Investigation of 9 pathogenic intracellular bacteria in blood samples from outpatients with undefined febrile illness

  Objective  To investigate and evaluate 9 intracellular pathogens in blood samples from outpatients with undefined fever via a TaqMan PCR array.

  Methods  The primer-probe-sets for the TaqMan PCR array were targeted to conserved genus-specific genes including 17 kDa gene of Rickettsia, 47 kDa gene of Orientia, dsb of Ehrlichia, msp2 of Anaplasma, 23S rRNA of Coxiella, omp1 of Chlamydia, ssrA of Bartonella, ISFtu2 of Francisella tularensis and bcsp31 of Brucella. Reaction parameters and specificity for each TaqMan PCR were optimized and tested. The array was performed to detect pathogens described above in blood samples collected from patients with undefined febrile illness in the capital areas of Inner Mongolia from March to December in 2021.

  Results  The TaqMan PCR array enable to simultaneously screen 9 pathogens in the blood sample with a high specificity and with a decent tolerance to background DNA from host. Out of 335 blood samples from undefined febrile illness, 10.75% (36/335) were detection positive, including 23 (6.87%) of Anaplasma, 10 (2.99% ) of Rickettsia and 3 (0.90% ) of Brucella. The rest targeting pathogens in the array were tested all negative. Rickettsia positive samples were further verified by nested PCR and amplicon sequencing. Phylogenetic analysis revealed the causative rickettsial agent was closely related to Rickettsia sibirica. Among the undefined febrile patients, male farmer and herdsmen between 40−79 years old who often exposure to animals are at the high risk of anaplasmosis, rickettsiosis and brucellosis.

  Conclusion  The preliminary results suggest the main pathogenic intracellular bacteria in patients with undefined fever, especially male farmer and herdsmen aged 40−79, are likely Anaplasma, Rickettsia and Brucella in centre-western Inner Mongolia region. Physicians and health administration department should be alerted to the threats of these intracellular pathogens on the local population.