# 1334
Today it was announced that the Saudi's won't attempt to cull pigeons in the Kingdom prior to the Hajj, because, according to Undersecretary at the Ministry of Agriculture, `Pigeons have Immunity against the disease'
Saudi spares pigeons
Saudi Arabian authorities have ruled out a cull of pigeons in Mecca and Medina despite the outbreak of avian flu in parts of the kingdom, reported Gulf News. A total of nearly 4m birds have so far been killed to stop the spread of the deadly H5N1 virus but Dr Mohammad Bin Abdullah Al Sheeha, an Undersecretary at the Ministry of Agriculture, said pigeons have immunity against the disease.
This certainly sounds definitive, and given the difficulties it would entail to rid the Kingdom of pigeons, is certainly good news.
But . . .is it true?
Are pigeons somehow immune? Do they pose no threat of harboring or transmitting the virus?
The record on this isn't quite as clear as the Saudi Minister would have us believe. I covered this story a year ago in The Origins Of The Feces, but there have been some newer studies, and so what follows is updated with new information
Pigeon fanciers would, of course, prefer it if pigeons were immune to the H5N1 virus. While many of us think of pigeons only as winged pests that infest our cities and bespoil statues in the park, to thousands of people around the world pigeons are beloved pets and are raised to race or show.
Many bird fanciers hang their hats on a report, published in Seed Magazine entitled The Invincible, Flu Immune Pigeon, published in May of 2006.
"Generally, you can't even infect pigeons, even with high doses [of the flu]," said David Swayne, director of the USDA's Southeast Poultry Research Laboratory. "If you give them high doses, occasionally you can get infected pigeons, but they usually don't shed very much virus."
Swayne has made it his business to shoot obscenely large doses of avian flu into pigeons' noses, using three strains of H5N1 in his experiments: The first, a strain found in Hong Kong in 1997, failed to infect even one pigeon, even when he gave them a far higher dose than they would ever encounter in nature. His other two strains were both found in birds isolated in Thailand in 2004, one a dead pigeon, the other, a dead crow. He nasally administered a high dose of the Thai strains to six pigeons each. Only one of these birds died. Six showed signs of infection but never became sick, and Swayne couldn't even detect the virus in the other five.
While seemingly putting the question of pigeon poop as a bird flu hazard to rest, many flu watchers expressed doubts.
In February of 2006, a 14 year old pigeon handler in Iraq reportedly died of the H5N1 virus, and in West Jakarta, a 39 year old man died in May of 2006, after reportedly cleaning pigeon feces from blocked roof gutters at his home.
And in this report from April 2006, a cat was infected after eating an H5N1 infected pigeon.
The case of H5N1 in a cat was reported during the early H5N1 outbreaks in Thailand in February 2004. The likely route of infection was eating an infected pigeon carcass. Our study confirmed H5N1 infection in pigeon carcasses from the same area. In our study, both H5N1 isolates from the cat and the pigeon displayed characteristics identical to H5N1 isolates from the epidemic in Thailand.
And in May of 2007, in the CDC's EID Journal, a dispatch appeared entitled Avian Influenza (H5N1) Virus in Waterfowl and Chickens, Central China, where scientists deliberately infected a variety of birds to determine their susceptibility to the H5N1 virus.
Early studies showed that pigeons were more resistant to the highly pathogenic avian influenza (H5N1) strain (A/chicken/Hong Kong/220/97; HK/220) than other birds (8). In our experiment, we demonstrated that isolates from 2004 could infect pigeons and could be reisolated from pigeon tissues, especially from glandular stomachs. Sequence analysis indicated that the avian influenza isolates used in this study and the HK/220 strain share high homology at the amino acid level for the HA (95%–97%) but not the NA gene (homology 79%–88%). This study indicates that the pigeon may be an asymptomatic carrier of avian influenza virus.
And the latest study, published in October of 2007, entitled Role of Terrestrial Wild Birds in Ecology of Influenza A Virus (H5N1) gives us this perspective.
Abstract
House sparrows, European starlings, and Carneux pigeons were inoculated with 4 influenza A (H5N1) viruses isolated from different avian species. We monitored viral replication, death after infection, and transmission to uninfected contact birds of the same species. Sparrows were susceptible to severe infection; 66%–100% of birds died within 4–7 days. High levels of virus were detected from oropharyngeal and cloacal swabs and in organs of deceased sparrows. Inoculation of starlings caused no deaths, despite high levels of virus shedding evident in oropharyngeal swabs. Least susceptible were pigeons, which had no deaths and very low levels of virus in oropharyngeal and cloacal swabs.
<snip>
Because pigeons shed only low amounts of virus upon infection and they did not transmit to contact birds, their role in the ecology of influenza (H5N1) virus may be minor.
So to review.
In Thailand, pigeons not only apparently died from the virus, they passed it on to an unlucky cat. It appears that two people in 2006 may have died as a result of exposure to pigeon feces, but both stories are anecdotal.
Lastly, scientists have managed to infect pigeons in the lab with the H5N1 virus, although they report that pigeons don't appear to be strong shedders of the virus. The latest studies indicate they may either be asymptomatic carriers or play only a minor role in the transmission of the virus.
Stating that pigeons have immunity to the H5N1 virus appears a bit of a stretch, although it does appear they are not as strongly affected by the virus as other bird species.
Of course, there are now reportedly at least five strains of the H5N1 virus running around Indonesia, with probably thousands of minor variants. Since we aren't getting virus samples, we have no idea if any of these mutated strains pose a greater risk to pigeons.
In Indonesia, as in China, we've seen some `immaculate infections', where no direct contact with sick poultry has been documented. Who knows how these people contracted the virus? Pigeon droppings are certainly one possibility.
The fact that pigeons seem to tolerate the virus does make one wonder if they aren't a silent reservoir of the virus, and that they may explain how the virus gets reintroduced back into an area after all infected poultry have been culled.
H5N1 is a moving target, and what may have been true yesterday may not hold true tomorrow.
Still, since we haven't seen huge die offs of pigeons in big cities or in famous pigeon haunts like the Piazza San Marco, nor have we documented H5N1 infections among any of the millions of yearly visitors who are exposed to these birds, I have to conclude the threat to the public is small.
At least for now.
At greater risk are pigeon handlers, and those whose job it is to clean up the mess left behind by these aerial bombardiers.
Today’s blog entry isn’t designed to invoke fear of pigeons, or inspire a rush to buy umbrellas.
It simply illustrates another conflicting data point in the continually evolving world of avian influenza.
