RE: Avian flu - Good news for North America?

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The Reader's Digest version - there is a very low incidence of transmission of

viruses by birds through the Aleutian - Barent's Sea passageway.

AVIAN INFLUENZA, POULTRY VS MIGRATORY BIRDS (14)

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A ProMED-mail post

<http://www.promedmail.org>

ProMED-mail is a program of the

International Society for Infectious Diseases

<http://www.isid.org>

Date: Tue 13 Mar 2007

Source: EID, Volume 13, Number 4; April 2007 [edited]

<http://www.cdc.gov/eid/content/13/4/06-1072.htm>

" Movements of birds and avian influenza from Asia into Alaska. "

Winkler et. al.

Abstract:

Asian-origin avian influenza (AI) viruses are spread in part by

migratory birds. In Alaska, diverse avian hosts from Asia and the

Americas overlap in a region of intercontinental avifaunal mixing.

This region is hypothesized to be a zone of Asia-to-America virus

transfer because birds there can mingle in waters contaminated by

wild-bird-origin AI viruses. Our 7 years of AI virus surveillance

among waterfowl and shorebirds in this region (1998-2004; 8254

samples) showed remarkably low infection rates (0.06 percent) [There

were only 5 positive samples, and none were H5. - Mod.MHJ]. Our

findings suggest an Arctic effect on viral ecology caused perhaps by

low ecosystem productivity and low host densities relative to

available water. Combined with a synthesis of avian diversity and

abundance, intercontinental host movements, and genetic analyses, our

results suggest that the risk and probably the frequency of

intercontinental virus transfer in this region are relatively low.

Discussion:

Our surveillance did not show a " hotspot " of AI virus infection among

avian hosts. Much higher infection rates are known from other

multiyear surveillance studies at lower latitudes, e.g., Delaware Bay

(4.7 percent, [32]), southern Minnesota (10.8 percent, [5]), and

Alberta (22.2 percent, [32]) and British Columbia in Canada (55

percent, although only a single-year study, [33]). The infection

rates we found are substantially lower than those found for interior

Alaska (9 percent, [12]). Arctic conditions in Alaska prevail well

south of the Arctic Circle in the treeless regions of western Alaska,

and the US Arctic includes the Alaska Peninsula and Aleutian

Archipelago (34), a tundra ecosystem where our sampling was

concentrated (for Figure go to source). Aerial surveys of waterfowl

across Alaska show more ponds and fewer ducks per unit area on

tundra; the number of ducks per pond on tundra habitat (2.1) is less

than half the number found in the boreal-forest dominated interior

(5.5, [18]). This simple ecologic factor (perhaps due to the lower

productivity of these tundra ecosystems), resulting in the dilution

of virus in waters with fewer available hosts, may in part explain

our results. This is the 1st geographically and taxonomically

extensive Arctic AI surveillance in North America, and it suggests

that some Arctic effect lowers infection rates, thus lowering the

risk of intercontinental viral transfer in these high-latitude

regions. Our infection rates are low, comparable to those occurring

at much lower latitudes (e.g., 9,35), whereas mid-latitude rates can

be 2-3 orders of magnitude higher (33).

Human population densities in Alaska are relatively low, especially

in the Beringian Crucible, and Alaska lacks a large agricultural

sector. However, mammalian carnivores abound and could be susceptible

hosts (36). Direct human infection from wild birds is possible, but

transmission from birds to humans is difficult (37,38). Nevertheless,

exposure in this region may be considerable; hunters kill around 99

000 waterbirds for food each year on the Yukon-Kuskokwim Delta alone (39).

Although the existence of North American and Eurasian viral lineages

is well established in the literature, evidence from other regions of

North America has shown that geographic structure has been

insufficient to prevent sporadic intercontinental exchange of some

hemagglutinin subtypes (29,40). Our results can be considered to

confirm the comparative rarity of such events in this important

region of Alaska. Despite high diversity of host species and high

numbers of individual birds in Alaska making intercontinental

movements, the low AI infection rates and the genetic attributes of

virus isolates (29) suggest that at most only small numbers of

Asian-origin AI viruses or genes likely arrive in Alaska annually.

Although AI viruses from Alaska have a clear link with other viruses

in the lower 48 US states (29), the predominance of Arctic ecologic

conditions and the lack of agriculture in the Alaska region most

affected suggest a low risk for intercontinental viral transfer in this region.

References

5: Hanson BA, Stallknecht DE, Swayne DE, LA, Senne DE. Avian

influenza viruses in Minnesota ducks during 1998-2000. Avian Dis.

2003;47:867-71.

9: Chen H, GJD, Li KS, Wang J, Fan XH, Rayner JM, et al.

Establishment of multiple sublineages of H5N1 influenza virus in

Asia: implications for pandemic control. Proc Natl Acad Sci U S A.

2006;103:2845-50

12: Ito T, Okazaki K, Kawaoka Y, Takada A, Webster RG, Kida H.

Perpetuation of influenza A viruses in Alaska waterfowl reservoirs.

Arch Virol. 1995;140:1163-72.

18: Conant B, Groves DJ. Alaska-Yukon waterfowl breeding population

survey [report]. Juneau (AK): US Fish and Wildlife Service; 2005.

29: Spackman E, Stallnecht DE, Slemons RD, Winker K, Suarez DL,

M, et al. Phylogenetic analyses of type A influenza genes in natural

reservoir species in North America reveals genetic variation. Virus

Res. 2005;114:89-100.

32: Krauss S, D, Pryor SP, Niles L, Chenghong L, Hinshaw VS,

et al. Influenza A viruses of migrating wild aquatic birds in North

America. Vector-Borne Zoonotic Dis. 2004;4:177-89.

33: Canadian ative Wildlife Health Centre. Avian influenza

reports. 2006 [cited 12 Apr 2006]. Available from

<http://wildlife1.usask.ca/en/aiv/duck_survey_region.php>.

35: Stallknecht DE, Shane SM, Swank PJ, Senne DA, Kearney MT. Avian

influenza viruses from migratory and resident ducks of coastal

Louisiana. Avian Dis. 1990;34:398-405.

36: Thanawongnuwech R, Amonsin A, Tantilertcharoen R,

Damrongwatanapokin S, Theamboonlers A, Payungporn S, et al. Probable

tiger-to-tiger transmission of avian influenza H5N1. Emerg Infect

Dis. 2005;11:699-701.

37: Beare AS, Webster RG. Replication of avian influenza viruses in

humans. Arch Virol. 1991;119:37-42.

38: Shinya K, Ebina M, Yamada S, Ono M, Kasai N, Kawaoka Y. Avian

flu: influenza virus receptors in the human airway. Nature. 2006;440:435-6.

39: Wentworth C. Subsistence harvest survey Yukon-Kuskokwim Delta,

1995-2000 [report]. Anchorage (AK): US Fish and Wildlife Service; 2004.

40: Makarova NV, Kaverin NV, Krauss S, Senne D, Webster RG.

Transmission of Eurasian avian H2 influenza virus to shorebirds in

North America. J Gen Virol. 1999;80:3167-71.

- --

ProMED-mail

[One should never say " never " , but the authors' comment that " the

risk and probably the frequency of intercontinental virus transfer in

this region are relatively low " would seem to be cautiously on the

high side, that is, the risk is probably negligible. - Mod.MHJ, JW]

" A prudent man foresees the difficulties ahead and prepares for them; the

simpleton goes blindly on and suffers the consequences. " Proverbs 22:3

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[Guest guest]

My goof - I meant to say Bering's Sea

Larry wrote: The Reader's Digest version

- there is a very low incidence of transmission of viruses by birds through the

Aleutian - Barent's Sea passageway.

.

" A prudent man foresees the difficulties ahead and prepares for them; the

simpleton goes blindly on and suffers the consequences. " Proverbs 22:3

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