Detection oftheEtiologic AgentofHumanEhrlichiosis by Polymerase ChainReaction

Polymerase chain reaction (PCR)primers derived froma variable region ofthe16SrRNAgene sequence were usedtoamplify DNA specifically fromEhrlichia chaffeensis (the recently proposed name fortheetiologic agentofhumanehrlichiosis). The389-bp product defined bythespecific primers was notdetected whenDNA samples fromanyoftheother recognized species ofEhrlichia were usedasamplification templates. Whenthe PCRwas applied tofive suitable blood specimens obtained frompatients subsequently showntobeserologically positive forE.chaffeensis, allfive were positive. Thesame technique was applied toatotal ofsixcontrol blood specimens, three fromfebrile patients whohadno serologic evidence ofinfection withEhrlichia orRickettsia species andthree frompatients diagnosed withRockyMountain spotted fever, andallsixwere negative. A chemiluminescent, group-specific oligonucleotide probe was showntohybridize onlywiththePCR products obtained upon amplification ofthefive blood specimens frompatients serologically diagnosed ashaving human ehrlichiosis. Theresults indicate thatPCR,coupled with a nonisotopic methodofconfirming theidentity ofthe PCRproduct, isahighly specific andefficient methodofdetecting theagentofhumanehrlichiosis inblood. The results also suggest that E.chaffeensis isthesole etiologic agentofhumanehrlichiosis intheUnited States. The technique was alsoapplied tofourticks that were positive bydirect immunofluorescence forEhrlichia species, andone tick was PCR positive, indicating thatE.chaffeensis DNA can bedetected inticks harboring this organism, although thesensitivity may below. Humanehrlichiosis wasdescribed intheUnited States for thefirst timein1986(10). Thefirst case, a51-year-old male whoreported tickbites, subsequently becamefebrile and hadheadaches andconfusion, butnorash. Thepatient was treated withchloramphenicol andtetracycline andrecovered. Unusual inclusions werenotedinthepatient's mononuclear cells andwerelater recognized asbeing characteristic ofthegenusEhrlichia. Subsequent serologic test results