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Pigeon Pox

Pigeon pox is caused by a virus belonging to the poxvirus group, a group of viruses that cause disease in many species. The avipoxvirus subgroup includes a number of closely related viruses such as fowl pox, pigeon pox and canary pox.

There are two clinical forms of pigeon pox, probably associated with different sources of infection. The most common method of transmission results from mosquito bites. Obviously, the resultant lesions will appear on featherless areas of the body, e.g. on the eyelids, around the beak and occasionally elsewhere on the body. The lesions start as small papules and gradually progress to a wart-like thick dark scab. Eventually the scabs will fall off and complete healing generally takes place within four weeks of infection. This form of the disease is seldom life-threatening and is often more of a nuisance in racing pigeons as it results in a break in the training program.

The second form of pigeon pox is probably due to droplet (aerosol) infection and involves the mucous membranes of the mouth, pharynx, larynx and trachea. This is often referred to as the wet form of pigeon pox as the lesions on the mucous membranes are soft and cheesy in nature. This is a far more serious form of the disease. Affected pigeons appear very sick, stop eating, have difficulty in breathing and generally lose a lot of weight. Mortality mostly results from asphyxiation due to blockage of the respiratory tract by the necrotic material or else from secondary bacterial infections with the formation of toxins.

Occasionally a mixed form may occur with cutaneous scabs as well as soft lesions in the respiratory or even the intestinal tract. This mixed form is more common in racing pigeons and may be due to the presence of predisposing conditions. The crowding of racing pigeons in baskets often leads to fighting with resultant skin lesions which will allow entry of virus. The very close contact between such pigeons will also facilitate contact transmission resulting in the cutaneous as well as the mucosal form.

To control pigeon pox, exposure to biting insects such as mosquitoes should be minimised or prevented. However, this is hardly possible especially during the racing season. The only practical alternative is to immunise pigeons before they can become naturally infected.

Vaccination, in most instances, amounts to controlled exposure of pigeons to field strains of virus by applying the virus to a part of the body where least damage would result. Squabs five weeks or older should be immunised. The directions for use described in the package insert that accompanies the vaccine should be carefully followed. There are basically two methods of vaccine application. In the one (scratch method) a hypodermic needle (supplied in the package) is dipped into the vaccine and one or two scratches made in the skin of the breast. This method requires some skill - if the scratch is too superficial, the virus will not "take" and no local lesion will develop. Should the scratch be too deep and a fair amount of blood exudes from the wound, the vaccine is flushed out, with no resultant "take". In the absence of a local lesion there is no certainty that the pigeon will develop immunity. This method is very popular with most pigeon fanciers but the immunity following vaccination is often variable as a result of the variable percentage of "takes".

The most effective method is the so-called "follicle method". About five feathers are plucked out on the lower leg and vaccine applied by means of a brush that has been dipped into the vaccine. Follicular lesions develop within 7-10 days and although the lesions may look unsightly for a few days, they disappear completely after 2-3 weeks. The general health of such vaccinated pigeons is not affected but the resultant immunity is of high quality and good duration.

From time to time complaints are received about the efficacy of the vaccine and suggestions are made about possible mutations in field virus leading to incomplete protection by the vaccine. It is highly unlikely that the failures can be ascribed to genetic mutations. Poxviruses in general are genetically very stable, and unlike influenza viruses are not prone to continuous genetic variation.

However, MEDPET will soon be conducting trials in cooperation with Dr Baltus Erasmus, a veterinary virologist from Deltamune, to compare field isolates of pigeon pox virus with the strain that is currently employed in the vaccine. Should the results indicate significant differences a new candidate will be selected to replace the current vaccine strain. MEDPET is looking into the possibility of supplying a brush with Medipox vaccine in future to enable users to utilise the follicle methods of vaccination.

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