John R. LaMontagne Memorial Symposium on Pandemic Influenza Research
Working Group 8
Virus Transmission: Understanding and Predicting Pandemic Risk
mixing vessel
Molecular basis for interspecies transmission and pathogenesis.
Influenza A virus host range is polygenic
2-3Gal
2-6Gal2-3Gal2-6Gal
2-3Gal2-6Gal
Receptor specificity is a major factor
2-3Gal H52-6Gal H9
What we know
•Pandemic Human influenza A viruses contain
genes from the avian reservoir•1918 “Spanish” flu H1N1: avian? virus that killed >20,000,000
people.
•1957 Asian flu H2N2: reassortant between avian H2N2 and
human H1N1 -> 3 avian genes: HA, NA, and PB1.
•1968 Hong Kong flu H3N2: reassortant between avian H3N?
and human H2N2 -> 2 avian genes: HA and PB1.
•Influenza viruses that circulate in terrestrial poultry have the
potential to cross to humans (H5, H9).
•Pigs could be potential intermediate hosts.
•Evidence of H3N2 in pigs in or around 1968, with H3
having 2,3 receptor specificity (Kida et al. 1988)
What we know
•Influenza viruses that have established permanent
lineages in humans have altered receptor
specificity•H1 viruses until 1957 have dual receptor specifity,
contemporary H1 viruses bind 2,6 receptors preferentially
(Rogers et al, 1989; Matrosovich et al, 2000; Gamblin et al, 2004; Stevens et al, 2004).
•Glycosylation can affect the virus binding properties to
receptors (Aytay & Schulze, 1991).
•H3 viruses recognize 2,6 receptors almost exclusively
(some of them do not grow in chicken eggs).
•H5 and H9 viruses have altered receptor specificities
(Matrosovich et al, 1999 & 2000).
Ha et al, 2001
Stevens et al, 2004
Gamblin et al, 2004
What we know
•The internal genes limit the virus’ host range
•Some internal gene constellations limit replication and
transmission of influenza in humans (Snyder et al, 1987; Clements et al,
1992).
•A single amino acid change in PB2 (627) is responsible for
host range (Subbarao et al, 1993; Hatta et al, 2001).
•Avian; Glutamic
•Human; Lysine
•Incompatibility between polymerase genes of viruses from
human and duck origin (Hatta et al, 2002).
What we know
•The internal genes limit the virus’ host range
•Interactions between replication complex and host factors
•Interaction of NS1 with…
Human U6 snRNA…disrupts binding of U6-U2 and U6-U4 during
RNA splicing (Qi et al, 1995)
NS1-I, a human homolog of the porcine 17beta-estradiol
dehydrogenase precursor protein (Wolff et al, 1996)
PABP1 and eIF4GI (Aragon et al, 2000)
30 kDa subunit of CPSF, inhibits 3'end formation of cellular pre-
mRNAs (Nemeroff et al, 1998; Chen et al, 1999; Noah et al, 2003)
Interferes with interferon pathways (Garcia Sastre, et al, 1998 a&b; Bergmann
et al, 2000; Talon et al, 2000; Wang et al, 2000, Tumpey et al 2004)
What we know
•The internal genes limit the virus’ host range
•Interaction of the polymerase complex with…
PA and hCLE a potential transcription factor (Huarte et al, 2001)
•Interaction of NS2 with…
Nuclear export pathway (O’Neill et al, 1998; Neumann et al, 2000)
M1 (Akarsu et al. 2001)
•Interaction of NP with…
RAF-2p48/NPI-5/BAT1/UAP56 (Momose et al, 2001)
NPI-, NPI-3 (O’Neill & Palese, 1995; Wang et al, 1997)
Polymerase complex (Biswas et al, 1998)
Nuclear export pathway (Elton et al, 2001)
What we know
•Some animal species may promote the emergence
of novel influenza strains
•Quail and other terrestrial birds as potential intermediate
hosts (Makarova et al 200; Perez et al, 2003)
•Changes on the globular heads of HA and NA, as well as
changes in the internal genes modulate transmission and
pathogenicity (Hulse et al 2004)
•Presence of 2,3 and 2,6 receptors in terrestrial birds
What we do not know
•Intermediate hosts that participate and the
molecular features that render a virus potentially
pandemic•The host that resulted in the emergence of the 1918, 1957,
and 1968 pandemic viruses.
•If pigs were really involved in the emergence of each one of
these pandemics.
•Circumstancial evidence of H1N1 in pigs in 1918
•No evidence of H2N2 in pigs prior, during, or after the
1957 pandemic
What we do not know
•How the known interactions with host factors
modulate virus replication in different species
•If additional interactions exist with other cellular
factors that may promote host restriction
•The exact molecular mechanism for incompatibility
among some replication complexes from different
species
•Whether different animal species favor certain
molecular changes during adaptation
What we do not know
•Whether alteration in receptor specificity is
required to jump to other species, including
humans
•Whether any of the known interactions with the
internal proteins are involved in host range
What needs to be done
•Hypothesis: Pandemic influenza is the result of a
complex process involving an expansion of the
host range of one or more avian influenza viruses
followed by a contraction with selection of one
strain that transmits readily in humans.
•Identify molecular changes associated with adaptation in
different animal species
•Classical virology and reverse genetics are instrumental to
accomplish this goal.
What needs to be done
•Changes associated with adaptation of influenza
viruses to terrestrial birds and other potential
intermediate hosts.
•Are pathways of adaptation in different animal species
ramdom?
•Or is there a pattern of changes that are more favored
than others?
What needs to be done
1. What further studies are needed to define the genetic loci
important for virus transmission between species?
2. What studies are needed to determine whether changes in the
viral RNA polymerase play a role in virus transmission?
3. What studies are needed to define environmental factors that
contribute to virus transmission and how they interact with
genetic factors?
4. What studies can be done to provide measures to predict
intraspecies changes in virus transmission?
5. What studies are needed to identify what measures, if any, can
alter intraspecies virus transmission and what the effects of these
measures?
6. What studies are needed to determine whether transmission
changes can be used to predict pandemic risk?