Molecular evidence of Rickettsia canadensis in ticks, Hebei, China

Abstract

China was affected severely by tick-borne rickettsiosis, and more than 10 Rickettsia species pathogenic to humans have been identified. In recent years, several Rickettsia members, with unknown pathogenicity, firstly identified abroad have been found in China. In this study, parasitic and questing ticks were recovered from two sampling sites in Hebei, China. Specific primers targeting outer membrane protein B (ompB) gene were designed to test the presence of Rickettsia canadensis by nested Polymerase Chain Reaction (PCR). As a result, a total of 428 ticks, including 232 ticks (including 230 Haemaphysalis longicornis and two H. japonica) from Laiyuan County and 196 (H. longicornis) from Luanping County, were collected. Sequencing of PCR products with the expected size and subsequently BLAST showed that 38H. longicornis ticks tested positive for R. canadensis, with an overall positive rate of 8.8%. In addition, 800-bp ompB gene and nearly complete citrate synthase (gltA) gene were recovered from six randomly selected positive samples to better understand their genetic characteristics. Nucleotide identity and phylogenetic analyses showed that R. canadensis presented geographical clustering with evidence that variants identified in the current study presented closer genetic relationship with others identified in Asian than those found in North America. In addition, epidemiological data suggested that H. longicornis may be the competent vector, and more attention should be paid to R. canadensis due to its zoonotic potential. In sum, R. canadensis was confirmed to be present in Hebei Province, China, and its surveillance in ticks should be strengthened due to potential pathogenicity, higher positive rate in ticks and wide distribution of possible vector tick species.

Keywords: Haemaphysalis longicornis; Rickettsia canadensis; gltA; ompB.