Use of Scented Sugar Bait Stations to Track Mosquito-Borne Arbovirus Transmission in California

Abstract

Laboratory and field research was conducted to determine if Culex tarsalis Coquillett expectorated West Nile virus (WNV) during sugar feeding and if a lure or bait station could be developed to exploit this behavior for WNV surveillance. Experimentally infected Cx. tarsalis repeatedly expectorated WNV onto filter paper strips and into vials with wicks containing sucrose that was readily detectable by a quantitative reverse transcriptase-polymerase chain reaction assay. Few females (33%, n = 27) became infected by imbibing sugar solutions spiked with high concentrations (10 7 plaque forming units/ml) of WNV, indicating sugar feeding stations probably would not be a source of WNV infection. In nature, sugar bait stations scented with the floral attractant phenyl acetaldehyde tracked WNV transmission activity in desert but not urban or agricultural landscapes in California. When deployed in areas of the Coachella Valley with WNV activity during the summer of 2011, 27 of 400 weekly sugar samples (6.8%) tested positive for WNV RNA by reverse transcriptase-polymerase chain reaction. Prevalence of positives varied spatially, but positive sugar stations were detected before concurrent surveillance measures of infection (mosquito pools) or transmission (sentinel chicken seroconversions). In contrast, sugar bait stations deployed in urban settings in Los Angeles or agricultural habits near Bakersfield in Kern County supporting WNV activity produced 1 of 90 and 0 of 60 positive weekly sugar samples, respectively. These results with sugar bait stations will require additional research to enhance bait attractancy and to understand the relationship between positive sugar stations and standard metrics of arbovirus surveillance. Keywordssurveillance; West Nile virus; sugar feeding; bait station; Culex tarsalisIn North America the mosquito-borne encephalitides, including West Nile virus (WNV), are maintained and amplified in enzootic transmission cycles involving vector mosquitoes and a variety of passeriform birds (Komar 2003, Kramer et al. 2008. Surveillance programs track the intensity of enzootic amplification to provide antecedent measures of risk useful in implementing timely intervention to prevent tangential transmission to humans and equines that may suffer neuroinvasive disease and death. Testing groups of mosquitoes (pools) for the presence of virus provides an estimate of infection incidence but not transmission, although virus titer in positive pools may be linked to transmission potential (Armstrong and Andreadis 2010). To monitor the intensity of transmission, groups of sentinel animals such as chickens, are deployed at strategic sites and monitored over time for evidence of infection. However, the bulky nature of chicken coops and the cost of maintenance typically Recently, FTA cards (Whatman International Ltd., Maidstone, United Kingdom) impregnated with honey were used to measure Barmah Forest and Ross River virus transmission by host-seeking mosquitoes collected using traps baited with CO 2 gas (HallMe...