(TH) outbreak pattern

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Tuesday March 28, 2006 The Star

 

Outbreak pattern

 

In 2004, several dead open-bill storks in Thailand tested positive for

H5N1, triggering accusations against migratory birds. But the species

had migrated from Bangladesh and India – both free of the bird flu

then. Further scrutiny revealed that the birds had fed in fields

within one of Thailand's worst-hit bird flu region. Hence, the storks

were not the source of the virus but the victims.

 

The wild birds-are-to-blame theory gathered momentum when some 6,000

wild birds, mostly bar-headed geese but also gulls, shelducks and

cormorants, died of the virus in Qinghai Lake, north-west China in

2005.

 

Wild bird deaths were subsequently reported from Kazakhstan, Lake

Erhel in Mongolia, Romania and Croatia. The virus genotypes found in

these countries were almost identical to those of dead birds at

Qinghai Lake. This further fuelled the wild bird theory.

 

However, BirdLife International communications manager Dr Richard

Thomas disputes claims that the geese from China had spread the virus

to Europe. " No species migrates west from Qinghai to Eastern Europe.

When plotted, the pattern of outbreaks follows major road and rail

routes, not flyways. "

 

Investigation found the strain in the geese to be linked to a poultry

outbreak in southern China. Furthermore, the wild bird deaths in

Qinghai and those in Lake Erhel occurred outside of migration time. So

poultry infection cannot be ruled out.

 

Three types of wild bird species have been involved in outbreaks so

far. They are the scavenging species (crows and magpies), species that

often feed and scavenge in waterways near towns and farms (herons,

egrets and gulls) and colonially-nesting or flocking waterfowl that

feed in water bodies or in nearby farmland.

 

Outbreaks of H5N1 avian influenza among wild birds:

 

Japan and South Korea (March 2004): Crows and magpies found dead close

to poultry outbreaks.

 

Hong Kong (2004 and 2005): Peregrine falcon and grey heron, associated

with deaths of semi-captive birds in a park and poultry outbreaks.

 

Cambodia (February 2004): Wild birds in a zoo collection.

 

Thailand (December 2004): Pigeons, open-bill storks, little cormorant,

red-collar dove, scaly-breasted munia and black drongo.

 

Lake Qinghai, China (May/July 2005): 6,000 birds, mainly bar-headed

geese but also great black-headed gulls, brown-headed gulls, ruddy

shelducks and great cormorants.

 

Siberia and Kazakhstan (July/August and November 2005): A few wild

birds, associated with poultry outbreaks along major transport routes.

 

Lake Erhel, Mongolia (August 2005): 80 bar-headed geese and whooper swans.

 

Romania (October 2005): Two swans, two geese and one heron. Poultry

outbreak at the same time.

 

Croatia (October 2005): 30 swans (out of a population of 1,744) at

fish ponds. Tests on 2,000 wild and domestic birds, including ducks,

coots and cormorants on the same fish ponds, were negative for H5N1.

 

Malaysia (March 2006): One cattle egret

 

Sources: Birdlife International, Food and Agriculture Organisatio