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Avian Influenza, Update Winter 2005

Dr. Paul G. Miller PhD, DVM
Pennsylvania Veterinary Laboratory

Avian Influenza, Update Winter 2005

By Dr. Paul Miller

 

For the past few months, Avian Influenza has been in the news, and some of this news has had a negative impact on the pigeon fancy.  This is an attempt to clarify and elaborate on some of that information, especially as it relates to pigeons.

 

The news media abound with fearful stories of some new and treacherous ‘Bird Flu’ that will ‘kill us all’, (more precisely 150 million) in the latest pandemic on the horizon, the worst since 1918.  Ninety nine percent of this is hype, intended to raise money for the medical bureaucracy establishment and improve business for drug companies and vaccine companies.  With West Nile fading fast over the horizon, the medical establishment needs a new poster child, a dreadful disease that will ‘surely kill us all’ if we don’t continue to support their capricious demands.

 

Some aspects of the current situation do raise concern, but we are light years away from anything remotely resembling a pandemic.  In Asia, over the past few years, there have been some cases of humans contracting Avian Influenza from birds; the earliest of any notoriety was in Hong Kong in 1997.  This infection was a H5N1 type which did indeed prove fatal in a few humans, but which did not infect pigeons and couldn’t be transmitted by pigeons.  (The ‘H’ and ‘N’ numbers are a technical way of characterizing the Influenza virus used by scientists to distinguish one type of Influenza virus from another; obviously if the numbers are different in two separate outbreaks, so are the sources of infection). 

 

As times have gone on from there, human infections of Avian Influenza have occasionally occurred in Asia; all of these have been in situations where there has been extremely close contact between humans and birds.  In many of these cases, the birds were chickens living in the same house as the person infected, often in hygiene and sanitary conditions far below contemporary American standards of personal and household hygiene and sanitation. As these people became ill, they were often diagnosed and treated using local medical professionals and facilities which, in some cases, are not comparable to American medical standards.  Under these conditions, the fatality rate of Avian Influenza in humans in Asia has been about 50%.

In most of this, the culprit has been H5N1 type Avian Influenza.  This particular strain of the Influenza virus is carried in wild waterfowl and shorebirds.  In the past, this virus has not caused disease in these birds, and,  as these birds migrate, they act as a wild reservoir for the disease, spreading it along their migration flyways.  Domestic birds which come into contact with the virus spread in this manner are likely to become infected, and many infected species are likely to develop disease.  With the relatively primitive poultry husbandry practices used in many situations in Asia, domestic poultry can easily become infected through exposure in this manner.

 

Over the past few years, H5N1 itself has undergone some changes.  Just as pigeons are subject to the laws of Genetics, so are viruses, and just as pigeon genes are subject to genetic mutations, so are viral genes subject to mutation.  Influenza is an RNA virus, and such viruses tend to have a relatively high rate of mutation.  Once a mutation has occurred, the persistence of that mutation is subject to the selection forces in the environment; a favorable pigeon mutation is selected for by the pigeon fancier to produce a winning flier or a show winner.  An unfavorable mutation is selected against and culled. Viruses work similarly, but with environmental forces doing the selection: virulent viruses more effectively infect their host, and are spread more efficiently.  Less virulent viruses are outnumbered and crowded out.  Hence, without any opposition or control, a virus would naturally tend to build up mutations enhancing virulence and it would increase in virulence, propagating more effectively within its host, transmitting more efficiently to another susceptible host and, possibly, even expanding its host range.  On the contrary, a situation in which the virus is not allowed to propagate widely would obviously not be favorable for any of this, and establishing a new viral mutation would be a very remote possibility.

 

 

This is exactly the situation with the H5N1 virus itself.  The H5N1 virus is found world wide, both in North America and in Eurasia.  Since the group of species of birds inhabiting North America is distinct from the group of species inhabiting Eurasia, these two groups of birds can be thought of as separate, distinct populations.  Also there is very little contact between birds endemic to these two areas; thus, these two populations of birds (American and Eurasian) can be thought of as entirely distinct populations of birds, each with its own unique environment.  Also, in each of these populations, the H5N1 virus experiences entirely different selective forces, and hence we have emerging two distinct strains of the H5N1 virus.  Just as there are different strains of racing pigeons (e.g. Sions vs Jansens), there are emerging different strains of the H5N1 virus. 

 

In particular, as we have seen above, in Asia, there has been very little effective control over the H5N1 situation, so it has propagated largely out of control, and hence become a distinct, more virulent strain of the H5N1 virus; thus the Eurasian strain of H5N1 has now been specifically named ‘Asian H5N1 HPAI’.  (The ‘HPAI’ stands for Highly Pathogenic Avian Influenza).  The Asian H5N1 HPAI strain lives up to its name very well.  It is pathogenic in its natural hosts (waterfowl and shore birds) and, can still infect humans,  cause disease and even death.  Unfortunately, it has also extended its host range to now include pigeons.  This does not mean that pigeons have become its natural host, but it now can infect pigeons and cause disease in them.  Pigeons are still insignificant players in the Eurasian H5N1 scene, but they are now in the host range.

 

In contrast to the Eurasian situation, the American H5N1 remains well controlled.  It has never had the opportunity to become highly pathogenic, mainly because it has been stamped out or controlled where ever it has been found.  For foreign trade as well as public health reasons, the United States and Canada have always aggressively stamped out or tightly controlled Avian Influenza (regardless of H and N types)  whenever it occurred.  In this environment, it has not had the opportunity to become highly pathogenic, hence the American H5N1 is termed LPAI, Low Pathogenic Avian Influenza.  For this American H5N1 strain, the prior experimental results would indicate that pigeons are largely resistant.  Notice that, as much as we dislike government intrusion into our lives, both state and the federal government play a major role in defining this environment, especially keeping Avian Influenza from getting out of hand as it has in Asia.

 

So where does this leave us ???  Obviously that depends upon the geographic location.  In the United States and Canada, the situation is as it was before: the American H5N1 has low pathogenicity, and pigeons (and humans) don’t get it.  That doesn’t mean that we can become complacent and forget about Avian Influenza; we still need to be very vigilant and make sure that all Avian Influenza is well controlled so that we don’t get into the situation we have in Asia.  In particular, let me reiterate a few precautionary principles.

 

·        Do NOT let your birds mix with migratory birds, especially waterfowl or shorebirds.  All wild birds should be kept out of your loft and off your premises.  Do NOT feed wild birds around your pigeon loft.

·        Do NOT let your birds mix with any other domestic poultry; galliforms and waterfowl can and do get Avian Influenza, and could set up a situation similar to the Asian situation, expanding the host range into pigeons.  Don’t let this happen.

·        Do NOT allow your birds to mix with feral pigeons, and do not allow feral pigeons into your loft.

·        Avoid any and all contact with hogs, even indirect.  Hogs are the ‘mixing vessel’ to combine the Avian Influenza strains with human adapted strains.  Many of the Avian Influenza cases I have seen in domestic poultry have been associated with hogs.

·        When training, keep birds under control, and do NOT allow them to just sit around outside on the loft roof; they should be either in the air or in the loft.  Young birds traveling to scout the territory is fine, as long as they are flying.  Except for settling, birds should not just sit on the roof.

·        Races and training flights should be arranged so that the birds can make it home in a reasonable amount of time.  Do NOT release into bad weather, weather ‘fronts’, low atmospheric pressure, high winds, other races crossing their flight path, etc.

·        Do NOT import pigeons from Europe, except through approved USDA quarantine stations.  Since the Asian H5N1 HPAI can infect pigeons, we must be VERY CAUTIOUS with anything from Europe.  There are plenty of good birds available domestically; it is no longer necessary to import from Europe.

·        In the case of an Avian Influenza break in any species, keep yourself and your birds totally clear of any contact, even indirect or incidental.

 

In the Asian situation, the strategy would be to keep pigeons as a minor, incidental host.  Pigeons are not a major player in Asian H5N1 HPAI at this time; they are insignificant at this point.  Keep it that way.  Do not allow pigeons to become infected, and quickly destroy any that do become infected.  Monitor for Avian Influenza by whatever means are available through your local Avian Lab or Avian Vet; and vaccinate if a vaccine becomes available and is approved.  The above rules should also be observed, and modified as necessary to fit the situation.

 

Avian Influenza is not a major problem in pigeons.  With a little bit of common sense and vigilance we can easily keep it that way, and continue to enjoy our birds for a long time to come.  Good luck.