Birds as long-range WNV vectors

Dominick's supposition is certainly plausible. When I was working at
the Trinidad Regional Virus Laboratory, studying EEE (and other ARBO
viruses) in birds, the supposition was that North American migrants
would bring EEE to Trinidad and set up local infected populations.
Northbound migrants could then get re-infected before starting north in
the spring. As with most research, results were somewhat ambiguous.
Since we know that some birds that become infected with WNV get sick and
die fairly quickly, it's not those species that are going to carry the
disease to distant lands. What is needed is a bird that can support a
viremia, yet be resistant to its effects----a carrier, in other
words. There are lots of diseases where carrier states have been
identified in clinically well individuals (the Typhoid Mary phenomenon).

The flip side (ornithologic side) is to look at the candidate
species---the so-called "Neotropical Migrants". These include a variety
of passerine birds (mainly suboscine flycatchers and swallows, and
oscines: vireos, warblers, orioles, tanagers). It also includes a group
of non-passerine birds, mainly the shorebirds. Notably absent are
corvids. Bluejays migrate hundreds of miles. Crows are generally
considered non-migratory. They aren't the answer.

Most of the vireos, warblers, orioles, tanagers winter in Central
America, the Caribbean, or northern South America, leaving very few
species to get south of the Amazon (mainly some swallows and
shorebirds).

There are other ornithologic puzzles. For example, what birds would
have carried the virus so far west so fast. One possibility is that it
wasn't so fast---that the virus had moved westward 1-2 years earlier
than recognized. There are lots of birds that migrate from the
northwestern North America, southeastward in the fall. Some of these
might have carried the virus from the south (where it might circulate in
mosquitoes all winter), back to the north and northwest. But again, that
doesn't change the question about a carrier state. Another possibility
is that the virus was transported by road or rail, possibly in the form
of infected animals. Lots of good detective work still to be done.
It's a question of both WHO and HOW. MIKE GOCHFELD

"Ninivaggi, Dominick "
wrote:

> Dr. Wayne Crans at Rutgers has found evidence that EEE virus is reintroduced
> into New Jersey in the spring when migratory birds that were infected the
> previous year return. Apparently, birds can be infected and recover,
> complete their migratory round trip, and become viremic again (recrudesce)
> the following spring under the stress of mating season. The viremic birds
> then re-infect the local mosquitoes. If this is true for EEE, it would seem
> plausible that a bird could contract WNV in North America, recover, fly
> south and then infect mosquitoes in its "winter" home if something occurs to
> make the bird become viremic again. Needless to say, there is no evidence
> that this happens, but it seems plausible enough to a non-ornithologist like
> myself that it may bear looking into. However it happens, it is clear that
> WNV can spread rapidly, and there are no obvious reasons why t should not
> reach South America.
>
> -----Original Message-----
> From: Environmental Risk Analysis Program [mailto:envrisk@cornell.edu]
> Sent: Tuesday, January 14, 2003 3:28 PM
> To: WESTNILEVIRUS-L@cornell.edu
> Cc: promed@promedmail.org
> Subject: Ornithologists Respond #2 re: Bird die-off in Argentina & West
> Nile Virus
>
> 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 <Ashley.R.Lovell@aphis.usda.gov>
> 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 <epaul@concentric.net> #(3) in the previous
> posting]
>
> (5)
> From: Timothy Male <tmale@environmentaldefense.org>
> 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
> tmale@environmentaldefense.org
> --
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Received on Tue Jan 21 09:46:36 2003