长角血蜱经卵传播斑点热群立克次体新基因型Candidatus Rickettsia longicornii的研究

Transovarial transmission of a new genotype Candidatus Rickettsia longicornii of spotted fever group Rickettsia in Haemaphysalis longicornis

目的确认长角血蜱是否具有经卵传播斑点热群立克次体(Spotted fever group rickettsia,SFGR)新基因型Candidatus Rickettsia longicornii的能力。方法采集牛体表饱血长角血蜱,在实验室诱导产卵,并采用聚合酶链式反应检测蜱卵中Candidatus R. longicornii核酸。扩增长角血蜱母体和蜱卵中Candidatus R. longicornii基因序列,分析同源性和遗传进化关系。结果共采集55只饱血长角血蜱(雌性成蜱),检测Candidatus R. longicornii核酸,21只阳性,阳性率为38.18%。共收集约2 500只长角血蜱蜱卵,分成50组检测Candidatus R. longicornii,6组阳性,蜱卵最低感染率为0.24%。经同源性分析,长角血蜱母体和蜱卵Candidatus R. longicornii基因序列与首次在韩国发现的蜱源ROK-HL727株Candidatus R. longicornii基因序列同源性均达到99.79%以上。母体和蜱卵2个Candidatus R. longicornii基因序列间同源性达到99.69%以上,在系统进化关系上均与ROK-HL727株基因序列处于同一个分支,且遗传关系较近。结论长角血蜱母体SFGR Candidatus R. longicornii基因型感染率较高,且可经卵传播该基因型。

Objective To investigate whether Haemaphysalis longicornis can transovarially transmit the spotted fever group Rickettsia(SFGR) new genotype Candidatus Rickettsia longicornii. Methods Feeding H. longicornis was collected from cattle body surfaces and induced to oviposit in the laboratory. The polymerase chain reaction was used to detect the nucleic acid of Candidatus R. longicornii in tick eggs. The gene sequences of Candidatus R. longicornii in the mothers and eggs of H. longicornis were amplified. An analysis was performed on the homology and phylogenetic relationship. Results A total of 55 feeding H. longicornis(adult female ticks) were collected, among which 21(38.18%) were positive for Candidatus R. longicornii according to the nucleic acid test. About 2 500 H. longicornis eggs were collected and divided into 50 groups, of which 6 groups were positive for Candidatus R. longicornii. The minimum infection rate was 0.24% in tick eggs. The homology analysis showed that the gene sequences of Candidatus R.longicornii from H. longicornis mothers and eggs had more than 99.79% homology with that of the tick-derived ROK-HL727 strain first found in South Korea. The Candidatus R. longicornii gene sequence homology between H.longicornis mothers and eggs was over 99.69%;the gene sequences were in the same branch and had close phylogenetic relationships with that of the ROK-HL727 strain. Conclusion The infection rate of H. longicornis mothers with the SFGR Candidatus R. longicornii genotype is relatively high, and the genotype can be transovarially transmitted.