Monday, May 04, 2015

Can Bald Eagles Get Avian Influenza?

Can bald eagles get avian influenza? That question is increasingly being asked of us at Ustream and on Facebook. The short answer: We don't know. But let's take a quick look at the landscape so far.

What is avian influenza?
To quote the USDA: "Worldwide, there are many strains of avian influenza (AI) virus that can cause varying degrees of clinical illness in birds. AI viruses can infect chickens, turkeys, pheasants, quail, ducks, geese and guinea fowl, as well as a wide variety of other birds. Migratory waterfowl have proved to be a natural reservoir for the less infectious strains of the disease.

AI viruses can be classified as highly pathogenic (HPAI) or low pathogenic (LPAI) strains based on the severity of the illness they cause. HPAI is an extremely infectious and fatal form of the disease that, once established, can spread rapidly from flock to flock."

There are at least two different HPAI strains circulating right now: EA/AM-H5N2 and EA-H5N8. The USDA tells us that: "The H5N8 virus originated in Asia and spread rapidly along wild bird migratory pathways during 2014, including the Pacific flyway.  In the Pacific flyway, the H5N8 virus has mixed with North American avian influenza viruses, creating new mixed-origin viruses.  This is not unexpected.  These mixed-origin viruses contain the Asian-origin H5 part of the virus, which is highly pathogenic to poultry.  The N parts of these viruses came from North American low pathogenic avian influenza viruses." The same thing appears to have happened in the Mississippi flyway with H5N2. It is generally believed that waterfowl migrating north carried the virus into Minnesota, although it isn't known how it spread to confined poultry. They most likely contracted the virus while wintering in areas shared with infected Pacific flyway birds.

At present, the USDA reports that:

  • 114 avian flu detections have been reported.
  • 21,644,473 animals have been affected. The vast majority have been on commercial poultry farms that raise chickens, turkeys, mixed poultry, and pheasants.
  • The first detection was reported on 12/19/14 and the last detection was reported on 05/01/15.
While most of the detections have been reported in commercial poultry, wild birds can contract H5N2 as well. The vast majority of cases have been reported in waterfowl, including wigeon, canada geese, mallard ducks, wood ducks, northern shovelers, and teal. Unfortunately H5N2 has also been reported in birds of prey, including:
  • Coopers hawks
  • Red-tailed hawks
  • Gyrfalcons
H5N8 has been reported in:
  • Peregrine falcons
  • A bald eagle
  • A great horned owl
  • Gyrfalcons
On April 30th, Minnesota Public Radio reported that a Cooper's hawk in Yellow Medicine County was the first Minnesota wild bird to test positive for the avian influenza virus H5N2. However, a positive test from a dead raptor only means the bird was exposed to the virus, not that the virus killed it or that the bird spread the virus to other birds. In this case, it was killed when it flew into a window and the virus was found after the carcass was sent to The National Veterinary Service Laboratory in Ames, Iowa.

So what can we make of all this? Based on what we know now, the eagles in Decorah and Fort St. Vrain don't appear especially likely to succumb to H5N2 avian influenza.
  • While H5N2 can be spread through consuming infected prey, it has tended to spread in domestic animals after direct contact with fecal droppings or respiratory secretions of infected birds. This is less likely to happen in a highly dispersed bird like the bald eagle. The virus has only been reported in one bald eagle and a small handful of wild raptors.
  • No large die-offs of raptors have been reported in Minnesota, Iowa, or Wisconsin. All three states are conducting surveillance programs to identify to what extent the virus is present in wild birds.  
  • While waterfowl can carry the virus, it seems to primarily affect domestic large-scale operations. Backyard flocks of chickens have not been infected to nearly the same degree. The USDA has identified just 12 cases in backyard flocks, including five in Washington in January and February, plus others in Idaho, Kansas, Minnesota, Montana, Oregon and Wisconsin. Wild and backyard birds could have been exposed over time to low pathogenic versions of bird flu and developed stronger immunity as a result.
It is believed the virus will die as temperatures warm up and ultraviolet light increases.  In the meantime, I suggest the following links for more information, including influenza updates: 
How are states responding?
News Articles

Did you know?
In Minnesota, the DNR is working to identify the virus in wild birds. The agency is collecting waterfowl fecal samples throughout Minnesota; asking turkey hunters from Kandiyohi, Pope, Meeker, Swift and Stearns counties to submit their harvested wild turkeys for testing; and collecting dead birds of various species reported by the public. 

The DNR has collected 29 dead birds of varying species; nine have tested negative for the virus and 20 results are pending. Test results also are pending on the 37 samples from hunter-harvested wild turkeys. The agency has collected 2,749 waterfowl fecal samples – nearing its goal of 3,000 – and more than 2,200 have tested negative; results for the rest are pending. The waterfowl fecal sampling effort is designed to determine with 95 percent confidence whether the virus is present on the landscape in at least one percent of the waterfowl population. They really want to know if you find a dead turkey or raptor. Go to http://www.dnr.state.mn.us/avianinfluenza/index.html for more information.

The Raptor Resource Project has offered to collect samples while banding this year. I'm guessing the answer will hinge on whether or not we start seeing problems in the wild population. We will keep you informed if anything happens.

2 comments:

Nora H said...

Good writing Amy. What I can't figure out is how the big poultry barns contracted it being they're shut in the buildings. I can see where it would really spread inside there if one was affected by it. Thanks.

AmyRies said...

Nora, that's a big mystery to everyone. Fecal material can be very fine - almost aerosolized - and carried on clothing. While the chickens and turkeys don't have contact with other farms, I've wondered if some of the human workers and owners do. I hope it is figured out.