Arch Virol (1998) 143: 781–787
Characterisation of an avian inﬂuenza A virus isolated from a
human – is an intermediate host necessary for the emergence of
pandemic inﬂuenza viruses?
J. Banks, E. Speidel, and D. J. Alexander
Avian Virology, Central Veterinary Laboratory (Weybridge), Addlestone, Surrey, U.K.
Accepted December 18, 1997
Summary. The partial sequencing of the internal and the neuraminidase genes
of isolate 268/96 obtained from a woman with conjunctivitis showed all seven
to have closest homology with avian inﬂuenza viruses. The entire nucleotide
sequence of the haemagglutinin gene of 268/96 had close, 98.2%, homology with
an H7N7 virus isolated from turkeys in Ireland in 1995. This appears to be the ﬁrst
reported case of isolation of an inﬂuenza A virus from a human being infected as
a result of direct natural transmission of an avian inﬂuenza virus from birds.
Pandemics of inﬂuenza A infections arise every few decades and usually have a
devastating effect on the human population. They occur as a result of “antigenic
shift” i.e. when an inﬂuenza A virus of different antigenic subtype to those present
in the population suddenly emerges. In the 20
Century there have been four
identiﬁed pandemics of inﬂuenza, beginning in 1918 caused by a virus of H1N1
subtype, 1957 due to H2N2 subtype virus, in 1968 due to H3N2 subtype virus
and 1977 due to the re-emergence of H1N1 virus.
Demonstration that the 1968 H3N2 pandemic virus differed from the H2N2
virus, present from 1957 to 1968, in the substitution of two genes, PB1 and the
important surface glycoprotein haemagglutinin (H) gene, with genes almost cer-
tainly from an inﬂuenza virus of avian origin, led to the suggestion that antigenic
shift occurred as a result of reassortment of genes in dual infections with viruses of
human and avian origin [6, 9] resulting in the emergence of viruses with sufﬁcient
genes from the virus of human origin to allow replication and spread in the popu-
lation, but with a different haemagglutinin surface glycoprotein so that the human
population could be regarded as immunologically naive. Systematic surveillance