Spotted fever group rickettsiae (SFGR) detection in ticks following reported human case of Japanese spotted fever in Niigata Prefecture, Japan

Abstract

Japanese spotted fever, a tick-borne disease caused by Rickettsia japonica, was firstly described in southwestern Japan. There was a suspicion of Rickettsia japonica infected ticks reaching the non-endemic Niigata Prefecture after a confirmed case of Japanese spotted fever in July 2014. Therefore, from 2015 to 2017, 38 sites were surveyed and rickettsial pathogens were investigated in ticks from north to south of Niigata Prefecture including Sado island. A total of 3336 ticks were collected and identified revealing ticks of three genera and ten species: Dermacentor taiwanensis, Haemaphysalis flava, Haemaphysalis hystricis, Haemaphysalis longicornis, Haemaphysalis megaspinosa, Ixodes columnae, Ixodes monospinosus, Ixodes nipponensis, Ixodes ovatus, and Ixodes persulcatus. Investigation of rickettsial DNA showed no ticks infected by R. japonica. However, three species of spotted fever group rickettsiae (SFGR) were found in ticks, R. asiatica, R. helvetica, and R. monacensis, confirming Niigata Prefecture as a new endemic area to SFGR. These results highlight the need for public awareness of the occurrence of this tick-borne disease, which necessitates the establishment of public health initiatives to mitigate its spread.

Figure 1

Tick collection sites in Niigata Prefecture. On the left the localization of Niigata Prefecture in Japan. On the right, the numbers indicate the 38 tick collection sites covering the 4 geographical areas of Niigata Prefecture: Northern (Kaetsu), Central (Chuetsu) and Southern (Joetsu) areas of Niigata Prefecture corresponds to the collection sites 1 to 13, 14 to 30, 31 to 36, respectively. Sado Island area corresponds to the collection sites 37 and 38. Maps created using the Geographical Survey Institute Map Vector from the Geospatial Information Authority of Japan (https://maps.gsi.go.jp/).

Figure 2

Phylogenetic analysis for identification of species of Rickettsiae based on 450 nucleotides of 17 kDa gene (A), 382 nucleotides of gltA gene (B), 540 nucleotides of rOmpA gene (C) and 426 nucleotides of rOmpB gene (D). Sequence were aligned by using MEGA5 software (https://www.megasoftware.net). Neighbor-joining phylogenetic tree construction and bootstrap analysis were performed according to the Kimura 2-parameter distances method. Bold-face font indicate positive samples detected from ticks in this study (shown only representative sample no. from among detected SFGR).

Figure 3

Niigata prefecture map with the sites where adult stages of Ixodes spp. were collected (Circles), and the occurrence of SFGR (filled circle: SFGR Positive sites, open circle: SFGR Negative sites). From the left, “A” corresponds to I. ovatus and Rickettsia asiatica sites; “B” corresponds to I. monospinosus and R. helvetica sites, and “C” are the I. nipponensis and R. monacensis sites. Maps created using the Geographical Survey Institute Map Vector from the Geospatial Information Authority of Japan (https://maps.gsi.go.jp/).