Genetic Diversity Of Chlamydia Spp. Infection In Sheep And Goat Flocks In Northwest China

Chlamydia spp.are a group of gram-negative,obligate intracellular bacteria with unique biphasic development cycles.They can infect both humans and animals causing a variety of diseases.In 1970 s,outbreaks of Chlamydia-related abortion in sheep was first reported in Qinghai province,China.Since then,Chlamydia infection caused abortion in animals including in sheep,goats,swine and cattle has been widely reported in many provinces,across China.However,previous studies mainly focused on serological investigation or case reports,and national-or regional-wide molecular epidemiology investigation is still lacking.Therefore,scarcity of knowledge on Chlamydia spp.prevalence in livestock has limited the development and implementation of preventive measures against Chlamydia-related diseases in China.This study aimed to investigate the prevalence of Chlamydia spp.in sheep and dairy goats in northwest China.Vaginal swabs,rectal swabs and aborted fetuses were collected,and the presence of Chlamydia was detected by PCR followed by sequencing.Chlamydia strains were further isolated from the positive samples.In addition,the coding sequence of chlamydial protease like activity factor(CPAF)of C.abortus was cloned and inserted into a prokaryotic expression vector.In order to establish a potential detection antigen for diagnosis of C.abortus,we have attempted to express this recombinant protein in E.coli.The main findings are shown here.1.The infection rate of Chlamydia spp.is higher in sheep flocks in northwest China.C.abortus and C.pecorum are the two major species in sheep flocks with similar infection rates of 64.9% and 60.94,respectively.C.psittaci is rarely detected.The prevalent strains of C.abortus in sheep are ST150 and MLVA 2 genotypes,representing genetic conservation.In contrast,the prevalent strains of C.pecorum show high genetic diversity,with three ompA genotypes.Consideration of the pathogenicity,C.abortus might be the main pathogenic chlamydial strain causing abortion in sheep in northwest China.2.Infection of C.abortus and C.pecorum is common in dairy goats in Guanzhong region,Shaanxi province.The prevalence rate of C.abortus is higher than that of C.pecorum.The genotypes of C.abortus strains prevalent in dairy goats are same as those in sheep flocks,which is also considered as the main causal agent of goat abortion.Similarly,the prevalent strains of C.pecorum also show high genetic diversity with three ompA genotypes,which differ from those in sheep flocks.3.The full-length gene coding CPAF was cloned and the recombinant protein was successfully expressed in prokaryotic expression system.The recombinant CPAF showed strong reactiongenicity with C.abortus positive serum,and thus it could be used as a potential antigen for serological tests of C.abortus infection.Taken together,our results have shed new light on the genetic diversity and pathogenicity of chlamydial pathogens in sheep and goats in northwest China.This research will also provide guidance for the diagnosis,prevention and control of animal chlamydosis in this region.