环泰山区域恙虫病东方体感染状况调查及基因序列分析

A study of Orientia tsutsugamushi infection in the area surrounding Mount Tai and gene sequence analysis

目的了解环泰山区域恙虫病东方体(Ot)感染情况,确定是否存在恙虫病疫源地。方法应用PCR技术和血清学等方法调查泰山西南麓、东南麓部分村庄及泰山景区人、鼠Ot感染情况,病人发病情况采用个案表调查。结果血清抗-Ot8例现症病人全部阳性,14例既往病人4例阳性,均为Gilliam型;115名健康人抗-Ot阳性率为8.70%,发病区域和无发病区域分别为26.92%和3.37%,差异有统计学意义(P<0.05)。PCR检测Ot基因,4份病人焦痂3份阳性,100份鼠脾,4份阳性,其中黑线姬鼠3份,小家鼠1份。序列同源性分析和系统发生树分析显示,2份阳性鼠标本的PCR产物核苷酸序列完全相同,与Sdu-1型的核苷酸序列同源性为99.77%,与Kawasaki型的同源性为95.74%。另2份阳性鼠标本的核苷酸序列与TA686型的同源性分别为86.27%和77.11%。病人发热、皮肤焦痂或溃疡发生率较高,达98.08%和92.31%。结论环泰山区域人、鼠间均存在Ot自然感染,恙虫病自然疫源地已经形成,病人集中出现在每年的9～11月,10月份为主要发病月,属典型的秋冬型疫源地;宿主动物呈非单一性,黑线姬鼠为Ot的主要储存宿主;人群中存在Ot隐性感染;Ot血清型为Gilliam型,基因型Kawasaki相似型为流行株,鼠间还存在TA686型相似株,呈基因多样性倾向。

Objective To ascertain the prevalence of Orientia tsutsugarnushi （Ot） infection in the area surrounding Mount Tai and determine the existence of endemic loci of tsutsugamushi disease. Methods PCR and serology techniques were used to investigate the incidence of infection among rats in the villages at the southwest and northwest foot of Mount Tai and scenic sites, and a questionnaire was used to investigate that incidence among patients. Results Eight patients were positive for serum anti Ot antibodies. Four 4 of 14 patients with a previous history of the infection were positive for antibodies and all 4 had the Gilliam strain of Or; 115 healthy individuals were positive for anti-Ot antibodies at a rate of 8.70%. Incidence in epidemic areas and non-epidemic areas was 26. 92% and 3. 37%, respectively, and the difference in incidence rates was statistically significant（P〈0.05）. Three eschars from 4 patients were positive for Ot as detected by PCR. Four of 100 mouse spleen specimens were positive; of these, 3 were specimens from Apodemus and 1 was from Mus musculus. Further homological analysis and phylogenetic tree analysis of positive mouse samples revealed that the nucleotide sequences of PCR products from two specimcns were identical and had a homology of 99.77% with the Sdu-1 strain of Ot and 95.74% with the Kawasaki strain of Or. Nucleotide sequences of 2 other specimens had a homology of 86. 27% and 77.11%, respectively, with the TA686 strain of Or. Patients with a fever and esehars or ulceration had a high incidence of up to 98.08 % and 92.31 %, respectively. Conclusion Ot natural infection exists in humans and rats in the area around Mount Tai, and natural foci of tsutsugamushi disease have formed. Patients are concentrated primarily in September to November, with the greatest incidence in October, so the focus of infection is typically autumn and winter. Many host animals carry the infection, and Apodemus is the main reservoir host. A latent Ot infection was noted among the human population. Ot infection was identified as the Gilliam serotype and the prevalent strain of Ot had a genotype similar to the Kawasaki strain. A strain similar to the TA686 strain was noted among mice and was genetically di verse. The TA686 strain was first discovered in Shandong Province. The rate of Ot detection is higher in eschar specimens from patients and eschar specimens are easy to collect, so eschars from patients can be used in place of other specimens to study the pathogens responsible for Tsutsugamushi disease.