Transcript The Potential for the Emergence of Dengue Fever along the

The Potential for the Emergence of Dengue
Fever in the S.W. United States along the
International Border
Mary Hayden, Ph.D.
University of Colorado
July 23, 2004
NISSC
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.
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.
Dengue Fever
 All four serotypes cause disease
characterized by:
 Sudden onset of headache
 Fever
 Myalgia
 Anorexia
 Arthralgia
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.
A
HCP/HCT/VBD
Reinfestation of Aedes aegypti
1930s
PAHO/WHO
2002
1970
2002
HCP/H
Aedes aegypti:
Distribution
throughout the world
PAHO/WHO
2002
Distribution of Aedes aegypti in the United States, 2001
Current status
Positive
Negative/Eradicated
Intercepted
Unknown
 Study area:
Tucson, Arizona-Ambos Nogales corridor.
Tucson
Nogales
Arizona
Mexico
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.
Nogales, AZ – adjacent to border
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.
Measures
 Current satellite imagery has been examined to determine land
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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.
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.
Results of Ovi-Trapping
% Positive Traps by Site
120
100
2002 positives
Percent
80
2003 positives
60
% pos. in yr. 2 also
pos. in yr 1
40
20
0
Nogales, MX Nogales, AZ Tucson, AZ
Sites
Number of Positive Sites by Month, 2002 & 2003
Number of Sites
60
50
40
30
20
10
0
June
July
August
2002
2003
September
Characteristics of Study Sites
%
Ecology of Study Sites
70
60
50
40
30
20
10
0
% irrigating aro und
ho use
% evapo rative
co o ling systems
% with > 25%
vegetatio n
co verage*
Nogales, Nogales, Tucson,
MX
AZ
AZ
Sites
Temperature
120
Temp (F)
100
80
Nogales, MX
60
Nogales, AZ
40
Tucson, AZ
20
0
2002
2003
2002
2003
Minimum
Maximum
Temperature (F) Temperature (F)
Results: Differences Between Sites
 Socioeconomic differences between Mexico and U.S.
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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.
12
10
8
6
4
2
0
15.00
10.00
5.00
0.00
60-65.4
65.4-68.4 68.4-69.9 69.9-71.5
71.5-75
Tem perature (F)
Pos Sites
Square Root of Eggs
No. of Positive
Sites
Square Root of
Egg Count
Eggs and Positive Sites by Minimum
Temperature, 2002-2003
Number of Sites
Number of Positive Sites by Presence of
Swamp Coolers
30
25
20
15
10
5
0
Both Years
Year One
Period of Data Collection
Yes
No
Year Tw o
Presence/absence of Swamp Cooler, Average
Minimum Temperature Predict Presence of
the Mosquito
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*
1.6148.25
Controlling for humidity, location of site, and maximum temperature.
Conclusions
 Ae. aegypti is well-established in this region, suggesting the
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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.
Factors in Mosquito Proliferation
in the Sonoran Region
Climate
Variables
Number
of Breeding
Sites
Minimum
temperatures > 69°F
Water
Storage
Aedes
aegypti
Swamp
Coolers
Migration
to border
region
Sanitation
Sewage
Land
Use
Human behavior
Population
increase
Access to
Amenities
Cross-border
migration
Collaborators
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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