Construction And Observation Of Infection Model In Rabbits Of Clinical Treponema Pallidum Strains

Background: Syphilis is a sexually transmitted infection(STI)caused by Treponema pallidum(Tp)which does great harm to humans.Tp can invade the body tissues and organs,or lead to stillbirth,miscarriage,premature delivery and fetal syphilis by the placenta.At present,syphilis is widely spread around the world and has become one of the important social public health problems.Humans are the only natural reservoir for the subspecies pallidum.Tp is characterized by a small genome that lacks the ability to encode sufficient metabolic pathways necessary to make most of its macronutrients and it must rely on its hosts.It is difficult to culture continually in vitro,so the approach to study the organism is limited.It is reported that Tp can be proliferated in apes,mice and rabbits and rabbit is the best animal to construct the model of syphilis.It has been used to clarify the pathophysiology and related influencing factors of syphilis rabbits at various stages after vaccination,which is of great significance to the pathogenesis,diagnosis,drug treatment and prognosis of syphilis.Objective: To construct animal model of clinical Treponema pallidum strain.To observe the serological changes and clinical manifestations of the syphilis rabbit infection model.Methods: From March 2018 to February 2019,clinical syphilis specimens were collected from the Department of Stomatology,Shandong Provincial Dermatology Hospital,and the suspension was prepared.The suspension was injected into the testes of New Zealand male rabbits.The changes of rabbits were observed dynamically and syphilis serum was checked weekly.The successfully infected syphilis rabbit model was sacrificed and the Tp strain was isolated.The fresh Tp strain isolated was tested for Tp content,partially passaged,and the remainder was frozen.Results: In this study,6 clinical strains of Treponema pallidum were successfully isolated,of which 5 strains were successfully inoculated,namely A,C,D,E and F strains.The rabbit models of A,C,D,E and F strains were transected with TPPA on the 28 th,7th,14 th,32th,and 35 th day after inoculation.The rabbit model of the A strain of syphilis was reversed on the 35 th day of inoculation and the rabbit model of D,E and F strains showed positive serum TRUST after 42 days of inoculation,and the titer increased first and then decreased after time.In the rabbit model,testicular swelling was found,and the scrotum on one side of the D strain rabbit model showed ulceration.The inoculated A strain was continuously passed for 3 generations,and testicular swelling began to appear on the 6th day after inoculation.TPPA was converted to positive on the 7th,9th,and 7th day after inoculation,and the average time was 7.7 days.The frozen test strains were slightly swollen on the 12 th day after inoculation,TPPA positive on the 14 th day,and TRUST positive on the 35 th day,the titer was 1:4.The long-term test found that the titer did not change.When the TRUST titer of the syphilis rabbit model was in the ascending phase,the A strain was isolated.When the TRUST titer decreased,the strains C and D were isolated,and the bacterial suspension was prepared.The quantitative analysis of Tp nucleic acid showed that the strain A had the highest bacterial count,and the strains of C and D were relatively high.Conclusion: The clinical strain of Treponema pallidum can be successfully isolated and preserved by rabbit testicular inoculation method.Testicular swelling and ulceration occurred after successful inoculation of clinical Tp strains,syphilis serological conversion to positive,and there were individual differences in the time of occurrence.The TPPA conversion time is earlier than TRUST,and the TRUST titer is generally rising,stable,and decreasing.Compared with the original strain rabbit model,the testicular swelling and TPPA conversion time were earlier and stable,and there was no significant difference in the time of TRUST.When the testicular swelling is obvious and the TRUST titer is in the ascending phase,the testis can be separated to obtain a high concentration of the bacterial suspension.