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?