Arch Virol (1998) 143: 891–901
Direct sequencing of the HA gene of clinical equine H3N8 inﬂuenza
virus and comparison with laboratory derived viruses
C. P. Ilobi
, C. Nicolson
, J. Taylor
, J. A. Mumford
and J. S. Robertson
Division of Virology, National Institute for Biological Standards and Control,
Potters Bar, U.K.
Centre of Preventive Medicine, Animal Health Trust, Newmarket, U.K.
Accepted January 7, 1998
Summary. Equine inﬂuenza viruses propagated in the laboratory in alternate
hosts such as embryonated hens’ eggs or mammalian cell culture have been anal-
ysed by HA sequencing and antigenically and their sequence compared to the
original virus present in clinical material. In contrast to clinically derived human
inﬂuenza virus which generally grows in MDCK cells without change, the data
for equine inﬂuenza virus were less clear in that variants of equine virus were
derived in both eggs and cells. The study indicated that the current use of eggs for
equine inﬂuenza virus surveillance and vaccine production is entirely appropriate,
but that care should be exercised when equine inﬂuenza vaccines are produced in
eggs or on mammalian cell cultures.
We have previously reported that genetically and antigenically distinct equine
inﬂuenza viruses canbe derived in the laboratory from clinical material depending
on the substrate used for viral isolation and propagation, viz., embryonated hens’
eggs or a mammalian cell line such as Madin Darby canine kidney (MDCK)
cells (Ilobi et al. ). In order to determine which laboratory derived virus is
more representative of the natural virus present in clinical material, we have now
analysed the sequence of the HA1 gene of equine/H3 inﬂuenza virus present in
clinical specimens. This has been compared with the sequence of corresponding
isolates obtained in eggs and MDCK cells. This is the ﬁrst report on the nature of
The HA1 sequences of the viruses described in this study are available under accession
numbers AJ223192, AJ223193, AJ223194, AJ223195, AJ223196, AJ223197.
Present address: Department of Virology, ICPMR, Westmead, Australia.