Published Date: 2002-09-13 23:50:00
Subject: PRO/AH/EDR> West Nile virus, human - USA (CA) (04)
Archive Number: 20020913.5293

WEST NILE VIRUS, HUMAN - USA (CA) (04)
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Date: Thu 12 Sep 2002 4:45 PM
From: Charlie Calisher <calisher@cybersafe.net>


It was remarkable to see the first [confirmation of a] West Nile virus
(WNV) infection in a human in the western USA picked up by ProMED-mail from
a Chinese news agency, which had gotten it from NBC News. It is unlikely
that the report is completely accurate, in that it quotes a CDC
spokesperson as having said, "Migrating birds could have carried the
[virus] north from Central America or Mexico. Under that scenario, the
virus would probably have been detected in sentinel chickens or horses". I
doubt a CDC person would have said this.

First, there is no evidence that WNV yet occurs south of the USA in this
hemisphere, so it is unlikely that the patient in California was infected
by mosquitoes feeding on WNV-infected northbound migrant birds, which in
any event are not migrating north at this time of year. Second,
investigators have not had much luck detecting the presence of WNV using
sentinel chickens anywhere.

Perhaps what was meant is that in some quarters it is suspected that
inadequate surveillance for WNV south of our southern border may be
occurring and that WNV is already there but not being recognized. I would
worry at least as much about possible poor surveillance north of our
southern border.

--
Charles H. Calisher, Ph.D.
Red Feather Lakes, Colorado
<calisher@cybercell.net>

[Regarding the source being a Chinese news agency, you'd think that with
more than 17 000 US subscribers, somebody would have sent us the report
from a US source. Instead, it was left to our hardworking Epidemiology
Moderator to do a crash web search, and that was the first hit she got. It
is, word for word, what is in the Rocky Mountain News version and the AP
wire story, with the omission of a small but important detail -- there is
one more confirmatory test outstanding, the results of which may come out
while you are reading this on Friday 13 Sep 2002.

Certainly what Duane Gubler (the CDC researcher quoted in the previous
posting) was referring to in regard to bird migration was that the virus
may have traveled down to Mexico via the East Coast migratory bird flyway
last year (2001), overwintered there undetected, and returned via the West
Coast flyway. But while you may read such statements as "The yellow warbler
(_Dendroica petechia_) winters in the south of Mexico and as far south as
Peru and Brazil, then returns to Florida and California by April 1," that
doesn't necessarily mean that an East Coast bird down in Mexico, after
mingling there with the same species from the West coast, chooses to fly to
the West Coast -- it was hatched in the East, and instinct would take it
back there. There must be banding data to support this, but I don't have
the ornithologist contacts to confirm it.

Sentinel chickens were much maligned for their ineffectiveness in 2001, but
in 2002 they have been moderately successful, detecting WNV in 3 of the 7
states using them (Nebraska & Pennsylvania as well as all over Florida) --
see: <http://cindi.usgs.gov/hazard/event/west_nile/usa_sentinel_sep_11.html>

As for there being no evidence that WNV occurs south of the USA, that's not
surprising, as Charlie Calisher and Barry Beatty, with a group from the
Autonomous University of Mexico, are the only people I know who've been
looking for it there -- has anybody else done so? St Louis encephalitis was
not known to occur south of the border for many years, until it was looked
for in Brazil and Argentina. Surveillance for human cases of WNV in Mexico,
Guatemala, and El Salvador has only begun in the last few days, so they
have probably not been carrying out horse, dead bird, or mosquito
surveillance. I have e-mailed the El Paso Field Office of PAHO to try to
find out about WNV surveillance south of the border. If anyone has
information about such activities in Mexico, please send it. I will defer
to colleagues in Texas to respond to the question about surveillance just
north of the border. - Mod.JW]

See Also

West Nile virus, human - USA (CA): suspected 20020906.5247
West Nile virus, human - USA (CA) (02) 20020909.5265
West Nile virus, human - USA (CA) (03): confirmed 20020912.5286
............jw/pg/dk




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