Vietnam is once again reporting bird flu in chickens and ducks after no reports in poultry or humans since November of last year. I have not posted what I have been thinking during this lull, because I had no evidence to support it. But in truth I have suspected the virus has been quietly percolating away there beneath the radar screen. No reported outbreaks or cases doesn't necessarily mean the virus is absent.
I still have no evidence. But the virus has poked its head above water again:
At a conference held Tuesday by the National Steering Committee on Bird Flu Control, Cao Duc Phat, Minister of Agriculture and Rural Development and the committee's head, slammed the two provincial administrations for negligence and delay in discovering the outbreaks which had occurred at the start of December.On December 6 the disease broke out in Ca Mau's Tran Van Thoi district, killing 2,520 chicks and ducklings, all of which later positive for the deadly H5N1 strain of bird flu virus.
The next day five duck flocks took ill in Hoa Binh district in Bac Lieu. Some 3,500 ducklings died, all of which too tested positive for H5N1.
The committee claimed the dead birds had not been vaccinated because they had been hatched illegally. (Thanh Nien News)
Its easy to blame failure to vaccinate, and maybe that's right. But there has always been suspicion that vaccination masks infection in poultry without eliminating it. That might be sufficient to meet the needs of the poultry industry but if true, it still leaves, even creates, a public health problem.
H5N1 infections present as pneumonias. The causative agent for most clinical pneumonias is never determined. To diagnose H5N1 as cause requires specimens to be taken for viral isolation and then sophisticated laboratory tests to determine the agent. Most cases of pneumonia don't receive that kind of diagnostic work-up. It was the existence of a poultry outbreak in the vicinity that often was the factor triggering additional testing. If poultry vaccination eliminates the signal without eliminating the virus, we might have the picture we've seen over the last year in Vietnam: no visible outbreak unless there are unvaccinated birds.
But the virus doesn't spontaneously generate. It was there, waiting to be seen.
- Log in to post comments
According to Webster's figures from China, the biggest increases would be in ducks and geese and not chicken.
July 2005-June 2006, 2.4% of poultry in markets in China were positive for H5N1, of which chicken 0.5%, duck 3.3%, goose 3.5%. The year before that, it was overall 0.9%, chicken 0.2%, duck 1.3%, goose 2.0%
http://www.fluwikie2.com/index.php?n=Forum.NewDominantH5N1StrainInChina
I just listened to a presentation by Webster, he says that in Vietnam, vaccines were very effective and so there are no cases in chickens or humans, but there are infections in ducks and geese. He says 'Ducks are the Trojan horse".
One major problem has to do with grazing ducks, ducks that are let out to graze in rice paddies, where they pick up the virus from droppings from other birds. What's more these ducks are often taken on trucks to many miles away to graze.
What may make sense as 'sustainable farming' does not work for control of emerging zoonosis.
Duck manure is an oily, wet, forcefully expelled mess. (As opposed to chicken manure which is a small, not so soupy discrete pile. My poultry is all free range, but I stopped raising ducks years ago because the mess they make while roosting indoors away from predators at night was so nasty that it wasn't worth the effort.
As bad as free range duck may be, it's a darn site better than confinement duck-- now THERE's a virus factory for you!
Revere
STILL THERE, most likely, as you suggest.
Perhaps the best available technical reference on the AI vaccination efficacy issue is a 2004 paper from VACCINE by Ilaria Capua & Stefano Marangon entitled "Vaccination for Avian Influenza in Asia" (posted at http:\\oie.int/eng/AVIAN_INFLUENZA/vaccination%20in%20Asia.pdf).
The fourth paragraph of the paper states that experimental studies have confirmed that while the vaccination of poultry against avian influenza can prevent the appearance of clinical disease symptoms in poultry, vaccination against AI
- does not prevent poultry from becoming infected with avian influenza viruses,
- does not prevent poultry from transmitting avian influenza viruses to other birds.
Research studies presented at 6th International Symposium on Influenza in April 2006 confirmed this for the H5N1 virus in both ducks and chickens.
Recent threads in world media seem to point that H5N1 is poking it's head above water in many places.
I urge readers to look for news in: Ivory Coast, Turkey, Vietnam, and Egypt. Oh, and don't forget the continuing stories in Indonesia.
It seems like "Flu Season" all over again.
Add Nigeria and S. Korea to the list, while you're at it.
In terms of the issue of poultry vaccination for HPAIV, Japan presents an interesting case. The Japanese government has implemented a policy blocking the domestic use of poultry vaccines against HPAIV, precisely because there is evidence that vaccines are ineffective at completely blocking infection and viral shedding. Not surprisingly, the poultry industry in Japan has been lobbying forcefully for the loosening of these regulations. With four confirmed H5N1 outbreaks in S. Korea in the past month, it is very likely that Japan will experience another run-in with HPAI this season. Only epidemiological hindsight will ultimately demonstrate whether the Japanese government's policy was visionary or misguided, but in any case, Japan represents a notable departure from the mass vaccination strategy that has been implemented in China, Vietnam, and elsewhere.
Thank you and commenters, very informative.
Vaccination is effective in stopping mortality from avian flu. But it does not 'eliminate' the virus, ie it continues, *still there* though not so easily detectable. I wonder, is being easily detectable a sufficient justification for denying poultry growers their most effective defense? Given that avian flu is not eradicable by any definition, it seems to me that vaccination (using sentinels perhaps or other methods to improve monitoring) along with other tools (improving the outrageous conditions under which much poultry is produced in CAFOs) is the most feasible stategy for learning to live with this virus and its future strains. It's not going to go away.
ij: I planned to add them (and comment) tomorrow.