RESULTS OF GENOTYPING HEPATITIS VIRUS B IN HBsAg-NEGATIVE BLOOD DONORS IN ASTANA, KAZAKHSTAN
Authors: Ostankova Yu. V. , Semenov A. V. , Burkitbayev Z. K. , Savchuk T. N. , Totolian A. A. 
Published: January 2018

The prevalence of HBV infection is estimated by the frequency of occurrence of HBsAg and varies depending on the geographic region. Chronic infection is characterized by a stable presence of HBsAg for 6 months, with the exception of the occult form of the disease, characterized by the absence of HBsAg, an extremely low level of HBV DNA in the blood serum. The problem of identifying occult HBV (ocHBV) is especially relevant because of the development of transplantology and transfusiology. However, serological screening of donor blood used in the Russian Federation and Central Asian countries does not reveal HBV seronegative donors. Since HBV infection is possible with the introduction of small doses of the virus, the importance of using complex molecular methods for detecting donor ocHBV is obvious, despite the low viral load, since donor blood is used predominantly in patients with severe course of various diseases characterized by increased susceptibility to HBV because of immunosuppression. The aim of our work was to study the characteristics of the genetic structure of the ocHBV in donors in Astana, Kazakhstan. A total of 500 blood plasma samples from HBsAg-negative donors were obtained in 2012 from residents of Kazakhstan, Astana. Using the method, we proposed to detect HBV DNA with a low viral load, HBV was detected in 9.4% of donors. Serological markers were found in 12.7% of patients with HBV DNA, 8.5% had HBcor IgG antibodies, 4.2% had HBcor IgG and HBe IgG antibodies at the same time. Thus, in 41 (87.3%) of the blood donor, ocHBV was seronegative. Based on the phylogenetic analysis of the 47 isolates showed that the HBV of genotype D (95.75%) prevails in the examined group in comparison with HBV of genotype A (4.25%). HBV subgenotypes are represented in the following ratios: D1 — 46.8%, D2 — 17.05%, D3 — 31.9%, A2 — 4.25%. In a comparative analysis, the distribution of HBV subgenotypes in the group with ocHBV and in the case of the manifest form in donors in the Republic of Kazakhstan significantly differed — χ2 = 14.027 at p = 0.0072, df = 4. The incidence of HBV D3 with ocHBV (31.9%) exceeded that of patients with a manifest form (7.4%). The relative risk of occult form of disease in patients with the subgenotype D3 is significantly higher (RR = 1.572, CI: 1.179–2.096, p = 0.0208). When assessing the picture of HBV diversity on the material of the group including HBsAg-negative and HBsAg-positive blood donors, it is evident that the genetic relationship of the manifestations of the manifest HBV and the ocHBV of genotype D is obvious. Among the isolates are both similar in nucleotide sequences with those previously described in various regions of Europe and Central Asia, and circulating in the territory of the Republic of Kazakhstan, which indicates an independent homologous evolution of HBV in the region. The high incidence of ocHBV among HBsAg-negative blood donors is indicative not only of the widespread prevalence of the occult form of the disease course in the population and the inadequacy for the detection of chronic HBV of conventional HBsAg and HBV DNA in the peripheral blood using commercial kits, but also the need to study the characteristics of the immune response with this form of the disease course.