K. Shiraishi et al., Genetic analysis, of an influenza B virus isolated from a patient with encephalopathy in Japan, J MED VIROL, 65(3), 2001, pp. 590-597
An influenza B virus, B/Saga/S172/99 (SAG99), was isolated from the nasopha
rynx of a patient with encephalopathy/encephalitis in Japan in 1999. To cla
rify the molecular characteristics of this virus, detailed analysis of the
gene segments coding for the hemagglutinin (HA), neuraminidase (NA), nucleo
protein (NP), matrix protein (M) and non-structural protein (NS) was undert
aken. All five genes of SAG99 showed high nucleotide and predicted amino ac
id similarities with those of recent non-encephalopathic strains isolated i
n the same epidemic season. Subsequent phylogenetic analysis revealed that
all five gene segments of SAG99 analyzed in the present study were most sim
ilar to those of the recent Yamagata/16/88-like viruses. The hemagglutinin
and neuraminidase proteins of SAG99 were each distinguished from those of r
ecent epidemic strains by one characteristic amino acid substitution. These
substitutions were not found in the previously reported encephalopathy/enc
ephalitis-derived influenza B viruses, and we could not find any common cha
racteristic amino acid, changes in SAG99, and these viruses. Similarly, amo
ng the internal proteins studied, only the M2 protein of SAG99 was found to
contain a single novel amino acid change when compared with other recent i
solates. Thus, it was apparent that SAG99 contained very few amino acid dif
ferences when compared: with other epidemic viruses. The association of rec
ent B/Yamagatal 16/88....like viruses with encephalitis/encephalopathy obse
rved in the present study and, previously suggest that these viruses may ha
ve a, higher potential for causing neurological complications in certain in
dividuals. (C) 2001 Wiley-Liss,inc.