WestNileVirus-L: Ornithologist responds re: human vectors

From: Ellen Paul <epaul_at_concentric.net>
Date: January 15 2003

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 In response to the comment that humans are not likely to be WNV
vectors: 
 
I'm equally baffled by the response. 
 
I'm not a medical doctor (and I don't even play one on TV), so perhaps I
just don't get it. But couldn't ANY host serve to move the virus? If I'm infected
and carrying active virus, and I get on a plane and go to Argentina, or any
place, for that matter, and I get off the plane and a mosquito bites me,
wouldn't that be as effective a source of transmission as an infected bird
flying to Argentina? 
 
What am I missing? 
 
I'm not clear how the fact that humans and other mammals are incidental
hosts makes any difference. There may be fewer infected humans than infected
birds,  but since most humans have, at most, a mild illness, it would seem
that we'd be more effective vectors. We'd be more likely to be able to travel
long distances while infected than would birds. 
 
What is the known range of incubation times in birds? It is my understanding
that WNV has been studied in the lab in only a handful of species of wild
birds - crows, mallards, Sandhill Cranes (the latter a vaccine study). We
would need to know more about the range of incubation times and the range
of the duration of migration (it varies not only with distance, but with species,
with weather patterns) to be able to estimate the probability that infected,
migrating birds could be vectors to a given place. 
 
Cleveland Parks Metrozoo has a statement (no research cited) that "WNV is sustained in a bird's blood
 stream for 1 to 4 days after exposure. After this incubation
 period, birds develop immunity against WNV." 
 
Scanning SIS and CRIS very quickly , I'm not coming up with anything on
incubation times or other species. 
 
So for instance, a bird that has arrived in Florida, replenished its body
fat for a couple of days, then gets bitten by an infected mosquito in Florida,
and, with favorable wind conditions and body conditions, departs that night
for a Caribbean island, would be more likely to make it than a bird bitten
in Maine that will fly from point to point along the coast or ridges of the
U.S., stopping for one or more days at each stopover location to eat and
wait for favorable conditions, and then continue in this manner across the
gulf or through Mexico, to points in South America ranging as far as Argentina. 
 
 
Ellen

<pre class="moz-signature" cols="$mailwrapcol">--
Ellen Paul
Executive Director
The Ornithological Council
<a class="moz-txt-link-freetext" href="Mailto:epaul@concentric.net">Mailto:epaul@concentric.net</a>
Ornithological Council Website: <a class="moz-txt-link-freetext"
href="http://www.nmnh.si.edu/BIRDNET">http://www.nmnh.si.edu/BIRDNET</a>
"Providing Scientific Information about Birds"</pre>
 
 
 
 
Environmental Risk Analysis Program wrote:

<blockquote type="cite"
cite="midp0520000dba4a1c2fab6c@%5B132.236.139.173%5D">A second batch of compiled
responses to the question posted yesterday (re: possibility of connection
between bird die off in Argentina & West Nile Virus): 
 
(4) 
From: Ashley Lovell  <a class="moz-txt-link-rfc2396E"
href="mailto:Ashley.R.Lovell@aphis.usda.gov"><Ashley.R.Lovell@aphis.usda.gov></a>
 
Date: Tue, 14 Jan 2003 
 
I find it surprising that a previous ornithologist* made the comment that
WNV might arrive in Argentina (or anywhere for that matter) via an infected
human.  It is quite unlikely that this would occur since humans, like horses
(for the most part), are incidental hosts.  Yet I see this statement made
in information publications, by scientists, and mentioned in the popular
media quite often, and it baffles me. In addition, it is plausible (and in
fact believed by many) that a bird infected with WNV would and could migrate
through its normal migration range.  Several species of birds that might
become infected with WNV are capable of migrating because incubation times
vary from species to species, and viremia levels vary from bird to bird.
 
 
Ashley Lovell 
USDA/APHIS - Wildlife Services 
1445 Federal Drive, Room 222 
Montgomery, AL  36107 
 
[*WestNileVirus-L  moderator's note: this is a reference to comments made
by Ellen Paul <a class="moz-txt-link-rfc2396E"
href="mailto:epaul@concentric.net"><epaul@concentric.net></a> #(3)
in the previous posting] 
 
 
(5) 
From: Timothy Male  <a class="moz-txt-link-rfc2396E"
href="mailto:tmale@environmentaldefense.org"><tmale@environmentaldefense.org></a>
 
Date: Tue, 14 Jan 2003 
 
Concerning the Argentine bird deaths, as the authors below note, it seems
unlikely that any of the species mentioned are migrants directly involved
in spreading the virus from North America to South America.  However, this
overlooks the more likely scenario in which migrants spread the virus to
South America and then the virus appears, potentially, in both resident and
migratory bird faunas. 
 
That said, it seems likely that this is not a set of bird species likely
to be indicative of a west nile outbreak (pigeons, for instance, are not
known for their wnv susceptibility nor are cardinals (Red-crested Cardinal
and Yellow-billed Cardinal are, I believe, non-migratory species present
in Argentina)) and seems more likely to be due to pesticide exposure.  If
bird mortalities continue, then perhaps there there would be greater concern
over wnv as the causitive agent? 
 
Timothy Male, PhD. 
 
Wildlife Scientist 
Environmental Defense 
1875 Connecticut Avenue, NW 
Washington, DC 20009 
 
(202) 387-3500 
(202) 234-6049 fax 
<a class="moz-txt-link-abbreviated"
href="mailto:tmale@environmentaldefense.org">tmale@environmentaldefense.org</a>
 
</blockquote>

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Received on Wed Jan 15 13:05:57 2003