WestNileVirus-L: Interesting piece in Toledo Blade today

From: Ellen Paul <epaul_at_concentric.net>
Date: September 16 2002

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Suggests that raptor situation is due at least in part to feather louse,
not WNV. 
 
 
Ellen Paul 
 
 
 Article published September 16, 2002 
Mysterious
plague exacts increasing toll on birds of prey 
 
By <a href="mailto:jenni@theblade.com">JENNI LAIDMAN</a>
 
BLADE SCIENCE WRITER 

<center></center>
 
A pair of great horned owls peer with wide eyes around the edge of their
shelter, like children sneaking a peek at a TV after their bedtime. 
 
But maybe they’re simply looking at what just hit them. Unknown numbers of
raptors - or birds of prey - are falling to an unprecedented plague this
summer. 
 
"I have this sense of a tsunami coming through the midsection of this country,’’
said Dr. Patrick Redig, director of the Raptor Center at the University of
Minnesota. "I don’t think it’s a stretch to assume the number of birds killed
by this is in the thousands.’’ 
 
This curious owl pair is among 21 Great Horned Owls still alive at Nature’s
Nursery in Lucas County. They are the lucky ones. Eighteen other raptors
delivered to the wildlife rehabilitation center since Aug. 12 died. 
 
Across the country, in a line that stretches from Maryland to Iowa, wildlife
centers are crushed by the demands of the formerly mighty raptors. 
 
The predators come in with heads bobbling, their balance shot, and sometimes
seizuring. Few rehabilitation centers have been as lucky as Nature’s Nursery.
Most birds die. 
 
"We received 67 birds. Seven are still alive,’’ said Mona Rutger, director
of Back to the Wild in Castalia. "The ones that are recovering are permanently
impaired.’’ 
 
The outbreak has many speculating that we’re seeing a new face of West Nile
virus. But if that’s the case, what’s changed? The virus has been in the
United States since 1999. Until this year, raptors were no more than occasional
casualties. 
 
So far, there are only theories, some with disquieting features that suggest
potential changes in the virus’ transmission pathways. One theory suggests
a new insect carrier. Another possibility is that raptors catch the virus
from their prey. 
 
While great horned owls seem to be the most at risk, red tail hawks, Cooper’s
hawks, kestrels, merlins, and even bald eagles have fallen. 
 
"The big question is, what has been the impact on the wild bird population,’’
said Dr. Kathy Converse at the National Wildlife Health Center in Madison,
Wis. But that’s just one of many questions no one can answer yet. 
 
Dr. Converse is trying to address a more urgent problem at the moment:
Why are these big birds dying? Her laboratory is overwhelmed with requests
for help. It receives 100 bird carcasses a day for analysis. Only a complete
examination of the dead animal’s organs, tissues, and fluids will reveal
what’s killing these birds. 
 
She frames her results thus far carefully: 
 
"A few of the raptors have tested positive for West Nile virus,’’ she said.
But a positive test does not confirm that West Nile killed these raptors. 
 
Testing positive for antibodies to West Nile only indicates the bite of
an infected mosquito. Many bird species, such as the ubiquitous house sparrow,
catch West Nile and never miss a wing beat. Most humans also show no symptoms. 
 
But even when a bird sickens from West Nile, the virus alone may not be
lethal. Another unrelated germ or toxin may team up with West Nile to weaken
the host. For instance, the Toledo Zoo veterinary staff thinks a combination
of avian malaria and West Nile may be attacking the zoo’s penguins. 
 
 Kay McKeever in Vineland, Ont., thinks she knows how West Nile arrived
to kill 74 of the 234 owls she breeds for release to the wild. And she’s
not blaming mosquitoes. 
 
She faults a bird parasite called the Hippoboscid fly. It’s actually a group
of flies also known as louse flies or flat flies. These insects feed on blood
in the quill of emerging feathers of large birds. 
 
"We had millions of flat flies. We’ve never, ever before seen anything like
this,’’ she said. She blames a mild winter that allowed most of the fly pupae
to live. 
 
"I think the Hippoboscid may have played a role, although we’re in the middle
of trying to investigate that’’ said Dr. Bruce Hunter, the wildlife pathologist
at the University of Guelph who’s worked with Ms. McKeever’s Owl Foundation
for about eight years. 
 
Dr. Hunter said it might be possible for the flies to carry West Nile on
contaminated mouth parts. He thinks it’s less likely that the virus can live
inside the flies the way it lives in mosquitoes. 
 
But he doubts these flies bring the virus to wild owls. 
 
"In this facility, there’s a heavy concentration of captive owls used in
a propagation program,’’ he said. Wild owls are dispersed, and therefore less
vulnerable. 
 
Yet a number of wildlife rehabilitation facilities have noted an increase
in Hippoboscid flies on the owls and hawks they’ve rescued. 
 
"There have been an inordinate amount of Hippoboscid flies. We have never
seen such an infestation [on raptors],’’ said Maggie Wright, manager of the
Lake Metroparks Wildlife Center in Kirtland, east of Cleveland. 
 
"I noticed early on, all spring and summer, an unusual infestation of them
on incoming birds,’’ said Ms. Rutger, of Back to the Wild. 
 
"Even in advance of the appearance of West Nile, we noted a heavy infestation
of Hippoboscid flies,’’ said Dr. Redig in Minnesota. 
 
But no one knows whether these observations have any meaning. 
 
"I know that it is a suggestion from some of the wildlife biologists,’’
said Dr. Emi Saiko, West Nile disease surveillance coordinator at the National
Wildlife Health Center. "We can’t discount it, but we don’t really know. I
don’t think anyone’s had the time to look at it yet.’’ 
 
At Nature’s Nursery in Lucas County, Laura Ponceby-Zitzelberger said she
has noticed no increase in Hippoboscid fly infestation. 
 
While bird deaths have been a hallmark of West Nile since it arrived in
the United States in 1999, it’s not clear West Nile has always killed birds. 
 
One other West Nile outbreak is identified with significant bird mortality,
and that was in Israel in 1998 . Research has since revealed the U.S.
strain of West Nile is genetically identical to the strain that caused the
outbreak in Israel. 
 
Most of the bird victims in the United States are in a family that includes
crows and blue jays. It appears any crow infected with West Nile dies from
it. And this brings up another theory of why raptors are dying now. Great-horned
owls in particular eat crows. 
 
"Sick and moribund crows would be easy pickings,’’ Dr. Redig said. 
 
One study suggests such disease transmission is possible. Dr. Robert McLane
with the National Wildlife Research Center in Fort Collins, Colo., put infected
crows in a cage with uninfected crows. All the crows died. 
 
"They excrete a lot of virus,’’ Dr. McLane said. A previous study showed
that infected crows caged separately would not pass the virus, suggesting
that at close quarters, the virus passes orally, not through the air. 
 
But even when West Nile fails to hurt birds, they are always part of the
picture in the advance of the virus. Bird-feeding mosquitoes spread the disease
among birds, and birds carry the virus when they migrate. 
 
While it’s not certain how West Nile first crossed the Atlantic to invade
the United States, the viral spread since 1999 has followed a zigzag pattern
that tracks bird migratory paths, said Dr. McLane. He andothers predict
birds will carry the virus south into Central and South America, if they
haven’t already. 
 
While it could be months and years before the larger scientific questions
about West Nile are answered, centers such as Nature’s Nursery and Back to
the Wild hope for some relief soon. Increased bird illness threatens to hobble
them. 
 
"Last year we had 1,713 rescues. As of today, we’re at 1,733, and last year
was our biggest year ever,’’ said Ms. Ponceby-Zitzelberger. 
 
"It’s putting a real drain on us.’’
 

 
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Received on Tue Sep 17 11:56:00 2002