Objective To detect the positively selected sites in the surface ( S) gene of hepatitis B viruses ( HBVs) from patients with occult HBV infection and to study the molecular mechanism of occult HBV infection.Methods The sequence of S gene from patients with occult HBV infection and reference strains of eight HBV genotypes ( A through H) were downloaded from GenBank and then alignment analysis were performed by using Clustal W software .Phylogenetic trees were constructed by using MEGA 5.05 soft-ware package.PAML4.7 was used to analyze positively selected sites .Results A total of 1286 HBV se-quences from patients with occult infection were searched in GenBank .One hundred and seventy-four com-plete gene sequences encoding surface S protein were screened after alignment analysis and confirmation , of which 13 sequences with nonsense mutation were removed .The likelihood ratio test showed that for both the 161 remained sequences and the 31 reference sequences , the selection models of M2, M3 and M8 were sig-nificantly better than the neutral models of M0, M1 and M7 (2△lnL<55.12, P<0.001).By using Bayes Empirical Bayes (BEB) analysis, 14 positively selected sites (including codon 3, 8, 40, 45, 46, 47, 49, 68, 126, 127, 164, 184, 207 and 210) were detected in the surface gene of HBVs from patients with occult HBV infection, eight of which were located at the immune epitope of HBsAg .However, only 2 positively se-lected sites were identified in reference sequences .Conclusion The long-lasting persistence of HBV in pa-tients with occult HBV infection might be caused by the adaptive evolution of their surface gene in a form of escape mutant under immune suppressive condition .

Objective:To analyze the clinical characteristics of asymptomatic infection of brucellosis, in order to provide reference for prevention and treatment of brucellosis.Methods:Retrospective analysis was used to collect the clinical data of patients with brucellosis asymptomatic infection and confirmed cases admitted to the 940th Hospital of Joint Logistics Support Force of Chinese PLA from 2017 to 2021, and the demography characteristics, clinical manifestations and laboratory test results were analyzed.Results:The results showed that a total of 18 cases of asymptomatic infection and 85 confirmed cases of brucellosis were included, and there was no statistically significant difference in age, gender, occupation and ethnicity distribution between the two groups ( F = 7.09, χ 2 = 0.74, 4.02, 0.55, P = 0.295, 0.785, 0.327, 1.000). The 18 cases of asymptomatic infection of brucellosis were found through screening in key populations, and no clinical symptoms or abnormal imaging signs were observed. The clinical symptoms of 85 confirmed cases were mainly muscle and joint pain, fever, sweating, fatigue, and low back pain; and the imaging manifestations were mainly arthritis, splenomegaly, and spondylitis. The median percentage of eosinophils (0.70%, 1.40%), percentage of basophils (3.05%, 0.40%), C-reactive protein (1.62, 4.62 mg/L), erythrocyte sedimentation rate (1.00, 11.00 mm/h), and antibody titer of serum agglutination test (1 ∶ 100, 1 ∶ 200) showed statistically significant differences between asymptomatic infection and confirmed cases of brucellosis ( Z = - 2.97, - 5.11, - 3.49, - 3.21, - 3.50, P = 0.003, 0.001, 0.001, 0.001, 0.007). Conclusions:There is a difference in the composition of granulocytes between asymptomatic infection and confirmed cases of brucellosis, and the level of inflammatory response indicators is lower than that of confirmed cases. Regular seroepidemiological surveys among key populations can help screen for asymptomatic infection of brucellosis.