Epidemiological investigation and genetic characterization of Coxiella burnetii carried by parasitic ticks in the southeastern coastal region of China.

backgroundThe pathogen of Q fever, Coxiella burnetii, can persist in the environment for yearsand it can form infectious aerosols that facilitate long-distance airborne transmission of Q fever under certain conditions. Ticks are obligate hematophagous ectoparasites with a broad host range. Accumulating evidence suggests that, within natural ecosystems, ticks may contribute to the maintenance and circulation of Coxiella burnetii among wildlife and livestock, thereby representing a potential component of its transmission cycle. In recent years, cases of Q fever have been reported in Fujian Province, southeastern China. This study aimed to investigate the prevalence and genetic characteristics of Coxiella burnetii carried by parasitic ticks in coastal and inland regions of Fujian Province.

methodsOur research team conducted tick collection work in coastal and inland areas of Fujian Province from 2011 to 2023.Ticks were collected from different hosts, and species, developmental stage, and sampling location were recorded. DNA was extracted and screened for the IS1111 gene by real-time PCR. Positive samples were further tested by nested PCR targeting the groEL gene, followed by sequencing and phylogenetic analysis (neighbor-joining). Factors associated with infection were analyzed using Chi-square tests, Fisher-Freeman-Halton exact tests, and logistic regression analysis.

resultsA total of 746 tick samples were examined, representing 5 genera and 13 identified species, with additional specimens identified only to the genus level and recorded as Haemaphysalis sp. Forty-seven samples were positive for Coxiella burnetii, with an overall positivity rate of 6.30%. The infection rate in inland areas was significantly higher than that in coastal areas (10.22% and 2.60%). The dominant tick species in inland regions was Dermacentor taiwanensis, and higher infection rates were observed in Haemaphysalis Yeni (25.00%), Ixodes sinensis (25.00%), and Amblyomma testudinarium (19.35%). In coastal areas, Haemaphysalis formosensis was the dominant tick species, and Haemaphysalis hystricis showed a higher infection rate (9.84%, 6/61). Significant differences in infection rates were observed among tick genera, hosts, and regions (P < 0.05). Logistic regression showed that regional difference was the main influencing factor; ticks distributed in inland areas were 4.258 times more likely to be infected with Coxiella burnetii than those in coastal areas (P < 0.001). Phylogenetic analysis showed that the groEL sequences from both coastal and inland samples clustered with Coxiella burnetii, and sequence variation was minimally affected by regional and host differences. Three haplotypes exist in the Fujian region, with H1 being the predominant haplotype.

conclusionThe positivity rate of Coxiella burnetii in ticks from inland areas of Fujian Province was higher than that in coastal areas. Ticks parasitizing wild animals exhibit significantly higher infection rates, suggesting that ticks may participate in natural cycles in the wild. The groEL gene sequences of tick-derived Coxiella burnetii in Fujian Province were highly homologous to those from other regions.