Current Trends Antigenic Analysis of Recent Influenza
Virus Isolates
Most influenza virus isolates recovered in the United States
and
Europe during the winter of 1982-1983 have been type A(H3N2)
strains
closely related to A/Bangkok/1/79. This was consistent with
increased
activity of such strains in the Southern Hemisphere and several
tropical Asian countries during July and August 1982 (1). Type
A(H3N2) influenza strains continued to be isolated in Asia during
late
1982 and early 1983, with sporadic cases in Hong Kong (September),
localized outbreaks or moderate epidemics in Japan (February),
Korea
(December), Pakistan (January), People's Republic of China
(December),
Taiwan, Province of China (January), Singapore (October), and
Thailand
(October).
Antigenic analysis of isolates from some Asian countries
identified a trend toward a predominance of strains, which, in
hemagglutination inhibition (HI) tests with ferret antiserum,
differ
from A/Bangkok/1/79 or other recent variants. Such strains, called
A/Philippines/2/82, were named for the prototype of a series of
strains first identified during an outbreak in the Philippines in
summer 1982. As shown in Table 1, although antiserum to
A/Philippines/2/82 reacts as strongly with A/Bangkok/1/79 as with
its
homologous antigen, A/Philippines/2/82 antigen is poorly inhibited
by
the A/Bangkok/1/79 serum.
Antigenic analysis of influenza viruses from Europe and North
America examined during the 1982-1983 winter has confirmed the
presence of A/Philippines/2/82 virus in these regions, although the
predominant strains have been well inhibited by A/Bangkok/1/79
serum.
By February, up to 20% of isolates in the United Kingdom were
identified as similar to A/Philippines/2/82 in HI tests with ferret
antiserum, although Philippines-like strains had been absent
earlier
in the season. They have also been identified in Belgium,
Czechoslovakia, Italy, and the Netherlands. In North America,
A/Philippines/2/82-like strains were first isolated in Florida and
Manitoba, Canada, in January 1983, and, as of April, had been
identified in Connecticut, Georgia, Missouri, New Mexico, New York,
Ohio, and Oklahoma. Other H3N2 variants, such as A/Texas/1/77-like
strains, A/Bangkok/2/79-like strains, and A/Shanghai/31/80-like
strains (Table 1), have also been identified among recent isolates
from Asia, Europe and North America.
Antigenic analysis of influenza A(H1N1) and influenza B strains
isolated in recent months continues to show their close similarity
to
A/England/333/80 and B/Singapore/222/79 strains that have
circulated
in the preceeding recent influenza seasons.
Reported by Virus Disease Unit, World Health Organization, Geneva;
WHO
Collaborating Center for Influenza, Influenza Br, Div of Viral
Diseases, Center for Infectious Diseases, CDC.
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