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.

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

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.

HCP/HCT/VBD

PAHO/WHO 2002

JRA

Reinfestation of Aedes aegypti1930s 1970 2002

HCP/HCT/VBD

PAHO/WHO 2002

JRA

Aedes aegypti:Distribution

throughout the world

Distribution of Aedes aegypti in the United States, 2001

Positive

Negative/Eradicated

Intercepted

Unknown

Current status

Study area:Tucson, Arizona-Ambos Nogales corridor.

Tucson

NogalesArizona

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 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.

% 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

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

Characteristics of Study Sites

Ecology of Study Sites

010203040506070

Nogales,MX

Nogales,AZ

Tucson,AZ

Sites

%

% irrigating aroundhouse

% evaporativecooling systems

% with > 25%vegetationcoverage*

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

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.

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

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

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

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.

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

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