Biomedical subjects
Publications and source records attributed to Irina Golovljova.
Serum from 2 Norwegians with tickborne encephalitis (TBE) (1 of whom was infected in Denmark) and 810 Norwegian ticks were tested for TBE virus (TBEV) RNA by reverse transcription-polymerase chain reaction. Sequencing and phylogenetic analysis were performed. This is the first genome detection of TBEV in serum from Norwegian patients.
Tick-borne encephalitis virus (TBEV) is a severe problem in Estonia. In the present article the first genetic analysis of Estonian TBEV strains is described. In total, seven TBEV strains were isolated from ticks (Ixodes ricinus and I. persulcaus), rodents (Apodemus agrarius and Cletrionomys glareolus), and serum from a tick-borne encephalitis (TBE) patient. The nucleic acid sequences of the viral genome encoding almost the complete E protein (nt 41-1250) and the 3'-NCR-termini of the Estonian TBEV strains were determined by direct sequencing of RT-PCR products. The results showed that all three known TBEV subtypes, Western TBEV (W-TBEV), Far-Eastern TBEV (FE-TBEV), and Siberian TBEV (S-TBEV), co-circulate in Estonia. The Estonian TBEV strains of the S-TBEV and W-TBEV subtypes clustered with the previously reported strains from Latvia and Lithuania. Within the FE-TBEV subtype, however, the Estonian strain Est2546 clustered together with the strain Sofjin, originating from the Far-East of Russia, but not with the strain RK1424, isolated in the neighboring Latvia. This suggests a different evolutionary history for the Estonian and the Latvian strains in the FE-TBEV subtype. The Estonian TBEV strain (Est3535), which belonged to the S-TBEV subtype, had an organization of the 3'-NCR similar to that of strains from the Far-East of Russia (Irkutsk). The 3'-NCRs of Estonian strains of the W-TBEV subtype (Est3051, Est3053, Est3476, and Est3509) were very similar to those of the strain Ljubljana I from the Balkans. In the 3'-NCR sequence of the Estonian strain Est2546, which belonged to the FE-TBEV subtype, a deletion from position 10461 to 10810 extending approximately 10 nucleotides into the core element, was detected.
Human serum samples collected from healthy individuals in 14 counties were screened by ELISA in order to investigate the presence of hantavirus infections in Estonia. Out of 1,234 serum samples, 124 were found positive for hantavirus-specific IgG and were subsequently serotyped by a focus reduction neutralization test. A total of 112 samples neutralized at least one of the examined hantaviruses-Puumala (PUUV), Saaremaa (SAAV), Dobrava (DOBV), Hantaan, and Seoul viruses-and thereby, the focus reduction neutralization test confirmed the overall hantavirus seroprevalence rate in Estonia to be 9.1%. Most of the sera showed a specific reaction (at least 4-fold higher endpoint titer) of neutralizing antibodies to PUUV (5.1%), while 3.4% showed a SAAV- or SAAV/DOBV-specific reaction. The fact that seven sera (0.6%) could not be serotyped may indicate the presence of an unknown hantavirus serotype. Hantavirus infections were confirmed in 13 of 14 investigated counties, with highly varying seroprevalence rates (1.0-28.4%). The sex ratio was 1.8:1.0 (M:F), and the antibody prevalence peaked in the age group 45-54 years. A total of 513 rodents of seven species trapped in seven counties were examined for the presence of hantavirus antigen, in order to study the distribution of hantavirus natural carriers. Two species, Clethrionomys glareolus and Apodemus agrarius, were found positive for hantaviral antigen in 13.7% and 4.5% of the investigated rodents, respectively. Analyses of viral sequences recovered from infected C. glareolus tissue samples showed that the infecting virus belonged to the PUUV genotype, confirming that PUUV circulates in mainland Estonia. The Estonian PUUV strains were placed in the closest proximity to Russian PUUV strains in phylogenetic trees, suggesting a common evolutionary history. Together with earlier data on SAAV in A. agrarius, the results revealed that two hantaviruses, PUUV and SAAV, are common in Estonia and that the incidence of human infection is high in both cases.