Monday, March 24, 2008

Mallard Ducks Found To Be Asymptomatic To Bird Flu Virus



# 1818



On Saturday I wrote a blog I called Reservoir Ducks, where I suggested that ducks may be the ideal host to spread the H5N1 bird flu virus because, quite often, they appear immune to its ill effects. 



By coincidence, late yesterday an article appeared in next month's Emerging Infectious Disease Journal which expands on this very idea.  Researchers infected a number of species of ducks to see which ones shed the most virus and remained asymptomatic.



Mallard ducks, it seems, are big shedders of the virus but suffer little in the way of ill effects, making them an ideal carrier of the bird flu virus.


This report from Jason Gale of Bloomberg.




Bird Flu Scientists Say Mallards May Carry Virus Long Distances

By Jason Gale

March 24 (Bloomberg) -- Scientists in the Netherlands tracking the spread of bird flu in wild ducks say mallards may be the best long-distance carrier of the deadly H5N1 virus.


Researchers at the Erasmus Medical Center in Rotterdam experimentally infected six wild-duck species with H5N1 to determine which were capable of excreting the virus without succumbing to the disease. Pochards and tufted ducks shed the most virus, though tend to become ill or die earlier, they said.


``Of the six wild duck species studied, the mallard is the prime candidate for being a long distance vector,'' the researchers wrote in a study published in the April edition of Emerging Infectious Diseases.


``It was the only species to show abundant virus excretion without clinical or pathologic evidence of debilitating disease.''



The study suggests mallards should be given priority in any surveillance for the H5N1 virus in wild ducks, the authors wrote. The H5N1 strain has spread to more than 60 countries since 2003 through trade in poultry and the movement of wild birds. It has infected people in 14 countries and world health officials say it may spark a pandemic if it becomes capable of spreading among humans through coughing and sneezing.




The actual research paper can be found here:



Wild Ducks as Long-Distance Vectors of Highly Pathogenic Avian Influenza Virus (H5N1)

Juthatip Keawcharoen,* Debby van Riel,* Geert van Amerongen,* Theo Bestebroer,* Walter E. Beyer,* Rob van Lavieren,* Albert D.M.E. Osterhaus,* Ron A.M. Fouchier,* and Thijs Kuiken*



Wild birds have been implicated in the expansion of highly pathogenic avian influenza virus (H5N1) outbreaks across Asia, the Middle East, Europe, and Africa (in addition to traditional transmission by infected poultry, contaminated equipment, and people).


 Such a role would require wild birds to excrete virus in the absence of debilitating disease. By experimentally infecting wild ducks, we found that tufted ducks, Eurasian pochards, and mallards excreted significantly more virus than common teals, Eurasian wigeons, and gadwalls; yet only tufted ducks and, to a lesser degree, pochards became ill or died.


These findings suggest that some wild duck species, particularly mallards, can potentially be long-distance vectors of highly pathogenic avian influenza virus (H5N1) and that others, particularly tufted ducks, are more likely to act as sentinels.

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