WEST NILE VIRUS & WEATHER (04)
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[1]
Date: Mon, 12 Aug 2002 08:43:06 EDT
From: John E. Andresen, DVM


The initial outbreak of WNV in horses on Long Island during 1999 followed a
hot, dry summer and a 2-day period of heavy rains in August.  Approximately
2 weeks after the rains, we began seeing horses displaying a variety of
neurological symptoms, initially diagnosed as St. Louis Encephalitis, but
confirmed WNV by the CDC in October 1999.  Literature about outbreaks in
Europe support the theory of drought followed by heavy rains.

--
John E. Andresen, DVM
Maribeth Andresen, RN, MPH
Mattituck-Laurel Veterinary Hospital
Laurel, New York, USA

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[2]
Date: Mon, 19 Aug 2002 12:49:52 -0400
From: Lois Levitan, PhD <LCL3@cornell.edu>


As we noted in our previous posting [to the WestNileVirus-L list-serv] on
the topic of weather as correlate and/or predictor of arbovirus disease
outbreaks, a number of related articles are referenced in ERAP's annotated
West Nile Virus Bibliography of Scientific Literature in
<http://www.cfe.cornell.edu/erap/WNV/WNVSciRefs(A-B).cfm> (use search term:
Infectious Diseases, Risk Factors).

This topic has come up previously on the WestNileVirus-L listserv, in
postings about WNV outbreaks in Israel, Russia, and Romania (see for
example: <http://www.cfe.cornell.edu/ERAP/WNV/WNV-LArchive/7-02-01c.html>
for more re: Israel, and
<http://www.cdc.gov/ncidod/eid/vol7no1/platanov.htm>
for more re: Russia).

The current outbreaks in Israel, in arid areas of the US, and the
amplification in the humid US Gulf Coast States provide additional fuel
(cases, data points) for this discussion and raise the question in my mind
re: the utility of distinguishing (as Paul Epstein noted in ProMED post West
Nile virus & weather (02) [see refs at end]) between:
(a) using weather as a predictor of initial amplification in a given cycle
and
(b) anticipating that these same weather correlates can also predict
geographic spread during the season and location of outbreaks throughout the
range, given the interplay among a sequence of other factors, including:

* extent of viral amplification in bird populations in the initial loci
* flight patterns of those species
* ecology and host preference of mosquito spp and length of mosquito season
in different areas, etc.

Note for example that Linn Haramis (in West Nile virus & weather (02) [see
refs below]) correlates hot dry weather with disease outbreak in the state
of Illinois, not across the disparate ecosystems in which we are seeing WNV
in 2002.

--
Lois Levitan, PhD
WestNileVirus-L moderator
Environmental Risk Analysis Program
Cornell University, Ithaca, NY, USA
<LCL3@cornell.edu>
<WESTNILEVIRUS-L@cornell.edu>

******
[3]
Date: Tue 20 Aug 2002 3:01 PM
From: Paul R. Epstein, MD <paul_epstein@hms.harvard.edu>


Further study regarding weather and WNV, SLE and EEE is certainly warranted.

Grady et al. [1] examined weather with regard to EEE [Eastern equine
encephalitis] and found that heavy rainfall preceded the 1955-56 and 1973-75
cases, thus rainfall might increase the prior probabilities of dormant eggs
hatching into large mosquito populations; but that many other factors (e.g.,
equine immunization) were involved. Edman et al. [2] provided background EEE
data for further examination of the connections. J. Freier [3] examined the
potential and complex role of climate change, warmer winters, and altered
breeding grounds for EEE.

For SLE [St Louis encephalitis], Monath & Tsai [4] suggested that drought
was associated with urban outbreaks, and our examination [5] of outbreak and
meteorological data revealed that 10 of the 12 urban SLE outbreaks before
1976 were associated with 2 months of drought (one of the other 2 with one
month of drought). These data suggest that, in the initial period of
establishing itself, SLE was amplified in urban settings by drought
conditions.

Regarding WNV, the recent history of large urban outbreaks associated with
droughts (Romania, Russia, Israel, the US) suggests the hypothesis that
intense drought across much of the US this spring and early summer [2002]
(see <http://www.noaa.gov/>) may have contributed to this year's
amplification and the significant number of cases. That Louisiana has been
so affected may reflect the June drought and July rains (boosting bridge
vectors), or Louisiana's position as a key flyover for migrating birds that
could have become infected elsewhere. A closer examination of cases,
meteorological data, and avian flyways may help elucidate the dynamics.

Social and genetic factors, ecological factors (e.g., the role of
potentially more tolerant "generalist" "scrap" birds, capable of sustaining
more prolonged viremia), and weather and climate undoubtedly all contribute.
In terms of meteorological factors, it may be the wide swings in weather
from intense drought to heavy rain or vice versa  prove the most
destabilizing to biological systems and the predators, food supplies, and
breeding sites for opportunistic pests and pathogens. Improved forecasting
of projected regional anomalies globally may help us better anticipate
conditions conducive to significant disease outbreaks.

--
Paul R. Epstein, M.D., M.P.H.
Associate Director
Center for Health and the Global Environment
Harvard Medical School
Boston, MA, USA
<paul_epstein@hms.harvard.edu>

References
1. Grady GF, Maxfield HK, Hildreth SW, Timperi RJ Jr, Gilfillan RF, Rosenau
BJ, Francy DB, Calisher CH, Marcus LC, Madoff MA. Eastern equine
encephalitis in Massachusetts, 1957-1976. A prospective study centered upon
analyses of mosquitoes. Am J Epidemiol 1978;2:170-178.

2. Edman JD, Timperi R, Werner B. Epidemiology of Eastern equine
encephalitis. J. Fla. Mosq. Control Assoc. 1993;64: 84-96.

3. Freir JE. Eastern equine encephalitis. The Lancet 1993;342:1281-1282.

4. Monath TP, Tsai TF. St Louis encephalitis: lessons from the last decade.
Am J Trop Med Hyg. 1987;37:40s-59s.

5. Epstein PR, Defilippo C. West Nile virus and drought. Global Change &
Human Health. 2001; 2:105-107.

--
ProMED-mail
promed@promedmail.org

[Mosquitoes that lay drought-resistant eggs do have population explosions
when the first rains come, but my understanding is that those species are
mostly aedines, & it is the culcines that are driving the U.S. WNV epidemic.
This inconclusive discussion is now closed. - Mod.JW]

[see also:
West Nile virus & weather         20020807.4984
West Nile virus & weather (02) 20020808.4997
West Nile virus & weather (03) 20020811.5019]
...................................jw/pg/jw


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