Laidback Al
Well-known member
Will ducks be the source of an H5N1 pandemic?
Most confirmed human H5N1 cases have been attributed to cross species transmission from sick or died chickens (e.g. the most recent case in Indonesia, an 8 year old girl that died). However, infections from domestic ducks seem to present a more serious pandemic threat based new lines of evidence.
In 2009, Jeong-Ki Kim and colleagues published an article entitled “Ducks: The “Trojan Horses” of H5N1 influenza” (full article). The authors speculate that wild ducks, as the main reservoir of HPAI, could be “silent spreaders” of H5N1 and could easily make a transmission leap to other species including humans.
They state in part
Shifts in receptor binding
The authors of the article cited above suggest that a shift in receptor binding has been taking place in wild and possibly domestic ducks. A PHD dissertation from 2010 seems to confirm that ducks are more likely to transmit H5N1 through there respiratory system rather than through their excrement (FT link).
The shift of receptor binding from lower to upper airways for H5N1 poses an increased risk for airborne transmission as demonstrated by Fouchier’s recent H5N1 transmission study. So, asymptomatic ducks shedding the H5N1 virus from the oropharynx should be a concern.
Fouchier notes that the laboratory created, aerosolized H5N1 virus
Asymptomatic ducks
Confirming that ducks can be asymptomatic carriers of H5N1 is a 2012 article noting that clinically healthy ducks in Indonesia are carrying H5 antibodies (link). Similarly, another study from Vietnam published in 2012 shows that about 3.3% of the pooled samples from live ducks tested positive for H5N1 with up 6% of the ducks from Mekong delta testing positive (FT link).
Increases in H5N1 infections in ducks
Since the beginning of 2012 numerous confirmed and suspected outbreaks of H5N1 among ducks have been reported in Vietnam, China, and elsewhere. Whether these outbreaks represent an uptick in H5N1 infections in ducks is not clear.
Vietnam - Nghe An province, 1,300 ducks destroyed following H5N1 positive test Jan 2012
Indonesia: Hundreds of ducks die in Lumajang, E. Java-poisoning suspected Jan 2012
South Korea starts investigation mass bird deaths - no H5N1 found Jan 2012
India - Bird flu resurfaces in Tripura 6.2k birds culled Jan 2012
Vietnam - Haiphong: discovered new outbreak of influenza A H5N1 in ducks Feb 2012
H5N1-infected poultry appeared in Quang Tri Feb 2012
Vietnam Ha Tinh: outbreak of avian influenza H5N1 Feb 2012
Vietnam: Quang Nam renewed outbreak of avian flu in ducks Feb 2012
China - 1000s ducks dead - suspected cholera or H5N1 bird flu in Zhuzhou, Hunan province Feb 2012
Vietnam - Detection of influenza A/H5N1 virus in ducks in Hanoi Mar 2012
Ducks infected with influenza A/H5N1 in Quang Ngai Mar 2012
China - H5N1 bird flu outbreak reported in ducks, 17,127 culled in Xinhui district, Jingmen, Guangdong province June 2012
But what is clear is that H5N1 infected ducks pose a pandemic threat. A recent article reviewed potential risk factors for H5N1 (abstract link). Although the authors do not apparently single out ducks, they identified domestic waterfowl and the presence of a water source as two of the main statistical associations with HPAI H5N1 outbreaks across all regions studied.
Recent Human Case in China
Perhaps the most evident example of the potential for H5N1 infections from ducks is the 2 year old child in Guangdong Province in China. The child most likely contracted the virus from an infected, but asymptomatic, duck that was slaughtered in a local wet market in the Haizhu District. The child was apparently present when the duck was slaughtered (FT link).
Conclusion
All of this information taken together suggests that ducks pose a special risk for harboring and transmitting H5N1. Not only are asymptomatic domesticated ducks a vector for H5N1 transmission but they could also be the mixing vessel for an aerosolized strain transmissible among humans. There needs to be increased surveillance in both wild and domestic duck populations for H5N1 with a particular emphasis on wet markets. It now seems that an H5N1 pandemic strain could make the jump to humans from diseased ducks just as likely as from infected chickens.
Most confirmed human H5N1 cases have been attributed to cross species transmission from sick or died chickens (e.g. the most recent case in Indonesia, an 8 year old girl that died). However, infections from domestic ducks seem to present a more serious pandemic threat based new lines of evidence.
In 2009, Jeong-Ki Kim and colleagues published an article entitled “Ducks: The “Trojan Horses” of H5N1 influenza” (full article). The authors speculate that wild ducks, as the main reservoir of HPAI, could be “silent spreaders” of H5N1 and could easily make a transmission leap to other species including humans.
They state in part
Shifts in receptor binding
The authors of the article cited above suggest that a shift in receptor binding has been taking place in wild and possibly domestic ducks. A PHD dissertation from 2010 seems to confirm that ducks are more likely to transmit H5N1 through there respiratory system rather than through their excrement (FT link).
The shift of receptor binding from lower to upper airways for H5N1 poses an increased risk for airborne transmission as demonstrated by Fouchier’s recent H5N1 transmission study. So, asymptomatic ducks shedding the H5N1 virus from the oropharynx should be a concern.
Fouchier notes that the laboratory created, aerosolized H5N1 virus
Asymptomatic ducks
Confirming that ducks can be asymptomatic carriers of H5N1 is a 2012 article noting that clinically healthy ducks in Indonesia are carrying H5 antibodies (link). Similarly, another study from Vietnam published in 2012 shows that about 3.3% of the pooled samples from live ducks tested positive for H5N1 with up 6% of the ducks from Mekong delta testing positive (FT link).
Increases in H5N1 infections in ducks
Since the beginning of 2012 numerous confirmed and suspected outbreaks of H5N1 among ducks have been reported in Vietnam, China, and elsewhere. Whether these outbreaks represent an uptick in H5N1 infections in ducks is not clear.
Vietnam - Nghe An province, 1,300 ducks destroyed following H5N1 positive test Jan 2012
Indonesia: Hundreds of ducks die in Lumajang, E. Java-poisoning suspected Jan 2012
South Korea starts investigation mass bird deaths - no H5N1 found Jan 2012
India - Bird flu resurfaces in Tripura 6.2k birds culled Jan 2012
Vietnam - Haiphong: discovered new outbreak of influenza A H5N1 in ducks Feb 2012
H5N1-infected poultry appeared in Quang Tri Feb 2012
Vietnam Ha Tinh: outbreak of avian influenza H5N1 Feb 2012
Vietnam: Quang Nam renewed outbreak of avian flu in ducks Feb 2012
China - 1000s ducks dead - suspected cholera or H5N1 bird flu in Zhuzhou, Hunan province Feb 2012
Vietnam - Detection of influenza A/H5N1 virus in ducks in Hanoi Mar 2012
Ducks infected with influenza A/H5N1 in Quang Ngai Mar 2012
China - H5N1 bird flu outbreak reported in ducks, 17,127 culled in Xinhui district, Jingmen, Guangdong province June 2012
But what is clear is that H5N1 infected ducks pose a pandemic threat. A recent article reviewed potential risk factors for H5N1 (abstract link). Although the authors do not apparently single out ducks, they identified domestic waterfowl and the presence of a water source as two of the main statistical associations with HPAI H5N1 outbreaks across all regions studied.
Recent Human Case in China
Perhaps the most evident example of the potential for H5N1 infections from ducks is the 2 year old child in Guangdong Province in China. The child most likely contracted the virus from an infected, but asymptomatic, duck that was slaughtered in a local wet market in the Haizhu District. The child was apparently present when the duck was slaughtered (FT link).
Conclusion
All of this information taken together suggests that ducks pose a special risk for harboring and transmitting H5N1. Not only are asymptomatic domesticated ducks a vector for H5N1 transmission but they could also be the mixing vessel for an aerosolized strain transmissible among humans. There needs to be increased surveillance in both wild and domestic duck populations for H5N1 with a particular emphasis on wet markets. It now seems that an H5N1 pandemic strain could make the jump to humans from diseased ducks just as likely as from infected chickens.