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The Potential for the Emergence of Dengue The Potential for the Emergence of Dengue Fever in the S.W. United States along the Fever in the S.W. United States along the
International BorderInternational Border
Mary Hayden, Ph.D.
University of Colorado
July 23, 2004
NISSC
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Study Objective
To examine the impact of climate variability and human-environmental interaction on the proliferation of Aedes aegypti, the mosquito vector for yellow fever and dengue fever, in a desert region.
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Background
Aedes aegypti is the principal vector of yellow fever and the dengue viruses.
The etiological agents of dengue and dengue hemorrhagic fever are four antigenically related, but distinct viruses.
DEN 1, DEN 2, DEN 3, and DEN 4 are classified in the genus Flavivirus, family Flaviviridae.
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Dengue Fever
All four serotypes cause disease characterized by:
Sudden onset of headache Fever Myalgia Anorexia Arthralgia
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Dengue Fever
The incidence of dengue fever has increased dramatically in the western hemisphere since the 1970s.
The virus is maintained in an endemic/epidemic cycle with epidemics occurring every 3-5 years in the developing world.
Documenting the spread of the vector into the desert Southwest, and its interaction with climate, local ecology, and human behavior is critical to prevention of the spread of the virus.
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HCP/HCT/VBD
PAHO/WHO 2002
JRA
Reinfestation of Aedes aegypti1930s 1970 2002
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HCP/HCT/VBD
PAHO/WHO 2002
JRA
Aedes aegypti:Distribution
throughout the world
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Distribution of Aedes aegypti in the United States, 2001
Positive
Negative/Eradicated
Intercepted
Unknown
Current status
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Study area:Tucson, Arizona-Ambos Nogales corridor.
Tucson
NogalesArizona
Mexico
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Three Study Sites
Tucson, AZ – 2410 ft.; population 486,699 (2000 census)
Nogales, AZ – 3865 ft.; population 20,878 (2000 census)
Nogales, Sonora - The official population of Nogales, MX is 180,000, but unofficially estimates are as high as 400,000.
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Nogales, AZ – adjacent to border
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Study Aims and Methods
Analyze spatial/temporal land use and conduct field inventories of facilitators/inhibitors of human/mosquito interaction.
Conduct mosquito surveillance 5x annually to include coldest, driest, and wettest months.
Evaluate climate variability at 68 sites. Collaborate with public health personnel.
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Measures
Current satellite imagery has been examined to determine land use, utilities access, and overly-irrigated sectors.
Photographic documentation of environment within 50 meter range of ovi-traps has been produced.
Field inventories have been conducted of facilitators and inhibitors of mosquito/human interaction.
Oviposition traps have been set up 5x annually – 21-24 sites in each locale. Trapping periods relate to climate. One week in Jan. (coldest), one week in May (driest), and one week each in July, Aug. and Sept (monsoon).
Hourly temperature and dewpoint data have been collected for two years at 68 sites using data loggers.
Seven additional sites were added in 2003.
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Collaboration with Public Health personnel
Increase community awareness of dengue fever. Border Infectious Disease Surveillance (BIDS) has begun to test for dengue in the border regions. Thirty cases in Sept./Oct. 2003 in Nogales, MX.
Raise physician awareness of outbreak potential.
Reduce vector breeding sites through community/household intervention/participation.
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% Positive Traps by Site
0
20
40
60
80
100
120
Nogales, MX Nogales, AZ Tucson, AZ
Sites
Per
cen
t
2002 positives
2003 positives
% pos. in yr. 2 alsopos. in yr 1
Results of Ovi-Trapping
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Number of Positive Sites by Month, 2002 & 2003
0
10
20
30
40
50
60
June July August September
Nu
mb
er
of
Sit
es
2002 2003
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Characteristics of Study Sites
Ecology of Study Sites
010203040506070
Nogales,MX
Nogales,AZ
Tucson,AZ
Sites
%
% irrigating aroundhouse
% evaporativecooling systems
% with > 25%vegetationcoverage*
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Temperature
0
20
40
60
80
100
120
2002 2003 2002 2003
MinimumTemperature (F)
MaximumTemperature (F)
Tem
p (
F) Nogales, MX
Nogales, AZ
Tucson, AZ
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Results: Differences Between Sites
Socioeconomic differences between Mexico and U.S. related to patterns irrigation, vegetation around houses, and mechanical cooling systems.
Tucson is hottest, the areas between Nogales, AZ and Tucson are coolest, and Nogales, MX lies in between.
The mosquito is present in all areas. Sites positive in 2002 were likely to be positive in
year two. Two measured factors differentiate between positive
and negative sites: minimum temperature and presence/absence of an evaporative cooler.
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Eggs and Positive Sites by Minimum Temperature, 2002-2003
02468
1012
60-65.4 65.4-68.4 68.4-69.9 69.9-71.5 71.5-75
Temperature (F)
Sq
uare
Ro
ot
of
Eg
g C
ou
nt
0.00
5.00
10.00
15.00
No
. o
f P
osit
ive
Sit
es
Pos Sites Square Root of Eggs
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Number of Positive Sites by Presence of Swamp Coolers
05
1015202530
Both Years Year One Year Tw o
Period of Data Collection
Nu
mb
er
of
Sit
es
Yes No
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Variable Positive in 2002 Positive in 2003 Positive Both Years
Odds Ratio 95% C.I. Odds Ratio 95% C.I. Odds Ratio 95% C.I.
Minimum temp (F)
1.36* 1.03-1.79 1.503* 1.01-2.24 1.54* 1.05-2.25
Evaporative cooling
7.61** 1.68-34.5 2.95 2.55-15.91 8.80* 1.61-48.25
Controlling for humidity, location of site, and maximum temperature.
Presence/absence of Swamp Cooler, Average Minimum Temperature Predict Presence of the Mosquito
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Conclusions Ae. aegypti is well-established in this region, suggesting the
successful re-invasion of a dry, desert environment by a tropical species of mosquito.
The mosquito breeds seasonally, with the greatest activity noted during the more humid monsoon season. Whether the mosquito over-winters, or re-colonizes the area every summer is a question that needs to be addressed through more detailed ecological and genetic studies.
Presence or absence of amenities, irrigation patterns, and vegetation cover are not related to the presence or absence of the mosquito.
Quantitative findings suggest that breeding activity is linked to higher minimum temperatures, especially over 69˚ F. and the presence of an evaporative cooler.
Low levels of window and door screening in all study sites, coupled with the identification of positive dengue cases in Sonora, Mexico, suggests a significant potential for an outbreak of dengue fever.
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Aedesaegypti
ClimateVariables
Land Use
Numberof Breeding
Sites
Access toAmenities
Swamp Coolers
Factors in Mosquito Proliferation in the Sonoran Region
Water Storage
Sanitation
SewageMigrationto border
region
Populationincrease
Cross-bordermigration
Minimum
temperatures > 69°F
Human behavior
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Collaborators
Andrew Comrie, University of Arizona Mercedes Gameros, Binational Office, Sonora MX Duane Gubler, Centers for Disease Control Henry Hagedorn, University of Arizona Karen Kafader, University of Colorado Craig Levy, Arizona Department of Health Services Linda Mearns, National Center for Atmospheric Research Rafael Moreno, University of Colorado Frank Ramberg, University of Arizona Cecilia Rosales, Arizona Department of Health Services