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Entomologic studies after a St. Louis encephalitis epidemic in Grand Junction, Colorado
T F Tasi1, G C Smith, M Ndukwu
1Division of Vector-Borne Viral Diseases, Centers for Disease Control, Fort Collins, CO 80522.
American Journal of Epidemiology
|August 1, 1988
Summary
St. Louis encephalitis virus was found in two mosquito species, Culex tarsalis and Culex pipiens pipiens, in Grand Junction, Colorado. Gravid traps revealed Cx. p. pipiens as the primary vector, with higher infection rates in Cx. tarsalis.
Area of Science:
- Arbovirology
- Medical Entomology
- Epidemiology
Background:
- A St. Louis encephalitis (SLE) epidemic occurred in Grand Junction, Colorado, in 1985.
- Vector mosquito surveillance was conducted in 1986 to understand SLE transmission dynamics.
Purpose of the Study:
- To correlate mosquito bionomics and infection rates with human disease occurrence.
- To identify the primary vector species and their role in SLE transmission.
Main Methods:
- Mosquitoes were collected using gravid traps and Centers for Disease Control (CDC) light traps.
- Surveillance was conducted from June to September.
Main Results:
- St. Louis encephalitis virus was detected in Culex tarsalis and Culex pipiens pipiens.
- Culex p. pipiens was the predominant mosquito collected, primarily in gravid traps.
- Cx. p. pipiens populations emerged later but persisted longer than Cx. tarsalis populations.
- While Cx. tarsalis had higher infection rates, increased Cx. p. pipiens numbers in late summer led to more infected Cx. p. pipiens.
- Gravid traps were more effective than light traps alone for detecting Cx. p. pipiens' role.
Conclusions:
- Culex p. pipiens plays a significant role in SLE transmission, potentially underestimated in previous studies using only light traps.
- Urban SLE cycles associated with Cx. p. pipiens and rural cycles associated with Cx. tarsalis may coexist in the Western United States.