Comments re H5N1 Outbreaks and Enzootic Influenza

Just had quick look at review cited by promed as suggesting wild birds play role in spreading H5N1. H5N1">]H5N1 Outbreaks and Enzootic Influenza

With Robert Webster as lead author, I figured wild birds would get considerable blame, as he has seemed a gung-ho blamer of wild ducks - indeed, note re him says "The major focus of his research concerns influenza viruses in wild aquatic birds and their role in the evolution of new pandemic strains for humans and animals." (tho authors also include Guan Yi, who has been quoted saying wild birds not to blame, but convenient scapegoats). Doesn't seem wild birds tarred too badly.


Mechanisms of Spread

Were the highly pathogenic H5N1 viruses transferred within and between countries by persons, poultry, or fomites? In previous outbreaks of highly pathogenic H5 and H7 infection in multiple countries, the spread was directly attributable to humans. The main way influenza virus is spread in poultry is by movement of poultry and poultry products; establishing good biosecurity measures on poultry farms is therefore an important defense. The poultry industry is a huge, integrated complex in Asia, and a number of firms have branches in China, Vietnam, Thailand, and Indonesia. Nonetheless, the involvement of multiple lineages of H5N1 argues against human-mediated spread from a single source. Live poultry markets are an amplifier and reservoir of infection (18) and probably play a role in the maintenance and spread of the virus in the region. However, a number of other factors unique to affected Asian countries make control difficult. Backyard flocks are common in the region, and these domesticated birds are not subject to any biosecurity measures. Fighting cocks are prized possessions and are often transported long distances. Fighting cocks may also play a role in the spread of infection and in transmission to humans. Many of the affected countries have a weak veterinary infrastructure and are facing highly pathogenic avian influenza outbreaks for the first time. The migrant ducks that commonly wander through rice fields scavenging fallen rice seeds are another potent mechanism for the spread of infection.

do migrant ducks "commonly wander through rice fields"?? - in several places, I think, such wandering birds would be quickly shot or trapped.

The isolation of highly pathogenic H5N1 from herons, egrets, and peregrine falcons in Hong Kong in 2003 and 2004 leaves no doubt that wild migratory birds can be infected and may spread disease to local poultry flocks.

hmm; no doubt they can become infected - but why no doubt they can spread disease to local flocks; didn't spread among local wild waterbirds. The peregrine not wild: thought to be an abandoned bird, found in a park on Hong Kong Island

The outbreak in Qinghai Lake (16,17) proves that these highly pathogenic H5N1 influenza viruses are transmissible among migratory waterfowl. The migration route of shorebirds in the east Asian-Australasian flyway does overlap the areas that have had H5N1 outbreaks, although the virus has been notably absent in Taiwan, Malaysia (except for occasional outbreaks near the Thai border), and western Australia (Figure 2). The role of migratory birds in the transmission and spread of highly pathogenic H5N1 viruses is still unclear.

no, it's not unclear really; wild birds sicken and die, and H5N1 into wild birds is a dead-end; Mongolia shows that may get v rare further spread over distance, but all else shows this is indeed rare: "self-limiting in wild birds". As we know, the purported role is being perpetuated by FAO among others; good for scaremongering, and deflecting attention from real issues

Bad agricultural vaccines prevent disease signs but do not prevent shedding of transmissible levels of virus. They also promote undetected spread of virus on farms and to live poultry markets and promote antigenic drift. ... The clinical signs of infection with highly pathogenic H5N1 virus may be masked by cross-protection by other influenza subtypes, but this fact is often overlooked. During the initial outbreak of highly pathogenic H5N1 in Hong Kong in 1997, chickens in the live poultry markets exhibited no disease signs, yet samples from apparently healthy chickens, ducks, and quail showed highly pathogenic H5N1 in each of the poultry markets surveyed

I hadn't seen re this before; interesting

In conclusion:

perhaps the most insidious threat comes from unobserved transmission through wild and domestic ducks.

[nothing re fish farming - needs yet more highlighting]

I've emailed comments to authors (via form at bottom of webpage with the article) - hope I have better luck than when tried to reach Robert Webster via St Jude's. added note: No mention of potential role of integrated fish farming - dumping chicken manure into fishponds as feed/fertiliser, a practice encouraged by FAO and now spread to eastern Europe. Even feeding chicken offal to fish (Thailand, snakehead fish). Care with this: if mention, big loss of FAO brownie points.

Post edited by: martin, at: 2006/01/27 01:58

Share this

Vienna - Three cats were at one point carriers of the H5N1 bird flu virus in the southern Austrian province of Styria, but two of them have since rejected the virus, says a health official.

Re Cats surviving infection In Dutch experimental studies in which cats were infected with H5N1 virus all but one of the inoculated cats or cats in contact with experimentally infected cats survived. Therefore the Austrian findings (surviving infection) are not all that surprising and do not indicate any "adaptation" to this species. See Kuiken et al Science 2004 Oct 8;306(5694):241  
The cases in Europe again demonstrates that cats are susceptible to H5N1 viruses and some infected cats will die. Cat to cat transmission can occur when cats are kept in close proximity but is unlikely to lead to sustained natural transmission given the low "density" of cats in most households. In places where the disease is controlled in birds we will likely see the end of the disease in cats - as seems to be the case in Thailand. Regards, Les Sims Asia Pacific Veterinary Information Services

Hi Martin,

We have just initiated the Hong Kong node of the Asia Pacific Region Forum and would like to invite your participation in the formulation of a stance or proposal to any party interested in this matter defining the way forward, the cautions and so on in regard to Asian Flu as far as it concerns the small holder, home poultry keeping and wild birds.