fatal rickettsial infections die before notable levels of these antibodies are detected ( 9 ) . additionally , repeated attempts to amplify rickettsial dna from numerous thin - section preparations from paraffin - embedded tissues were unsuccessful . therefore , we were unable to characterize the infecting rickettsiae using molecular techniques .
sample fixation procedures may decrease the sensitivity of the pcr , as seen in diagnostic assays for other microorganisms ( 10 ) .
further work is needed to determine the utility of pcr as a reliable method of detecting rickettsial dna in paraffin - embedded tissues .
r. conorii causes a moderate to severe illness with a case - fatality rate of approximately 3% .
disease is most often characterized by a single eschar and a generalized maculopapular rash that may involve the palms and the soles ( 11 ) . by contrast
, r. africae causes a generally milder , self - limiting disease with fever , multiple eschars , regional lymphadenopathy , and rash in approximately 16% to 46% of patients ( 3,12 ) .
anecdotal reports and some animal and human studies suggest that sulfa - containing antimicrobial agents exacerbate the clinical severity of rickettsial infections ( 13,14 ) , and the patient described here received a sulfa - containing antibiotic after malaria was diagnosed .
however , an early correct diagnosis and prompt administration of effective antirickettsial therapy ( e.g. , doxycycline or another tertacycline ) remain the primary determinants of successful clinical outcomes for patients with spotted fever rickettsioses .
evidence is accumulating that tick - borne rickettsiosis are an underreported and underappreciated cause of illness in sub - saharan africa .
for example , while investigating this case we discovered that a mild febrile illness , accompanied by rash , developed in nearly one third of a group of boarding school students from the united states , who had camped at masai mara , a popular tourist destination ; all had histories of tick bite ( j. rutherford , unpub .
additionally , recent identification of sfg rickettsiae in ticks from this area confirmed the presence of r. africae in amblyomma variegatum collected from domesticated livestock ( 4 ) .
rickettsial infections in central and sub - saharan africa have been reported among tourists and travelers who visited game reserves ( 12 ) .
the prevalence of spotted fever in local populations may be obscured by the lack of obvious rash and the overwhelming number of cases of malaria .
this case report highlights both an immediate and a long - term need for rickettsial surveillance and dissemination of information about rickettsioses to health care workers in africa . in a similar manner ,
physicians in industrialized countries who care for ill travelers who have visited africa should consider rickettsial infections among the differential diagnoses of febrile disease , particularly in clinical situations in which malaria has been reasonably excluded as a cause of the patient s illness . in these contexts , further studies of the epidemiology and ecology of african sfg rickettsiae and rickettsioses are warranted .
we report a fatal case of rickettsiosis in a woman from the united states living in kenya , who had a history of tick exposure . 
 immunohistochemical staining of skin , kidney , and liver demonstrated spotted fever group rickettsiae . 
 the clinical findings , severity , and fatal outcome are most consistent with rickettsia conorii infection .