High prevalence of Rickettsia spp. in ticks from wild hedgehogs rather than domestic bovine in Jiangsu province, Eastern China

Abstract

Background: Spotted fever group Rickettsia (SFGR), containing various pathogenic Rickettsia spp., poses remarkable negative influences to public health by causing various severe or mild diseases. Information regarding prevalence of SFGR in ticks in Jiangsu province, Eastern China, is still limited and needs urgent investigations.

Methods: Hedgehog- and bovine-attached ticks were collected from Jiangsu province, Eastern China. DNA of individual ticks was extracted for nested polymerase chain reaction amplifications targeting gltA, 16S ribosomal RNA (rrs), ompA, ompB, and sca4 genes following with sequencing. SFGR-specific IgG antibodies in sera of local donators were evaluated using ELISA.

Results: Overall, 144 (83.2%) of the 173 ticks from hedgehogs and 2 (1.2%) of the 168 ticks from bovine were positive for one of the three identified Rickettsia spp., with significant difference between the two groups (P = 3.6e-52). Candidatus Rickettsia principis (9; 5.2%) and R. heilongjiangensis (135; 78.0%) were detected in Haemaphysalis flava rather than in H. longicornis ticks from hedgehogs. R. heilongjiangensis (1; 0.6%) and Candidatus R. jingxinensis (or Candidatus R. longicornii) (1; 0.6%) were identified in H. longicornis and Rhipicephalus microplus ticks from bovine, respectively. Phylogenetic analysis indicated Candidatus R. jingxinensis belonged to R. japonica subgroup, whereas Candidatus R. principis belonged to a novel subgroup. Higher serological prevalence of spotted fever and SFGR-specific IgG antibody level in humans were observed around the investigated area than in urban areas, without significant difference.

Conclusion: Candidatus R. principis and Candidatus R. jingxinensis were identified in Jiangsu province, Eastern China, and fully genetically characterized for the first time. The higher prevalence of SFGR in hedgehog-attached ticks as well as the higher SFGR-specific IgG antibody level and seropositive rate in humans around the investigated area suggested that more attention should be paid to SFGR. This pathogen is usually transmitted or harbored by wild animals and ticks. This study provides important epidemiological data for both physicians and public health officers in developing early prevention and control strategies against potential Rickettsia infections and in the preparation of suitable testing and treatment needs for rickettsiosis in the endemic areas.

Keywords: Candidatus Rickettsia jingxinensis; Candidatus Rickettsia principis; Rickettsia heilongjiangensis; hedgehog; spotted fever group Rickettsia; tick.

Figure 1

Sample collection sites and the observed tick hosts. (A) Locations of tick (yellow dot) and sera (red and yellow dots) collection sites; (B) a parasitic tick collected from an already dead hedgehog; (C) bovine hosts for tick collections; (D) a farmer bitten by a tick observed during our sample collection.

Figure 2

Haemaphysalis spp. and Rhipicephalus microplus ticks collected in this study.

Figure 3

Phylogenetic tree of Rickettsia spp. based on a concatenated sequence of gltA, rrs, ompA, ompB, and sca4 gene sequences. The phylogenetic tree was generated with MEGA 7.0 software using the maximum likelihood method with 1,000 replicates for bootstrap testing. Bootstrap values > 50% are shown. The scale bar indicates nucleotide substitutions per site. The GenBank accession numbers of the reference sequences are indicated. The newly obtained sequences are indicated with black dots.

Figure 4

Box and whisker plot of OD450 values of the serum samples detected using ELISA. The box represents 25th to 75th percentile and the mean value (line in the middle of each box), and whisker shows the minimum and maximum values. The sampling locations were indicated. n.s., not significant.