1. 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

2. 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.

3. 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.

4. Dengue Fever All four serotypes cause disease characterized by: Sudden onset of headache Fever Myalgia Anorexia Arthralgia

5. 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.

8. Distribution of Aedes aegypti in the United States, 2001 Positive Negative/Eradicated Intercepted Unknown Current status

9.  Study area: Tucson, Arizona-Ambos Nogales corridor. Tucson Nogales Arizona Mexico

10. 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.

13. Nogales, AZ – adjacent to border

19. 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.

20. 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.

28. 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.

29. Results of Ovi-Trapping

31. Characteristics of Study Sites

32. Temperature

33. 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.

36. VariablePositive in 2002Positive in 2003Positive Both Years Odds Ratio95% C.I.Odds Ratio95% C.I.Odds Ratio95% C.I. Minimum temp (F) 1.36*1.03-1.791.503*1.01-2.241.54*1.05-2.25 Evaporative cooling 7.61**1.68-34.52.952.55-15.918.80*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

37. 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.

38. Aedes aegypti Climate Variables Land Use Number of Breeding Sites Access to Amenities Swamp Coolers Factors in Mosquito Proliferation in the Sonoran Region Water Storage Sanitation Sewage Migration to border region Population increase Cross-border migration Minimum temperatures > 69°F Human behavior

44. 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