Several countries have elected to vaccinate poultry as a bird flu control measure. Vietnam and China both have such programs. The Vietnamese program is credited with their good record on bird flu this year. But poultry vaccination has some down sides:
The potential impact on human health of poorly implemented bird inoculations and experimental poultry vaccines needs to be carefully considered, according to a report prepared by the influenza team at the European Centre for Disease Surveillance and Control in Stockholm. A drop in the number of human cases in countries where fowl are vaccinated should "be interpreted cautiously,'' the report said."Surveillance for H5N1 cases in humans is becoming harder where poultry immunization is widely but imperfectly implemented because the marker of local poultry deaths for human case detection is being lost,'' according to the report published yesterday in Eurosurveillance, an online journal of peer-reviewed information on communicable diseases. (Bloomberg)
There are two distinct problems for surveillance. You lose the warning signal from poultry infections so you are not as vigilant for human infection and your diagnostic index of suspicion may be low, causing missed cases. And vaccination can mask infection in birds. Even if the vaccine works, the birds may still be infected and shed virus (although at much lower levels), but appear healthy. If the vaccinators are poorly trained or the vaccine is adulterated the vaccination may be ineffective, and the workers may even spread the virus by trekking it from farm to farm. There is suspicion this has happened in China and the Indonesian program is said to be poorly run and managed. With billions of birds requiring continuing vaccination each year the task is daunting and difficult to carry out successfully, even with adequate resources and political will.
No bird flu cases have been reported in Vietnam for six months. But this doesn't mean no one is getting sick from illnesses that might be avian influenza. There is currently a huge outbreak of dengue fever, a mosquito-borne illness whose diagnosis can easily be confused with influenza. A listing of dengue's clinical features shows why:
- Sudden onset of fever, severe headache, myalgias and arthralgias, leukopenia, thrombocytopenia and hemorrhagic manifestations
- Occasionally produces shock and hemorrhage, leading to death
Nearly 20,000 cases of dengue have been reported in the south of Vietnam in the first six months of this year, 54% more than the first six months last year (Xinhua). The outbreak is being blamed on poor household control of mosquito breeding sites.
One wonders.
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Revere.
Have their been disclosures as to whether the vaccines presently in uses are killed or live virus vaccines?
Tom's question, anyone?
The vaccination of poultry in countries known to have the bird flu is not an entirely effective technique. This issue, along with many others are discussed in the information presented by the American Council on Science and Health's publication "Avian Influenza, or 'Bird Flu': What you need to know"
http://www.acsh.org/publications/pubID.1294/pub_detail.asp
Since they are an effective inoculant, live-attenuated vaccines are commonly used in commercial settings to mass vaccinate poultry. For countries that unwisely use live-attenuated flu vaccine theres a probability of increasing virulence in the wild virus through recombination with the vaccine strains. Any idea who's admitting to still doing this?
While the 'backyard farmers' are always getting the blame, I suspect administrative policy enforcing the use of mass vaccination and anti-virals has driven flu recombination in Asia over the past 20 years. The lack of transparency means we can't track sequences to find out.
I expect we'll see the legacy of this over the next 100 years as the volatility of human primed flu adaptations oscilates through susceptible populations.
Jimmy, very interesting comment. Are live-attenuated vaccines ever delivered in water? How much water could you it dilute with before it lost it's effectiveness? What are the methods for "mass vaccination"?
When you mention flu recombination, are you using the term recombination in the general sense which would include reassortment or do you mean recombination within genes? Do you think it's possible for a live-attenuated vaccine to reassort with a naturally occuring virus?
Sorry for all the questions, but your comment touches on a subject I'm trying to find more about. Any help would be greatly appreciated.
Monotreme: I am only a layperson with rudimentary microbiology education so I can't give you expert answers.
I've been reading a few research papers about RNA recombination indicating that there is a risk of RNA recombination occuring between live-attuated viruses in vaccines and wild subtypes within cells in the vaccinated individuals. Either this recombination returns virulence to the vaccine strain or increases virulence in the wild strain. In particular the papers I've seen involve Polio and HIV for humans and SIV (Monkeys), FIPV (Felines) and BVDV (Bovines). I've read that this recombination can be homologous or non-homologous depending on the research/virus.
I don't know how the live-attuated viruses are delivered to poultry in Asia. From reading it seems that likely it's in feed.
Thanks Jimmy.
I just came across an article that seems to deal mostly with animal vaccines with some implications for human vaccines and some good references.
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1397843#B6
Expression of hemagglutinin protein from the avian influenza virus H5N1 in a baculovirus/insect cell system significantly enhanced by suspension culture
Nitar Nwe,1 Qigai He,1 Sudarat Damrongwatanapokin,2 Qingyun Du,1 Ivanus Manopo,1 Yukol Limlamthong,2 Beau James Fenner,1 Lynn Spencer,1 and Jimmy Kwang1
1Animal Health Biotechnology Group, Temasek Life Science Laboratory, 1 Research Link, National University of Singapore, Singapore 117604, Singapore
2Department of Livestock Development, National Institute of Animal Health, Chatuchak, Bangkok, Thailand
An excerpt:
Swayne et al. [5] suggested that vaccination has the potential to reduce environmental contamination with avian influenza virus and prevent subsequent bird-to-bird transmission [5]. In order to prevent spread of influenza viruses, emphasis must be placed on biosecurity and flock management practices, the development of rapid diagnostics [4] and vaccine production [6]. Current influenza vaccines include a subunit vaccine [7-10], attenuated vaccine [11,12], DNA vaccine [13] and inactivated influenza vaccine [14], with the latter being the most widely used on a commercial scale [6].
Kent: Thanks. This is related to the decreased viral shedding I mention.