Coxiella burnetii infection in a patient did not involve tick bite

Abstract Background: Coxiella burnetii that causes Q fever in humans is transmitted through contaminated aerosols or consumption of raw milk from infected animals. Ticks are known to be vectors of C. burnetii, but their role in human infection is still controversial. Method: In this study, an epidemiological investigation was conducted on a 60-year-old man hospitalized with fever. Polymerase chain reactions (PCRs) were performed on the blood sample of the patient and the four ticks collected from the patient to diagnose vector-borne infectious diseases. Indirect immunofluorescence assays (IFAs) were performed on the serum sample to detect IgG and IgM antibodies specific to Q fever, spotted fever, Lyme disease, and anaplasmosis. Results: The ticks collected were identified as adult female Haemaphysalis longicornis. All PCRs performed on blood specimens yielded negative results, except for the Coxiella sp.-specific 16S rRNA nested PCR (N-PCR). Coxiella 16S rRNA N-PCR and sequencing results confirmed the presence of C. burnetii. IFA results indicated that the serum sample showed ≥ 4-fold increase in both IgM and IgG antibody titers against Q fever. PCR results were positive only for three ticks and showed the presence of C. endosymbiont. The phylogenetic tree showed that ticks had Coxiella-like bacteria and the patient had C. burnetii. The ticks carrying Coxiella-like bacteria were Haemaphysalis symbionts. Conclusions: Even though the patient and ticks were all positive to Coxiella sp.-specific 16S rRNA N-PCR, since different bacterial species were isolated from the patient and the ticks, we concluded that he was not infected with C. burnetii through tick bites.