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The Rice-Duck Connection: mechanism for HPAI H5N1 re-emergence?

by: SusanC

Fri Mar 09, 2007 at 00:02:35 AM EST


SusanC :: The Rice-Duck Connection: mechanism for HPAI H5N1 re-emergence?
Recently, HPAI H5N1 appeared again in Vietnam, after relatively successful efforts to eradicate it with culling and vaccinations.  Is this re-introduction from commercial activity or migratory birds, or had the virus never left, but had been hidden in a reservoir and is now re-emerging?  Current signs are while there might be some introduction due to trading, re-emergence is probably a bigger problem.  According to Robert Webster, the virus is found in domestic ducks which do not get sick, but become long-term shedders. More importantly, the virus is undergoing ongoing antigenic drift, with multiple variant strains being commonly found in one duck now.  Crucially, the HPAI virus has not been found in migratory birds in recent months.

The role of the domestic duck in perpetuating HPAI is now increasingly recognized.  The following maps from this paper Free-grazing Ducks and Highly Pathogenic Avian Influenza, Thailand, Gilbert et al, 2006 illustrate the correlation between HPAI outbreak and free-grazing domestic ducks.  Notice how both chicken and duck outbreaks correspond geographically to breeding of domestic ducks but not chickens. 

In addition, when compared to the production of rice crop, HPAI outbreak areas also correspond to areas producing 2 or more crops a year, while areas producing single crops did not experience any outbreaks.

What does that tell us?  Rice growing needs a lot of water, as the paddies need to be flooded for much of the crop cycle.  Fields that are only rainfed can only yield one crop a year, while irrigated plots can support 2 or more crops.  Now, if you are raising ducks, you can give them commercial feed, or you can turn the ducks out onto the fields, and they can feed naturally on the pests during the growing period and on the left-over grains after the harvest.  If you live in areas with year-round rice cultivation, it is possible to breed ducks entirely by `herding' them onto paddies and letting them graze there, hence the name `grazing ducks'.

Lest you imagine that ducks are just grazing at paddies down the road, in reality, the pressure for profit means that farmers often herd their ducks over long distances to graze at paddies.  Here is an example from Domestic Ducks and H5N1 Influenza Epidemic, Thailand Songserm et al, EID, 2006, showing how ducks are transported over long distances.

(Caption for above: Example of grazing-duck movement. A single flock of ducks was moved 3 times by truck in 1 season in 2004. The size of the flock is 3,000-10,000. The time spent at each site depends on the availability of rice fields at the site: an acre of rice could support 3,000 ducks for 1 to 2 days. The duck owners have agreements with the landowners regarding the time of harvest and the acreage available. One flock could spend as long as 1 month at a single site before being moved to the next.)

The above studies tell us that HPAI outbreaks are associated with the breeding of grazing ducks, and places with multiple rice crops per year are more likely to support these ducks than single crop areas.  The movement of ducks over long distances of course perpetuates the problem. 

What this means, interestingly, is that you can more-or-less predict where HPAI is more likely to occur by looking at charts of the distribution of double-crop areas.  There are now various technologies available to do satellite remote sensing of landscape to monitor the use of land, including in particular the presence of rice paddies.  Here is an interesting study Combining remote sensing and ground census data to develop new maps of the distribution of rice agriculture in China, Frolking  et al, Global Biogeochemical Cycles, 2002.

Which brings us to the question of the emergence of HPAI H5N1 in southern China in the past decade, which I've been wondering about for a long time.  The question that I had was why southern China?  This may be giving us a clue.  In addition, look at the following chart showing the tremendous growth of duck meat production in China.

(From Avian influenza, domestic ducks and rice agriculture in Thailand Gilbert et al, Agriculture, Ecosystems and Environment 119 (2007) 409-415)

What about other countries?  Webster says that the HPAI virus is now endemic in domestic ducks in Indonesia, China, Vietnam, Egypt, Nigeria.  Which brings me to a point made by Okieman in this diary The Rice - H5N1 Connection, where he posted several links showing how countries HPAI outbreaks are all major rice producers.  In addition, in Egypt both avian and human outbreaks are concentrated along the Nile, which comprises of flooded lowlands (which, btw, was also found to be correlated to outbreaks in Thailand, as opposed to higher altitudes) suitable for rice production.  Indeed, the major rice producing region of Egypt is concentrated at the Nile delta, which is where we are seeing most of the human cases. 

This same pattern is also seen in Indonesia.  This map is from Mapping paddy rice agriculture in South and Southeast Asia using multi-temporal MODIS images Xiao et al, Remote Sensing of Environment 100 (2006) 95 - 113.

The text of this paper says "While each of Indonesia's five main islands has some areas of intense rice production, heavily populated Java is the most productive rice area".

Finally, I come to a specific problem with this system of raising ducks on paddy fields.  For the past decade, this system has been actively advocated as part of sustainable agriculture.  Called rice-duck, the idea is to encourage and teach farmers to breed ducks on their paddies in order for pest control, which reduces the use of chemicals, increase rice yield, while of course bringing extra income and protein in the form of ducks and eggs. 

This is part of the Global Integrated Production and Pest Management (IPPM) development program by the FAO.  Check out this The Duck Ranger: Rice-Duck Systems to the Rescue, a World Bank report, which includes a comment that the leader of this project to teach rice-duck farming in the Philippines was one of the winners of the World Bank's Young Scientist Award 2005.

One question that has been asked numerous times is why is there no HPAI in the Philippines?  It could be that they are just lucky, or they did not import the same poultry stock as Indonesia.  However, the fact that the World Bank has a program in the Philippines to teach rice-duck integrated farming tells me that the method is probably not indigenous there.  Not being able to find any information, I asked a Philippino friend who, as soon as I mentioned ducks, said "But you can't keep ducks on paddies cos they will walk on the crop and ruin it."  Interestingly, I found from this document Rice-duck farming: new opportunities for farmers in Bangladesh that Bangladeshi farmers have similar beliefs "Most farmers farm rice and ducks separately, fearing that ducks would harm their rice crops."

To conclude, there are reasons to suggest that the following specific agricultural practices in combination may be contributing to the endemicity, re-emergence, and spread of HPAI H5N1:
  1. Multiple rice crops per year
  2. breeding of free-grazing ducks on paddies
  3. large flock size
  4. movement of flocks over long distances

Whether we can find solutions or alternatives to these practices, I would suggest that at least in countries where rice-duck is not indigenous practice, that development programs promoting such practice should probably be halted pending further research.

UPDATE Mar 17

This is a composite chart made from FAO maps for vietnam showing (from left to right)
1st row: HPAI outbreaks 2003-04, HPAI outbreaks 2004, chicken density, poverty density, share of rural household raising poultry
2nd row: Mean poultry holding area, raw poultry density, share of commune area irrigated paddy, accessibility, chicken to duck/goose ratio.

Notice which of the various maps correspond to the HPAI outbreaks.

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Lots to digest.
The challenges, if this is true, are very significant. 

Start with inadquate compensation for flocks taken to protect against spread of H5N1.  Add suggested reduction of rice crops.

Stir well and add heat.  Wait a surprisingly short time and presto.

"Societal Disruption" followed by new government.

I am always skeptical of this kind of analysis when the ax being ground could be owned by those whose profits are reduced by the more natural farming technique, but if Webster (St Jude Childrens - top expert) is putting his credibility in play by raising this as a possiblity for further study (which I gather is all we are getting here) in my mind it is worth a staight look.

ITW(Joel J)
Courage is resistance to fear, mastery of fear - not absence of fear.
- Mark Twain
 


this is from multiple sources
Webster is not raising this directly, not in full anyhow, only that the domestic duck is the reservoir and that they are being moved over long distances.  The rest is from the work of Gilbert on spatial epidemiology in Thailand and Xiao et al on remote sensing.  I put all that together with the context of sustainable development programs and rice producing countries, etc.  The hypothesis about the Philippines is entirely my own guessing.  ;-)



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
Gotta admire the smarts. Glad you haven't turned your genius to nefarious ends. :^} nt


ITW(Joel J)
Courage is resistance to fear, mastery of fear - not absence of fear.
- Mark Twain
 


[ Parent ]
ducks and rice...
I understand the connection, and it does make a lot of sense for many of the outbreaks.  But I still have questions.

How can this duck/rice theory be applied to landlocked areas such as Hungary, and various semi-arid areas of Africa and the middle east? 


this is about persistence
re-emergence, and endemicity.  I'm not sure that outbreaks in Hungary indicate any endemicity.

Africa and the middle East: Egypt certainly fulfills the pattern.  Nigeria is the biggest rice producer in Africa.  I haven't looked up its topography, partly because I'm not sure that we are getting accurate reporting of where outbreaks are occurring.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
we need people to look into safer practices, too!
I.e., one problem here is that ducks are moved around, right?  So, why are so many ducks kept together?  Couldn't there be smaller flocks that wouldn't have to move around, or at least not so far away?

In short: What are the alternatives?  What's the least-resistance alternative?  Is there an alternative that makes sense from both an economical and epidemiological point of view?  How do we/others get the ball rolling in a more apropriate direction?

Same was said about pigs eating chicken waste.  Folks could use biodigesters (here, too) to get both biogas (good stuff for peakoil, no?) and compost for their crops, and feed pigs on crops (provided crops are not better and they can raise less pigs altogether).

You arm yourself to the teeth just in case.  You don't leave the gun near the baby's hand.


The ducks are moved up to 100 km across country to market.
This is beneficial for the rice farmer as well as for the duck farmer.  The ducks are allowed free passage through the rice fields, where they eat fallen rice (free food for the flock).  The rice farmer benefits as the ducks fertilize his field. 

It's always been a very mutually beneficial arrangement for everyone.


[ Parent ]
several things
they are not moved 100km just to market, but to feed on various fields.

Secondly, no it's not always beneficial.  Not if they create the conditions for HPAI. 

Third, such huge no of birds freely feeding on fields means that once infected, they leave their droppings on the field, and the continuing crop growing never allows the soil to dry out.  Other ducks come along and pick up the virus.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
yes, that's why I said it "has" always been
a mutually beneficial relationship between the farmers moving their ducks to market and the rice farmers.

This is a traditional relationship, a practice of longstanding.

In the past, it worked out well for everyone.  Now, there are new risks.  It's very hard to change these traditional practices, but it will have to be done. 


[ Parent ]
yes, now there are new risks
What was sustainable in traditional practice becomes unsustainable when you try to turn that into commercial scale.  Think, for example, how couple of hundred years ago, you wouldn't be able to 'herd' your flock for longer distances than you can walk!  And you probably can't handle a 5000 duck flock either, nor have ways of selling them quickly when they all mature at the same time.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
Great work Susan (as always)
When Okieman brought this up before I thought at least intuitively it all made sense and your maps help solidify it.  It's interesting that certain cultures think differently about ducks vs others.  But have we seen cases of duck farmers infected?(or thier children since so many young people are effected).  I thought in cases where there was a likely B2H link it appeared to be chicken-human.  So then the other question is how does it get from ducks to chickens?  Do duck farmers raise both?  Do they bring the ducks home sometimes and let them mingle with chickens?  Or is the answer that this thing has spread to so many other species (cats, mice, birds, who knows what else) that we are getting multiple infection sources, perhaps even varying by country depending on farming practices?  I wonder if the sequences by country might coincide with this? 

duck farmers
It could be that some of them have so much exposure to various avian viruses that they have varying degrees of cross immunity to the virus, I don't know.

The route of transmission is more often duck to chicken, sometimes duck to human.  The ducks are rounded up at night and kept in very packed conditions often with the chicken flock, and that is where cross-infection can take place.

About other species: I don't think we need the existence of other species to explain re-emergence, as a continuing circulation of the virus among the ducks would create the conditions for that, although the presence of intermittent transfer to mammalian hosts back to avian might cause selection of mammalian adaptation.

Plus the addition of poultry vaccines that are not really suitable for ducks ie partially effective vaccination would probably enhance the state of chronic virus shedding, which is what creates the huge amount of exposure to variants that the ducks are getting from each other.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
I'll have to echo kelly phan's
comment. It still leaves some unanswered questions that are at the heart of this problem.

How is this disease being spread to other countries that have nothing to do with the production of rice, such as russia, europe, kwait, Iran, Iraq? (unless these countries produce rice and use ducks that I am unaware of.)

And in these countries, what is the duck ratio to chickens?

And are the areas on infections in the Indo/Asian countries
more on the duck ratio or chicken ratio? We do not hear of major duck culling like we hear of major chicken culling. Reports from confirmed cases in Indonesia, say that the families had chickens, but not ducks. How are the chickens becoming infected if ducks are not generally around the chickens. I'm sure that are cases where chickens are not exposed to ducks.

Overall, well written SusanC. It does, for the most part make a great deal of sense.

United we stand: Divided we fall
www.flunewsnetwork.com


[ Parent ]
Ducks usually don't look sick.
So the problem is hidden. However, there was at least one case last year in China where about half a million ducks were culled.

The main point of this diary is persistent reemergence of outbreaks in some countries. Other countries you listed may have infection by migratory birds or commercial activity.

You want perspective. I want perspective. Let's talk. We don't have to agree on every thing. If we do, one of us is redundant.


[ Parent ]
I understand the main point of the diary
However, one cannot discuss this topic, without discussing the other. they are to interconnected. If that is the source of H5N1, that was then. This is now, and it has spread like a raging fire, and we need to find out how this is spreading. half a million ducks being culled is nothing conpared to the number of chickens that's been culled over the years in countries. I think that number far exceeds half a million. It seems to me, just MHO, that the tables have turned, and it's now the chickens that has become the target because of infection rates. Ducks may carry this, but it is the chickens that's making people sick and causing them to die.

United we stand: Divided we fall
www.flunewsnetwork.com


[ Parent ]
Thanks.
It still leaves some unanswered questions that are at the heart of this problem.

Of course, ;-) I don't imagine that this explains everything.  I only picked out one particular aspect, the issue of persistence.  This is not about spread, but re-emergence in specific countries that seem to get the virus again and again.

How is this disease being spread to other countries that have nothing to do with the production of rice, such as russia, europe, kwait, Iran, Iraq?

Spread is a different story, it can be partly due to trade, partly due to migratory spread.  It is interesting that this season they didn't find any more HPAI in wild birds.  Could it be that the virus has drifted and therefore is no longer carried by wild species over long distances?  Could it be that wild birds are no longer infected this season?  I don't know the answer to that.

I don't know about duck to chicken ratio, and I'm not sure I understand why that is important?  But ducks that are asymptomatic would not be culled, that's part of the problem.

The ducks are around the chickens.  They are rounded up either every night or whenever they need to be brought in or moved, and would very often be kept in very crowded conditions with the chickens.  If you look at the chart showing the growth in duck meat production in China, the growth in chicken is just as or ever more fast.  It's about the density of the flocks.

Think of a pandemic in humans, where you would have a lot more transmission in more densely populated areas.  More transmission also means more chance for antigenic drift.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
Ducks that are asymptomatic
would not show as postive upon testing, is that correct?

United we stand: Divided we fall
www.flunewsnetwork.com


[ Parent ]
no, they would show as positive
they just don't get sick, so you wouldn't know unless you test them.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
Is the behaviour of birds at different seasons significant?
With spring in the air (already!) I've noticed the ducks splitting up into smaller groups 2s n 3s. Do wild ducks meet up with domesticated birds more in the winter when there isn't sex and babies on the agenda?

[ Parent ]
Japan Rice-Duck Farming Society
http://carrot.memene...

Invented in Japan?

http://web-japan.org...

Furuno, the pioneer of the aigamo method of growing rice, has visited Cambodia, China, Indonesia, Malaysia, the Philippines, South Korea, Taiwan, and Vietnam in an effort to introduce the method.


You want perspective. I want perspective. Let's talk. We don't have to agree on every thing. If we do, one of us is redundant.


What happens if you domesticate wild ducks and raise them in rice paddies.
http://web-japan.org...

I can't believe what I read.


The aigamo is a cross between the kamo (wild duck) and the ahiru (domestic duck). Because kamo are migratory, it was believed that using ahiru would be better for agriculture. According to some experts, though, aigamo have come to be used because they produce a large amount of tasty meat and are easier to obtain than ahiru.


You want perspective. I want perspective. Let's talk. We don't have to agree on every thing. If we do, one of us is redundant.


[ Parent ]
10,000 families in Japan do this.
http://www.farmingso...

An integrated rice-duck cultivation method developed in Japan offers another approach to integrating duck-rice production.

[snip]


This method of chemical-free rice cultivation has aroused much interest in Japan, where some 10,000 families have adopted the system, and in Korea, China and Taiwan. Recently, Tanzania also began experimented with this organic alternative.

Notice this article was about duck raising in Vietnam.

You want perspective. I want perspective. Let's talk. We don't have to agree on every thing. If we do, one of us is redundant.


[ Parent ]
but if they don't do
intensive rice cropping, it might not be a problem.  If the fields have periods where they are just lying fallow and drained, and ducks are not on them, the virus might get a chance to die out. 



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
Chinese Ecological Agriculture, Greening The Desert, etc
http://www.scj.go.jp...

http://youtube.com/w... or http://www.permacult... "greening the desert"

Sometimes the question seems to be "What are we waiting for?"

You arm yourself to the teeth just in case.  You don't leave the gun near the baby's hand.


[ Parent ]
yes Furuno is the 'guru'
of rice-duck farming.

There is an International Rice-Duck Society promoting this as well.

Notice that countries that practice rice-duck integrated farming also include Japan and South Korea, where we see recurrent HPAI outbreaks even though these are advanced economies with high biosecurity.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
Stopping the Practice Seems Near Impossible
If the practice is as widespread as you describe and is part of the input for both rice production and duck production, the possibility of stopping it seems really remote.  (How do you replace the food supply and income lost?  Without that implementation of any plan seems as they say 'frought with difficulty'.)

Is there another way to break that chain, vaccination of the flocks, or somehow cleansing the water without harming the crops? 

I am not sure the remedy for this can be 'just say no', so what else is there?

ITW(Joel J)
Courage is resistance to fear, mastery of fear - not absence of fear.
- Mark Twain
 


Vietnam resumes practice
http://www.newfluwik...

You want perspective. I want perspective. Let's talk. We don't have to agree on every thing. If we do, one of us is redundant.

[ Parent ]
actually, seems like they might be doing something
cos it sasy "breeders can only raise the ducks and geese on closed farms".

This might be the way to go.  Not easy, but might make a difference.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
if the ducks are not freely grazing
but bred separately, it would mean a far lower production and higher cost, but it would reduce the extent of the problem.

I think it is simply the density of the flock and the intensity of farming that is the biggest problem, that if the virus load in the environment is less, the chance of continuous transmission is lower.

Remember each flock of duck gets sold ie gone after a few months, so the virus persists only because you are bringing in new flocks year round, into an environment where the fields never really get a break from this cycle of crop/pest/duck/harvest/duck/planting etc.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
how does this get to TPTB? hmmm - journalists out there?


You arm yourself to the teeth just in case.  You don't leave the gun near the baby's hand.

[ Parent ]
feel free to send a link
to anyone you want,  ;-)



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
Helen Branswell anyone? :-)


You arm yourself to the teeth just in case.  You don't leave the gun near the baby's hand.

[ Parent ]
simple, just vacsine the ducks...
instead of halting the practice, just make sure all ducks in this system is vacsineated. If it stops the virus form reapperaring all the time the money is vell spent, the numbers are much lover than the chicken numbers..

Such a substainable agriculture practice is of great importance.


[ Parent ]
duck vaccines don't work
Current poultry vaccines are designed for chickens not ducks.  They are being used in some places in China, but they don't really work.  The rate of seroconversion is even lower than for chickens, and they continue to shed the virus after vaccination.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
pitty..
I guess thats why we dont have seen a vacsine for pets yet either..
This slow progress of H5N1 vacsines are very special is it not?

But if it worked the ducks would not continue shredding virus would they? I thought a vacinated animal was like a dead end, a wall..


[ Parent ]
Excellent Article
Something is causing the reoccurance of BF in these rice producing countries (versus non-rice producing countries).  The double cropping system and rice duck grazing seems to be a common denominator.

One bit of testing I wish to see done is the mice/rats and insects (and their eggs) found in/nearby rice patties and harvested rice where bird flu has been found.  {H5N1 has been found to infect mice and rats, and influenza like viruses (Thogoto viruses) has been found to able to be incorporated in certain insects.}  It don't hurt to wish ;-)


I'm with you
on testing rats/mice.  I hope someone is working on it!



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
worldchanging on duck-rice
http://www.worldchan...

You arm yourself to the teeth just in case.  You don't leave the gun near the baby's hand.

read this
Furuno himself rotates the duck-rice system with vegetable crops, allowing him to maintain a highly productive operation on a small plot of land in Japan.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
If it weren't for H5N1 I'd say this is an amazing way to
utilize precious land, cut back on pesticdes, etc.  Only problem is....

[ Parent ]
I suspect it's not a problem
if you rotate the use of the land, and not have ducks in them year round.  See top diary about single crop vs multiple crops of rice a year/



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
link to worldchanging and growing rice and ducks
http://www.worldchan...

You arm yourself to the teeth just in case.  You don't leave the gun near the baby's hand.

oops, thought it was another diary! :-D


You arm yourself to the teeth just in case.  You don't leave the gun near the baby's hand.

[ Parent ]
It is the eggs
http://www.fao.org/d...

Pg 47 of pdf (Pg 36 of document) Egg Production 
"All interviewed farmers (150 respondents, 100%) mentioned that eggs is
their main purpose of duck farming. Duck becomes the output when they have
no production anymore and the duck were sold out as a culling duck."

Pg 59 of pdf (Pg 48 of document) Egg Collector (middleman)
"Marketing system of ducks output by majority respondents (78.7%) done
by a collector or middleman. Some farmers directly can make a contact because
have a connection with a middleman, other farmers sell egg through the group of
farmers who will continue to sell to a collector. Frequency of selling egg vary
from everyday to once in two weeks. Majority respondents shed egg to group of
farmers or directly to the collector/middleman everyday (52.7%). The collector
will collect eggs from farmer and then send it to markets. Several farmers sell
eggs directly to the customer around they live, the customer in the market or
send eggs to hatchery places. Nothing do to the egg collected by farmers from
the confinement before go to marketing cycles (Table 40)."

Comment:  Apparently the main use for ducks in Indonesia is not for their meat but for their eggs.  According to this report duck eggs are collected almost daily, sold to a collector (middleman), then shipped all over Indonesia.  If a flock is infected then the eggs (also infected) could be shipped into a neighboring province before anyone notices that some of the ducks appear sick.  They may even be asymptomatic, in which case they would not be noticed at all.  When the eggs were eaten the shells would be fed to the local chickens.  It appears to be very common for most folks to have a few chickens in the back yard.  Feeding egg shells to chickens is a very common practice here in Oklahoma and likely also in Indonesia, because it helps egg production.  The chickens in turn would become infected from the egg shells.  This mechanism could explain why there has been human H5N1 cases with no ill poultry in the neighborhood.  This could also explain why in a few cases the people became ill a few days before the local poultry did.

Which came first (and caused bird flu), the chicken or the (duck) egg?


I think that might contribute
but not as significantly, in terms of spread, as herding ducks over long distances.  We now know definitely that ducks shed viruses continuously, whereas we don't know how much contamination generally there is in eggs.

Secondly, that is only spread, it doesn't account for persistence from season to season and re-emergence.

I think the biggest factor is the environment of the paddies, ie being flooded almost year round, which does not allow the virus to die off.

Think of what they do now in wet markets in Hong Kong.  They have a 'rest day' each month, where all poultry stalls are closed, all birds taken away, and the whole place is disinfected and DRIED OUT, which they found was very effective in preventing recurrence. 



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
There can be at least enough virus
in eggs to detect, according to the attached article.  Would that not be enough to cause infection in humans?

http://www.foodconsu...


[ Parent ]
sorry, missed that from ages ago
Yes, but what you are saying is about transmission to humans.  

What this rice-duck issue deals with, is the repeated re-emergence of the virus in the flocks in places after apparent eradication has taken place.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
H5N1 virus in eggs
From the article linked below:

Transmission
Routes of bird-to-bird transmission include:
Airborne transmission if birds are in close proximity
Direct contact with contaminated respiratory secretions or fecal material
Vertical transmission is not known to occur
Other factors that contribute to spread within and between flocks include the following:
Broken contaminated eggs in incubators infecting healthy chicks (see References: OIE 2002)
Movement of infected birds between flocks

Movement of fomites such as contaminated equipment, egg flats, feed trucks, and clothing and shoes of employees and service crews (see References: APHIS: Highly pathogenic avian influenza; Beard 1998)
Contact with infected wild birds and waterfowl
Fecal contamination of drinking water
Garbage flies (suspected of transmitting the virus during the 1983-1984 epidemic in Pennsylvania) (see References: Beard 1998)
The disease is highly contagious. One gram of contaminated manure can contain enough HPAI virus to infect 1 million birds (see References: APHIS: Highly pathogenic avian influenza).

http://www.cidrap.um...

and

"Preliminary field and laboratory evidence indicates that virus can be recovered from the yolk and albumen of eggs laid by hens at the height of the disease."
http://www.upc-onlin...

Comment:  Apparently the virus could be transmitted to ducklings (or people)from the outside or inside of the eggs.  This could possibly also contribute to both the persistence and geographical distribution of the disease in ducks and humans.  To me, the most significant aspect of infected duck eggs being a source of infection is the ease of tranportation and distribution of eggs versus live animals.  Also, the lack of refrigeration would necessitate the timely harvest, transportation, sale and consumption of the eggs.

Of course none of this changes the importance of the relationship of double cropping of rice and the use of free range ducks in the persistence of the virus in rice patties.  It's just that the transportation of fertilized and unfertilized eggs may be another factor contributing to that persistence and the transmission of the virus to humans.

Finally, in the past there has been discussion concerning the transmission of influenza via flies.  I bolded the above text to point out to anyone interested that apparently it has occured before, at least between poultry.


[ Parent ]
Egg vendors on a train
Here is an excerpt from a blog describing one guys trip in Indonesia in December, 2005.  (An interesting read by the way.)  As has been noted more than once, many of the suspect cases have been from cities along railroad tracks. 

"We left Jakarta on the next available night train - boy was this a rough ride! The train was a piece of crap, and was a grueling 10 hour ride in a dirty dirty coach with more hawkers (street vendors) in the cabin than travelers. The whole night, non-stop, we were harassed by people selling duck eggs, inflatable pillows that have holes in them (thanks to whoever sold it to me), tofu, and all sorts of (in)edible items. These hawkers would sleep on top of trains or beside the track waiting for their next victims."

http://www.travelblo...


[ Parent ]
Coincidentally...
...here's a photo in an Arabic paper from today that's accompanying an AFP article about the latest, confirmed death in Indonesia (the woman from Riau) ... the caption reads [mach. trans.] Burning bad eggs in Indonesia

http://www.rmc-mo.co...

Proud FAF-er.


[ Parent ]
but all of these points ;-)
from everyone, are still about transmission, not about how come the virus keeps coming back in some places and not in others. 

For example, if hypothetically you stop all egg sales, would it stop the virus from coming back next season?  If the answer is no, then the reason for persistence lies somewhere else.

Of course transmission is a necessary condition for persistence and re-emergence, but it does not give us what is the critical component, which, if we can define it accurately, MIGHT give us a clue on how to approach eradication.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
Transmission equals persistence
My main reason for bringing up the duck egg issue was to address a potential mechanism in the transmission of the virus to people.  So much attention is being given to chickens and the culling thereof.  But a goodly amount of the transmission could be from duck eggs from asymptomatic free range ducks. If so, then local culling efforts in locations where the virus effects humans and poultry will just go so far.  The virus will continue to pop up time and again via the easy transportation of duck eggs.

Maybe I am barking up the wrong tree, but while looking for info concerning this issue I have found a huge amount of info concerning live ducks and their movement, but relatively little concerning eggs.  In Indonesia it appears the ducks are primarily raised for the eggs, not their meat.  According to Wikipedia adult Pekin ducks will lay an average of 200 eggs per year.  I know you have seen photos of the size of some of the flocks they raise.  That is alot of eggs being collected everyday and sold to the middlemen vendors.  Yes infected flocks of chickens and ducks need to be culled, but this will never stop the transmission and persistence of the disease as long as asymptomatic ducks keep laying infected eggs which keep getting transported from one end of Java to the next, or possibly to other countries.  I believe eggs need to be given a bit more attention primarily concerning the transmission of the disease to people, but I suspect it is also a factor in the continued transmission between flocks of both ducks and chickens.


[ Parent ]
you may be right on transmission
But a goodly amount of the transmission could be from duck eggs from asymptomatic free range ducks

but the question is what is the biggest obstacle for eradication?  If you consider the amount of duck poop (yes, that'a s technical word!) in the paddies which never dries out, then the environmental viral load is so high and persistent that whatever else you do is not going to change the situation.

That's why I mentioned the lesson from Hong Kong markets.  It's not enough to just stop transmission, you have to clean out the environment.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
Let me hightlight this point LOL
It's not enough to just stop transmission, you have to clean out the environment.

Which, a year after this diary was first written, is precisely the problem we are facing in various countries but particularly Indonesia.  They just never got the environment cleaned out, but keep bringing flock after flock to the fields.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
UPDATE: the FAO appears to agree with my hypothesis ;-D
Ducks and rice play key role in avian influenza outbreaks

New scientific findings published

26 March 2008, Rome - Ducks, people and rice paddies - rather than chickens - are the major factors behind outbreaks of H5N1 highly pathogenic avian influenza in Thailand and Viet Nam, and are probably behind outbreak persistence in other countries of the region such as Cambodia and Lao PDR.

In "Mapping H5N1 highly pathogenic avian influenza risk in Southeast Asia: ducks, rice and people", just published in the latest issue of the Proceedings of the National Academy of Sciences of the United States (PNAS), a group of experts from FAO and associated research centres looked at the series of waves of H5N1 highly pathogenic avian influenza (HPAI) in Thailand and Viet Nam between early 2004 and late 2005.

Initiated and coordinated by FAO senior veterinary officer Jan Slingenbergh, the researchers applied a modelling technique to establish how different factors contributed to spread of the virus, including the numbers of ducks, geese and chickens, human population size, rice cultivation and local geography. The numbers of ducks and people, and the extent of rice cultivation emerged as the most significant factors, even though the two countries had fought outbreaks in two different ways.

Strong link

The paper notes that there is a strong link between duck grazing patterns and rice cropping intensity. Ducks feed mainly on leftover rice grains in harvested paddy fields, so free-ranging ducks in both countries are moved to many different sites in line with rice harvest patterns,

In Thailand, for example, the proportion of young ducks in flocks was found to peak in September-October; these rapidly growing young ducks can therefore benefit from the peak of the rice harvest in November-December. Meat ducks are slaughtered around the Chinese New Year, a time when the volume of sales-related duck movement rises considerably.

These peaks in congregation of ducks indicate periods in which there is an increase in the chances for virus release and exposure, and rice paddies often become a temporary habitat for wild bird species.

The PNAS paper is not available yet, but should be in the next couple of weeks.  



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


btw I did send the link
to this diary to tptb, when I first wrote it.

Whether it got passed on to FAO or other relevant quarters is something that will remain a mystery.  ;-)



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
Indonesia
Interesting stuff Susan. There's plainly a piece of the puzzle missing still.

Can I ask if anyone knows whether the variant that is in vietnam this year is the same as the one in Indonesia?
The mortality rate in Vietnam is usually about 40 something % but its 100% this year.

I wondered if the clade 2.1 Indonesian variant had somehow reverersed course and headed north?

 Man occasionally stumbles over the truth.  Most of the time though, he manages to pick himself up and carry on as if nothing had happened.

Winston S Churchill


JK


don't know about 'this year'
Can I ask if anyone knows whether the variant that is in vietnam this year is the same as the one in Indonesia?

but up to 2007, the viruses in Vietnam belong to clade 2.3.4,  but the one in Indonesia is clade 2.1.

See Update on Avian Influenza A (H5N1) Virus Infection in Humans, WHO writing committee, NEJM, Jan 08, and Multiple Sublineages of Influenza A Virus (H5N1), Vietnam, 2005-2007 Nguyen et al, EID, April 08.



All 'safety concerns' are hypothetical.  If not, they'd be called side effects...


[ Parent ]
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