Avian Influenza – a veterinary doctor's opinion

Culling wild birds will never stop Avian Influenza

Cyprus-based Dr Hugh A. Buck is both a veterinary doctor and founder member of the Oriental Bird Club. He offers the clearest explanation we have yet encountered of the relationship between wild birds, intensively-farmed poultry, and the spread of Avian Influenza.

This subject is understandably occupying a great deal of discussion space, and it perhaps needs a summary to cut through some of the conjecture and hysteria that surrounds it. I attempt this with credential as follows:

I am a veterinary doctor, as well as a serious birdwatcher. I work for an Animal Health Company which, among other things, specialises in vaccines for domestic poultry and ducks. I will try to put this as best I can in layman's terms (because in many ways I am, in this subject, a layman) but I have cleared it with my technical staff before release.

Much of the data comes from an excellent study entitled Avian Influenza: Ecology and risk factors for Humans and Poultry production by Dr Mauro Delogu of the Department of Public Veterinary Health and Animal Pathology at Bologna University in Italy. Mauro is a renowned virologist with a great interest in wild birds and, although the study was done in Italy, it is undoubtedly relevant to the rest of the world. I have also referred to the chapter on Avian Influenza by Easterday, Hinshaw and Halvorson in the standard work Diseases of Poultry 10th Edition (1997).

This disease is by no means new

The disease has been suspected for more than 100 years (first described in Italy in 1878), was studied intensively during the devastating ‘flu epidemics following the First World War, and has caused epidemics in poultry and other birds in many countries (including the USA and several in Western Europe) all over the world throughout this and the last century. It is likely it has also been overlooked in the face of other epidemic poultry diseases in the past, and only in recent years (the virus was finally identified in 1955), in parallel with a lot of birding, have the true identification techniques been worked out. Note that domestic pigs in Asia have also long been incriminated in outbreaks of "Asian" ‘flu in humans, so it should come as no surprise that intensively reared birds can also be a source. The virus has also been isolated from seals, a whale and a mink.

There is no question that Avian Influenza is, as its name suggests, largely a disease of birds. It is also clear from studies done that the virus is commonly found in wild birds, but the evidence is that it is primarily found in waterfowl and waders, and only rarely or never in other families. The presence of the virus does not mean that these birds suffer from Avian Influenza, as they are highly resistant, having developed high degrees of immunity over the millennia, and overt disease is rarely found. They are however carriers of the virus.

Dr Mauro Delogu's study sampled 21,000 wild birds of 88 species, 22 families and 12 orders. He found evidence of virus as follows (percentage of birds sampled):

Anseriformes – 15.2%
Charadriformes – 2.2%
Passeriformes – 2.9%

It is interesting to note the species breakdown in "anseriformes" (percentage of species sampled positive for virus):

Mallards – 63.9%
Other dabbling ducks – 31.4%
Diving ducks – 22.8%
Coots – 7.1%

In addition virus was demonstrated at a much higher level in post-breeding juvenile ducks than in wintering birds, which is logical. There was also a higher percentage in birds released from captive rearing than from birds collected from the wild.

Mauro also specifically sampled other groups, for example:

Terns – 3.6% positive in 140 birds sampled
Gulls – 18.8% positive in 101 birds sampled
Pheasant – zero positives from 424 birds (both wild and domestically reared)
Quail – zero positives from 258 birds trapped from the wild

Finally the virus is shed by birds' faeces in addition to other modes (such as respiratory).

Serotypes of virus isolated from wild birds do not immediately cause influenza in domestic birds

The influenza virus is highly mutagenic, that is, it can change in type and virulence very rapidly. This has long been known in human ‘flu, and is the main reason why there have never been (and probably never will be) truly effective influenza vaccines. The same is true of Avian Influenza – vaccines do exist and are (and undoubtedly will continue to be) widely used in attempts to control this disease. Their efficacy remains doubtful.

The serotypes of virus so far isolated from wild birds including ducks have been almost invariably low pathogenic and do NOT immediately cause influenza in domestic birds. In modern day intensive poultry units, the virus has however the distressingly rapid ability to mutate to high pathogenic forms, and this is the crux of the problem. This of course is a common phenomenon in highly crowded intensive situations anywhere – humans in the outback of Australia are less likely to suffer nasty new strains of Asian ‘flu than residents of Wanchai.

There is no evidence at all that humans can spread this disease to other humans

This pathogenic virus can spread from poultry to humans, although this is as yet rare. I stress that so far the human infections have only been in people directly in contact with diseased birds, there is no evidence at all that humans can spread this disease to other humans.

As birdwatchers, we have to accept that Avian Influenza can spread from wild birds, especially dabbling ducks, into domestic poultry. This may be by direct contact, for example wild ducks coming into contact with domestic ducks, which in turn come into contact with domestic chickens; or it may be spread by humans or domestic dogs (this is documented), who wander over fields contaminated with wild duck or geese droppings, and carry the virus into a farm.

The low pathogenic virus then has the ability to mutate into the high pathogenic form, and off we go. Highly pathogenic virus has been found, rarely, in wild birds (Mauro found it in one Herring Gull out of 100 sampled) but this, like the publicised dead Peregrine in Hong Kong and Open-billed Storks in Thailand was probably caused by contact with the pathogenic virus in poultry or poultry waste.

Wild birds are a scapegoat

Hysterical conclusions, statements and reactions, such as the outbreak in Indonesia being caused by migratory birds from China in August, or Bramblings falling out of trees in Thailand, are exactly that – hysterical and ill- informed responses. Avian Influenza can be spread into poultry from wild birds and can mutate into a pathogenic form, which can cause disease in both intensively reared poultry and humans. But the major transmission from farm to farm is unquestionably movement of infected poultry and poultry products, and wild birds are only a scapegoat.

At this moment the only veterinary solution to this problem is the rapid cull (kill) of all infected and in-contact birds, but this depends (remember the last outbreak of Foot and Mouth Disease in Britain) on an effective mobilised infrastructure to carry this out. This is probably not present in many of the countries where the disease is present, and this inaction will lead to epidemics.

The structure of the modern poultry industry almost guarantees these kinds of outbreaks in future

Vaccination of healthy non-infected birds is now being widely recommended and is underway in many countries, but we do not know the true value of this. We also do not know the future of this current "pandemic", and whether it will continue and get more serious, or whether the virus will change again and the crisis die down. What is likely however is that this disease will, like human ‘flu, continue to occur in outbreaks from now on. The structure of the modern poultry industry almost guarantees it.

What can birdwatchers do about Avian ‘flu?

We finally come to the question – what can we, as birdwatchers, do about it? Firstly, understand what is going on, which is what I have tried to summarise above. Secondly spread this understanding both amongst our friends and colleagues, and wherever possible, influential persons at Government and other levels.

Some of the reactions, such as in Thailand, do show some common sense being spoken, but we all know that this may not be the majority view. The message is that culling wild birds will never stop Avian Influenza. We might as well cull all the domestic chickens and pigs in the world, and we would still have human ‘flu.

There is however also, as several people have pointed out, a possible benefit in all of this: a reaction against the hunting, trapping and keeping of wild birds as pets. As birdwatchers, this possible benefit may outweigh the disadvantages.

Dr Hugh Buck