A number of years ago, a friend who is a professor of biology at a large university in Canada, began to discuss the concept of "moving the zoo". What does this mean? Well, the idea is this. Whenever birds or animals, including human beings, are moved from one area of the country -- or the world -- to another area, they take with them a certain amount of biological baggage. This biological baggage can be likened very much to a zoo, because of the variety of biological creatures that exist within all living individuals. Thus, these individuals unwittingly carry with them, a number of biological agents, in effect, their own zoo, including various types of parasites, bacteria, viruses, molds, etc. -- whatever they happen to harbor in their bodies at the time.

Looking specifically at racing pigeons, one can see that whenever birds are imported from foreign countries, or if they are transferred from one side of the country to another, or even within one local area, or if birds from a number of fanciers are mixed together for racing, these birds carry with them, a certain complement of this varied biological baggage. So, for example, if birds have feather lice or mites, it is an easy matter for these external parasites to transfer to other similarly affected or unaffected birds in the same shipment, or to other birds at their final destination.

Many biological agents that make up this travelling zoo are innocuous, and their transfer to other birds is of very little consequence. The mixing of a number of similar organisms with different genetic backgrounds is a biological mechanism for the sharing of genetic material within the same species. Some of the newly transferred genetic material is beneficial to the survival of the species involved. Other genetic material that is transferred by the mixing of similar organisms of different origins may not be beneficial to these organisms.

However, as we all know from sad, and sometimes devastating experiences, the travelling zoo contains passengers that we wish could have stayed home. One of the best and most recent examples of a passenger that we would have preferred to avoid is the paramyxovirus (PMV-1). This virus, a very close relative of the virus of Newcastle Disease of chickens, surfaced first in the Middle East, moved through countries of the Mediterranean, spread into Europe and Britain, and finally into North America. Because viruses usually require living tissue in which to survive, this virus was transferred to susceptible pigeons in the tissues (likely the intestines and even the nasal tissues) of pigeons that were probably incubating the disease, ie, birds that were infected but not yet showing signs of the disease. The result was a massive outbreak of disease whenever infected pigeons were introduced to lofts of susceptible birds.

It is important to remember that when pigeons or other birds and animals are shipped anywhere, they undergo a period of considerable stress at this time. The brain sends messages of alarm to various tissues through the pituitary gland located on the underside of the brain. One key set of tissues to receive these alarmist signals is the adrenal glands located at the forward end of the kidneys. In turn, the adrenal glands send out chemical messengers in the form of steroids known as corticosteroids. One result of the action of these corticosteroids is the suppression of the immune (or defence) system. In this way, much of this defensive system is placed on lowered alert. When body defences are down, disease can strike.

Viruses that are hidden in body cells, are no longer controlled by a patrolling system of defensive cells and fluids, and begin to multiply. They escape from cells, and invade other cells. Millions of new viral particles are produced in this way, and many are shed in droppings, nasal secretions, etc., and by these means, are readily available to be picked up by exposed, susceptible birds.

More commonly than we realize, herpesvirus is a silent passenger among not only imported pigeons, but also among pigeons resident in North America. During periods of stress, it too begins to multiply in the tissues of infected birds. Like other viruses, herpesvirus uses the tissues of the bird as factories for the production of more and more viral particles. In effect, the living bird becomes a large factory, churning out viral particles in the millions. It will kill a few birds in a flock until general resistance builds to a level that protects the remaining birds. Like herpesviral infections in other species, including humans, even though most individuals become solidly resistant, a few will remain as permanent carriers, the virus safely hidden in tissues of the body until the next major period of stress allows them to begin to multiply and to be shed in droppings and other body fluids.

A relative newcomer to the racing pigeon scene is the agent called circovirus. This virus has only recently been identified in pigeons on this continent. Like the AIDS virus in humans, this virus appears to destroy important cells of the immune system, leaving the birds susceptible to a wide variety of other diseases. To illustrate this important point, case studies of this disease indicated that pigeons infected by circoviruses had a variety of other infections as well -- for example, those caused by Chlamydia sp. (the cause of a condition called variously, chlamydiosis, or psittacosis when it occurs in psittacine birds, and ornithosis when it occurs in other classes of birds, etc.), canker organisms, adenovirus, paramyxovirus, poxvirus, herpesvirus, molds, as well as infections caused by E. coli and Salmonella (paratyphoid) species of bacteria. This wide range of secondary and tertiary infections in pigeons known to be infected by circovirus points up the highly important role of this viral agent firstly in destroying defensive cells in the body, and secondly, in allowing a wide variety of other disease-producing agents to invade the tissues.

Luckily for all of us, the virus of Avian Influenza -- including some of the very deadliest strains -- which is common in waterfowl and other wild birds, just does not cause disease in pigeons, nor are pigeons implicated in the spread of this disease which is so important to our poultry industries. Scientific evidence is very clear on this point. This component of the biological zoo seems to find pigeons inhospitable, and it seems likely that, even in the face of bans on the movement of pigeons during an outbreak of the disease in domestic poultry, pigeons are highly unlikely to be implicated in the spread and maintenance of Avian Influenza.

Other agents involved in disease in pigeons operate generally in a similar fashion, attacking and invading during periods of stress. The organism that causes canker in pigeons is a small, teardrop-shaped parasite called Trichomonas gallinae that lives on the surface of the mouth, gullet and crop of pigeons. Under conditions of stress, such as the period following weaning in youngsters, or racing in old birds, etc., this organism can become increasingly active, and begins to multiply and to invade these surface tissues. Some of these organisms will also invade the liver where they produce severe disease that can kill, especially youngsters, but also old birds as well.

The organism that causes canker is interesting because it exists as a number of strains that range widely in their ability to produce disease. Some are completely innocent and produce only mild disease, or no disease at all in pigeons. At the other end of the spectrum, there are other strains in which the transfer of only a few organisms from one pigeon to another results in the production of severe, fatal disease. Experimental work many years ago by a man named Stabler showed as well that if the mouth, throat, gullet and crop of pigeons were colonized by a mild strain of the organism, this mild strain was remarkably effective in protecting against the introduction of a potent, disease-producing strain that would ordinarily kill.

On the subject of the canker organism, it seems that a number of the strains currently operating in Europe have become increasingly resistant to the usual drugs used in treatment.

This of course, increases the potential that strains of the organism that accompany imported pigeons soon or late will also gain a foothold in other parts of the world and may cause us untold grief in future. If we don't have useful drugs to combat this organism, should we consider a fall-back position of introducing innocuous strains into our birds -- as Stabler did so long ago -- to try to protect them against the new powerful organisms from other countries?

Moving the zoo becomes an important concept for any livestock operation that exports or imports animals or birds, whether nationally or internationally, and is no less important for us as pigeon fanciers. When we consider the great number of biological agents that we can introduce to our lofts through importations from foreign countries, through transferring birds locally and throughout the country, and through racing, we can see how relatively easy it is to move any number of biological zoos right into our back yards.

These zoos are only a phone call, a fax, Email, or a letter away from us.