Biomedical subjects

G F Gao

Publications and source records attributed to G F Gao.

23 records · Page 2Linked to original sources

PubMed1995

An arbovirus cline across the northern hemisphere.

The mode and tempo of arbovirus evolution and dispersal can help to explain the dynamics of pandemics, viral outbreaks, and emerging viruses. By comparing nucleotide and deduced amino acid sequences of their envelope proteins, we describe the continuous distribution of the tick-borne encephalitis (TBE) complex viruses, the most important flaviviruses in Europe, across major geographical areas and the conditions under which mutations occur. The analyses reveal a correlation between the geographical and genetic distances of these viruses. The arthropod host appears to be a key factor for the formation and maintenance of this cline by constraining TBE dispersal and evolution. This is also illustrated by comparisons with mosquito-borne flaviviruses.

Animals↗

PubMed1995

The virus causing encephalomyelitis in sheep in Spain: a new member of the tick-borne encephalitis group.

The nucleotide and deduced primary amino acid sequence of the envelope gene of two virus isolates from the brains of Spanish sheep with encephalomyelitis, were determined and compared with those of other flaviviruses. The amino acid alignments showed that the Spanish viruses shared 95 to 96 per cent homology with the envelope protein of louping ill virus and western European tick-borne encephalitis virus. In comparison, the maximum variation in amino acid identities among strains of louping ill virus from the British Isles is 1.8 per cent. The Spanish isolates were distinguishable from all other known flaviviruses by the presence of a unique tripeptide sequence (AQR) at amino acid positions 232 to 234 in the E protein, the position at which a genetic marker for distinct flavivirus species has been identified. Other genetic markers, viz DSGHD (amino acids 320 to 324) and EHLPTA (amino acids 207 to 212), which identify the tick-borne encephalitis group within the genus Flavivirus, were present in the amino acid sequences of the Spanish virus. It is concluded that the cause of sheep encephalomyelitis in Spain is a distinct species in the tick-borne encephalitis virus group.

Animals↗

PubMed1994

Identification of naturally occurring monoclonal antibody escape variants of louping ill virus.

Louping ill virus isolates from Great Britain, Ireland and Norway were compared antigenically by indirect immunofluorescence, haemagglutination-inhibition and neutralization tests using a panel of five envelope-specific and five non-structural protein NS1-specific monoclonal antibodies raised against louping ill virus. The viruses were grouped according to their reactivities with the antibodies. Group 1, members of which were isolated between 1931 and 1987, consisted of 13 viruses that reacted with all antibodies, whereas group 2, members of which were isolated after 1980, consisted of five viruses that were positive with only eight of the 10 monoclonal antibodies. The two monoclonal antibodies that did not react with the group 2 viruses are known to be neutralizing antibodies and the amino acids that they recognize in the viral envelope protein have been identified. We therefore refer to the group 2 viruses as naturally occurring monoclonal antibody escape variants. When compared with group 1 viruses, the escape variants showed reduced virulence for mice in terms of the time taken to kill and/or the proportion that died, following intraperitoneal inoculation. The nucleotide and deduced amino acid sequences of the envelope gene of one escape variant were compared with those of several group 1 viruses. A single amino acid substitution at residue 308 was detected in the envelope protein of the escape variant which corresponds precisely to the position in experimentally selected attenuated monoclonal antibody escape mutants. The importance and potential implications of these naturally occurring variants in louping ill epizootiology and vaccine-based control are discussed.

Animals↗

PubMed1993

Classification of a new member of the TBE flavivirus subgroup by its immunological, pathogenetic and molecular characteristics: identification of subgroup-specific pentapeptides.

The antigenic, pathogenic and molecular characteristics of Turkish sheep encephalitis (TSE) virus, strain TTE80, were compared with other members of the tick-borne encephalitis (TBE) virus complex. Monoclonal antibodies with defined specificity for the flavivirus envelope glycoprotein distinguished TSE virus from louping ill (LI), western or far eastern TBE, Langat and Powassan virus in indirect immunofluorescence, haemagglutination-inhibition and neutralization tests. On the other hand, TSE virus, which produces an LI-like disease in sheep, resembled LI virus in mouse neurovirulence tests. Molecular homology data of all the structural genes of TSE virus compared with other tick-borne flaviviruses demonstrated that TSE virus is a distinct member in the TBE virus subgroup. The data are consistent with the conclusion that TSE virus has evolved by a separate evolutionary pathway as compared with the close antigenic relatives, western European, far eastern TBE viruses and LI virus. By aligning the encoded amino acids in the viral envelope glycoprotein of mosquito- and tick-borne flaviviruses, we have also identified subgroup-specific pentapeptide motifs for the tick-borne encephalitis, Japanese encephalitis and dengue subgroup viruses of the genus Flavivirus. These pentapeptides have important implications for the evolution, classification and diagnosis of flaviviruses.

Amino Acid Sequence↗

PubMed1993

Sequencing and antigenic studies of a Norwegian virus isolated from encephalomyelitic sheep confirm the existence of louping ill virus outside Great Britain and Ireland.

We have carried out an antigenic analysis and nucleotide sequence comparison of the envelope glycoprotein of recognized louping ill virus strains isolated from Scotland with that of a Norwegian virus known to cause encephalomyelitis in sheep. Monoclonal antibodies with defined specificity for the louping ill virus envelope glycoprotein failed to distinguish between the Norwegian virus and prototype louping ill virus in indirect immunofluorescence, haemagglutination inhibition and neutralization tests. Nucleotide sequencing of the envelope glycoprotein and alignment of the deduced amino acid sequence with other known sequences revealed that the Norwegian virus closely resembles (> 95% identity for nucleotide and > 98% identity for amino acid sequences) louping ill virus. Maximum variation in identities among four strains of louping ill virus were 4.4% and 1.8% respectively for nucleotide and amino acid alignments. We conclude that sheep encephalomyelitis in Norway is caused by louping ill virus. These results imply that other viruses present in Europe and known to cause encephalitis/encephalomyelitis of sheep could be caused by louping ill virus.

Animals↗