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The EID report on wild birds indicated that H5N1 could be isoalted from lab infected birds for a one day period. Thus, collection of 200 samples over a six month period would not be expected to yeild more than one H5N1 isolate, even if all 200 birds were H5N1 infected during that 6 month time frame.
I don't understand what you mean.
"lab infected birds" ?
Why "one day period" ?
I don't understand what you mean.
"lab infected birds" ?
Why "one day period" ?
Here is the data on viral levels in swabs collected daily from individual birds. Most go from undetectable to detectable to undetectable in daily collections (detectable for just one day) in pharyngeal swabs (and not detectable at all in cloacal swabs)
Approximately one month ago testers of the Swiss bird control
took a saliva sample from a prochard, which wintered on the
Sempach-lake. With the animal no symptoms of the bird flu
showed up at that time. But now a complicated (intensive)
analysis resulted in that mentioned duck female had been
infected with the high-sticking on H5N1-Virus.
--------------------
Vor rund einem Monat entnahmen Kontrolleure der Schweizerischen Vogelwarte einer Tafelente, die auf dem Sempachersee ?berwinterte, eine Speichelprobe. Beim Tier zeigten sich damals keine Symptome der Vogelgrippe. Doch nun ergab eine aufw?ndige Analyse, dass besagtes Entenweibchen mit dem hochansteckenden H5N1-Virus infiziert gewesen war.
Here is the data on viral levels in swabs collected daily from individual birds. Most go from undetectable to detectable to undetectable in daily collections (detectable for just one day) in pharyngeal swabs (and not detectable at all in cloacal swabs)
For those who do not regularly look at scientific data, the data that look like teepees are individual birds which are negative on one day, positive the next day, and then negative the following day (H5N1 virus can only be isolated over a 1 day period).
These data highlight the limitations of surveillance, because similarly infected wild birds would only be positive for one day. Moreover, the data linked above was generated from wild birds that were infected in the lab. These experiments are well controled, so testing (and viral isolation) is done under ideal conditions. In the field, samples are collected, packaged, sent to one locaton for testing, stored during testing, and frequently re-packaged and sent to another location for confirmation, (which includes virus isolation). At each step, the sample can degrade and produce a false negative.
In the case in Switzerland, the positive was obtained until a month after collection. In the US (and elsewhere), testing is also frequently delayed by a host of factors.
For those who do not regularly look at scientific data, the data that look like teepees are individual birds which are negative on one day, positive the next day, and then negative the following day (H5N1 virus can only be isolated over a 1 day period).
It might be more accurate to say that, in this study, there were instances where H5N1 was isolated only during one 24 hour period. I don't think that extrapolating from their data collection scheme and small samples to a broad generalization of "H5N1 is only isolatable in wild birds during a 1-day period" is accurate; a better generalization is that this study suggests that there is not a uniform level of isolation of H5N1 across the period of infection.
It could be longer or shorter, but we don't know much more than what this study found: that they could test a bird one day and have it be positive, and not positive the day before or after. Does this represent a 1 day period of testability? No. It represents the limits of the testing scheme, done at 24-hour intervals. The bird may have only been positive for an hour during that day, or it could have been for almost 48 hours...
Even the asymptomatic birds that shed throughout the experiment (esp. orally) could be subject to similar non-uniformity. More experiments are needed with longer-term testing for these birds to figure out how long they might excrete virus, whether there are age-related effects, and with a larger number of birds to try and capture the variability that is present in all natural populations.
Hopefully this recent study is just the first of many investigating the complexities of H5N1, wild birds, and the testing/surveillance efforts...
It might be more accurate to say that, in this study, there were instances where H5N1 was isolated only during one 24 hour period. I don't think that extrapolating from their data collection scheme and small samples to a broad generalization of "H5N1 is only isolatable in wild birds during a 1-day period" is accurate; a better generalization is that this study suggests that there is not a uniform level of isolation of H5N1 across the period of infection.
It could be longer or shorter, but we don't know much more than what this study found: that they could test a bird one day and have it be positive, and not positive the day before or after. Does this represent a 1 day period of testability? No. It represents the limits of the testing scheme, done at 24-hour intervals. The bird may have only been positive for an hour during that day, or it could have been for almost 48 hours...
Even the asymptomatic birds that shed throughout the experiment (esp. orally) could be subject to similar non-uniformity. More experiments are needed with longer-term testing for these birds to figure out how long they might excrete virus, whether there are age-related effects, and with a larger number of birds to try and capture the variability that is present in all natural populations.
Hopefully this recent study is just the first of many investigating the complexities of H5N1, wild birds, and the testing/surveillance efforts...
Please. There were MANY birds tested under IDEAL conditions, and most were positive in ONE pharygeal collection and ZERO cloacal swabs, demonstrating that 200 wild bird collections over a 6 month period in Switzerland are a surveillance hoax (as are the 350,000 negatives by conservation groups).
AVIAN INFLUENZA (54): SWITZERLAND, OIE
**************************************
A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases
<http://www.isid.org>
Highly pathogenic avian influenza, Switzerland
----------------------------------------------
Information received on (and dated) 31 Mar 2008 from Dr Heinzpeter
Schwermer, scientist, Monitoring, Swiss Federal Veterinary Office,
Liebefeld Berne, Switzerland
Summary
Report type: Immediate notification (final report)
Start date: 22 Feb 2008
Date of 1st confirmation of the event: 26 Mar 2008
Date submitted to OIE: 31 Mar 2008
Date event resolved: 1 Apr 2008
Reason for notification: reoccurrence of a listed disease
Date of previous occurrence: June 2006
Causal agent: highly pathogenic avian influenza virus
Serotype: H5N1
Nature of diagnosis: Laboratory (advanced)
This event pertains to the whole country
New outbreaks
Summary of outbreaks Total outbreaks: 1
Outbreak location and affected population
Luzern (Oberkirch, Oberkirch): 2 tufted ducks (_Aythya fuligula_), one
common pochard (_Aythya ferina_), one mallard (_Anas platyrhynchos_) and 2
great cormorants (_Phalacrocorax carbo_) that were caught in a bird fyke
[net held open with hoops. - Mod.SH] on Lake Sempach.
These birds were sampled in the frame of the national programme for HPAI
and released after sampling.
The common pochard (_Aythya ferina_) that tested positive showed no
clinical signs of the disease at the time of sampling. The other birds
tested negative. Until now, there was no indication of the presence of
clinical infection in this region of Switzerland. This region can be
considered as one with the highest surveillance activity for avian
influenza virus in Switzerland. Since October 2007, 200 living birds have
been sampled and tested negative in that region.
Outbreak statistics
Species Wild species
Apparent morbidity rate 17 per cent
Apparent mortality rate 0.00 per cent
Apparent case fatality rate 0.00 per cent
Proportion susceptible animals lost* 0.00 per cent
*Removed from the susceptible population through death, destruction and/or
slaughter
Epidemiology: Source of the outbreak(s) or origin of infection. Unknown or
inconclusive.
Epidemiological comments: there was no evidence for a suspicion of HPAI at
the moment of sampling, as neither clinical signs nor an increase in
morbidity or mortality could be observed in the area (neither in wild birds
nor in backyard or farmed birds). Monitoring samples are typically analysed
in batches, explaining why the result was obtained only recently and
notified with a delay of about one month. The sequence determined (303 BP)
showed high homology to the viral sequences found in Eastern Europe in
2007. The obtained sequence at the hemagglutinin A cleavage site revealed
that the H5N1 strain detected was highly pathogenic, and the pathogenicity
index could not be determined.
In the past 5 weeks after sampling, no increased morbidity or mortality was
observed in wild or domestic birds in the area of Lake Sempach nor in other
regions of Switzerland. Proportionately to its wild bird population, Lake
Sempach is the best monitored water place in Switzerland, as it is the home
base of the Swiss Ornithological Station.
Nevertheless, measures were taken in line with the Swiss and European Union
legislation, and disease notification to the European Committee and to the
OIE was done, since the information about this isolated, random finding
might be of importance to the scientific community and to policy makers.
Laboratory name and type: Institut fur Viruskrankheiten und Immunprophylaxe
(IVI) (National laboratory)
Species: wild species
Test: polymerase chain reaction (PCR)
Test date: 26 Mar 2008
Result: positive
[This is an interesting case because the report emphasizes the observation
that there have been no clinical signs or excess morbidity or mortality as
one would expect in a previously non-infected area. If possible, since Lake
Sempach is the best monitored site in Switzerland, it would be useful to
know whether there was more than one wild bird which fell into this
subclinical but H5N1-positive status. If so, at what rate is this occurring
in different species living at the lake.
The location of the outbreak at Lake Sempach can be seen on the
HealthMap/ProMED-mail interactive map of Switzerland at
<http://healthmap.org/promed?v=46.8,8.2,5> or via the OIE report above. -
Mod.PC]
Please. There were MANY birds tested under IDEAL conditions, and most were positive in ONE pharygeal collection and ZERO cloacal swabs, demonstrating that 200 wild bird collections over a 6 month period in Switzerland are a surveillance hoax (as are the 350,000 negatives by conservation groups).
I'm not sure why you reacted so defensively--my comment pertained to your prior statement, which said
H5N1 virus can only be isolated over a 1 day period
, which came from your interpretation of the figure in the Keawcharoen et al. paper in EID. Unless you are talking about a different study, that interpretation is blatantly wrong, and I explained why in my post. You're missing the point: we don't know how long the window of testability might be. Whether it's one hour or 1 week is important to know in order to determine the level of testing needed to detect an outbreak.
I would argue that this is one of the most interesting tidbits that have come to light in the whole wild birds as vectors issue. We *know* that there is at least one asymptomatic H5N1-infected pochard out there in Switzerland. It's probably shedding (based on the limited data from the aforementioned EID paper).
Can we detect it in Lake Sempach?
Can we make any predictions on where an outbreak might occur, given the knowledge of at least one positive bird?
Could we proactively go out and capture more ducks to look at whether the infection is common across the waterfowl on Lake Sempach?
What about the birds thought to be vectors between waterfowl and (dry) barnyard poultry (house sparrows, jays, etc.)?
It just seems like a great opportunity to get some data to maybe understand the importance of one asymptomatic pochard...
As for there being many birds tested, the study in question tested 8 birds from 6 species=48 birds. I would reiterate my earlier comment that more experiments are needed to understand the implications for non-uniformity in our ability to isolate virus, both within and among waterfowl species. This study was just the tip of the iceberg...
I'm not sure why you reacted so defensively--my comment pertained to your prior statement, which said , which came from your interpretation of the figure in the Keawcharoen et al. paper in EID. Unless you are talking about a different study, that interpretation is blatantly wrong, and I explained why in my post. You're missing the point: we don't know how long the window of testability might be. Whether it's one hour or 1 week is important to know in order to determine the level of testing needed to detect an outbreak.
I would argue that this is one of the most interesting tidbits that have come to light in the whole wild birds as vectors issue. We *know* that there is at least one asymptomatic H5N1-infected pochard out there in Switzerland. It's probably shedding (based on the limited data from the aforementioned EID paper).
Can we detect it in Lake Sempach?
Can we make any predictions on where an outbreak might occur, given the knowledge of at least one positive bird?
Could we proactively go out and capture more ducks to look at whether the infection is common across the waterfowl on Lake Sempach?
What about the birds thought to be vectors between waterfowl and (dry) barnyard poultry (house sparrows, jays, etc.)?
It just seems like a great opportunity to get some data to maybe understand the importance of one asymptomatic pochard...
As for there being many birds tested, the study in question tested 8 birds from 6 species=48 birds. I would reiterate my earlier comment that more experiments are needed to understand the implications for non-uniformity in our ability to isolate virus, both within and among waterfowl species. This study was just the tip of the iceberg...
Please. The window of detection is VERY small, and testing 200 birds over a 6 month period is a hoax.
Please. The window of detection is VERY small, and testing 200 birds over a 6 month period is a hoax.
I'm glad you have faith in the duration of the window of detection. However, (and this is the last time I will bring it up), "VERY" doesn't really provide that much information that can efficiently inform action. Looking at the table you posted earlier (http://www.cdc.gov/EID/content/14/4/600-appG3.htm), you mentioned the teepees of data, and deduced there was a 1-day period of detection.
On the pharyngeal excretion portion of the graph there are few teepees, with their incidence increasing past 7 days. Some species (Tufted Duck, Mallard, Pochard) have one or less teepees during that first week, with detectable levels of H5N1. Interestingly, the detectability of all of the pochards decreases to zero on day 11, then springs back up for the remainder of the testing (3wks). So, for 20/21 days it was detectable in the study pochards via pharyngeal excretion.
Even on the cloacal excretion portion of the figure, three of the species (Pochard, Wigeon, Gadwall) show variation in the frequency of 48-hr teepees across the first week of the study.
So, in the context of the data that has been reported, I'm not sure what you mean by "very small"; are you referring to one of the species, one of the tests, or that you think anything between an hour and a couple of weeks should be considered very small? I posit that there is a big difference between hours and weeks.
I am a huge proponent of increasing surveillance (that was the main thrust of my last post-that there are a lot of opportunities for the swiss authorities to make a contribution by capitalizing on this asymptomatic positive); why not collect more experimental data to better target surveillance? It seems like a no-brainer...
Sorry if folks feel like this is a waste of bandwidth or a matter of semantics, but if we are to be an authority on avian flu we have to cleave to accuracy, and this issue of detectability, brought up time and time again in these forums (often by me ), is one of the least well-understood.
I'm glad you have faith in the duration of the window of detection. However, (and this is the last time I will bring it up), "VERY" doesn't really provide that much information that can efficiently inform action. Looking at the table you posted earlier (http://www.cdc.gov/EID/content/14/4/600-appG3.htm), you mentioned the teepees of data, and deduced there was a 1-day period of detection.
On the pharyngeal excretion portion of the graph there are few teepees, with their incidence increasing past 7 days. Some species (Tufted Duck, Mallard, Pochard) have one or less teepees during that first week, with detectable levels of H5N1. Interestingly, the detectability of all of the pochards decreases to zero on day 11, then springs back up for the remainder of the testing (3wks). So, for 20/21 days it was detectable in the study pochards via pharyngeal excretion.
Even on the cloacal excretion portion of the figure, three of the species (Pochard, Wigeon, Gadwall) show variation in the frequency of 48-hr teepees across the first week of the study.
So, in the context of the data that has been reported, I'm not sure what you mean by "very small"; are you referring to one of the species, one of the tests, or that you think anything between an hour and a couple of weeks should be considered very small? I posit that there is a big difference between hours and weeks.
I am a huge proponent of increasing surveillance (that was the main thrust of my last post-that there are a lot of opportunities for the swiss authorities to make a contribution by capitalizing on this asymptomatic positive); why not collect more experimental data to better target surveillance? It seems like a no-brainer...
Sorry if folks feel like this is a waste of bandwidth or a matter of semantics, but if we are to be an authority on avian flu we have to cleave to accuracy, and this issue of detectability, brought up time and time again in these forums (often by me ), is one of the least well-understood.
Most of the surveillance requires viral isolation for confimation. If just PCR was required, H5N1 in North America would have been reported when the three ducks died on PEI and one of one was H5 positive. After the press release and sample degradation, it was sent to Winnipeg and the degradation prevent verification, so no OIE report was filed and North America remained H5N1 free.
In this case Switzerland went with PCR and a partial sequence. There is no indication that H5N1 was isolated, and Switzerland has already signaled "case closed".
The birds that had more extensive H5N1 showed symptoms. The Swiss protocol was to catch healthy birds. Healthy (asymptomatic) birds are like those with teepees. H5N1 can be isolated for ONE day with pharygeal swabs, and can't be isolated at all with cloacal swabs in most asymptomatic cases.
For clade 2.2.3, the detection may be somewhat improved, which is why it was detected in feces in South Korea while Germany, Switzerland, and England have detected H5N1 in live birds (clade 2.2.3 is in Europe now, it was not in 2005/2006).
However, testing of 200 birds over a 6 month period remains a joke, especially since the lake has the most active surveillance in Switzerland.
Tweet
), is one of the least well-understood.
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