As the fight between a Ponoka man and federal veterinary officials continues over imported pigeons, concerns over whether the birds can transmit Avian Influenza to other species seems overblown.
Earlier this month, Guido Pfiffner was informed by the Canadian Food Inspection Agency that the 61 breeding pigeons currently in quarantine would need to be destroyed by July 13, unless the German government could validate that the birds were swab-tested for Avian Influenza (AI).
Dr. Faizal Careem, an associate professor of virology at the University of Calgary’s Faculty of Veterinary Medicine, in the Department of Ecosystem and Public Health, explained that the issue isn’t as easy or as black and white as it may seem.
“Influenza is kind of a strange virus. If one refers to textbooks, it says that pigeons are not susceptible to this virus and can not be carriers,” he said.
“But, since 1944 there has been tons of literature — both field and experimental studies — and they all say that pigeons are susceptible.”
In the past 74 years, 24 countries across four continents have conducted a total of 32 field studies and 22 experimental infection studies stated Dr. Careem.
“There are multiple studies, multiple authors and multiple countries involved, so I trust that data,” he added.
Dr. Careem explains that, in general, pigeons that carry the virus or antibodies — indicating previous exposure to AI — won’t show signs or symptoms.
“The most susceptible to the virus are wild waterfowl and shore birds, though the majority will only carry the virus and show no clinical signs. Pigeons are the same,” he said.
However, he noted that the virus is detectable in pigeons if it is present even though there are no clinical signs showing.
That testing is usually done in two ways: through taking a swab of the bird’s rear end or the nasal cavity; or via a blood test.
Carrier or transmitter?
Where the confusion comes in is on whether pigeons will transfer the disease to other bird species.
“There are some experimental infection studies that have been done with pigeons injected with the virus and then monitored to ensure they were excreting the virus. The pigeons were then co-habitated in the same cages as chicken and turkeys,” he said.
“What they found then was that none of the chickens or turkeys were infected.”
One reason for those results, as evidenced in the experimental findings, was that the pigeons didn’t secrete large enough doses of the virus to induce an infection into the far more susceptible birds they were placed with.
“Pigeons do have enough receptors that allow the virus to get into the birds, the issue is now that they have some form of natural resistance. That means the virus may be controlled to what may a be a low grade infection,” he added.
He also explained that it usually takes about a week for an AI infection to run its course in a pigeon and between 14 and 21 days for antibodies to show whether there is an infection or not.
Now while two big Avian Influenza strains — H5N1 and H7N9 — have made the news in recent years, there are literally hundreds of possible combinations as Dr. Careem noted there are 18 H subtypes and 11 N subtypes.
Yet, as influenza viruses are well known for mutating, Dr. Careem believes if the virus better adapts to pigeons it may well see the birds secrete vast amounts of the virus — large enough to infect other birds.
“That can happen, but we don’t know as there is no experimental evidence to suggest that is or has occurred,” he said.