Impact of West Nile Virus Outbreak Upon St. Tammany Parish Mosquito Abatement District

Abstract

St. Tammany Parish, Louisiana, experienced an outbreak of West Nile virus (WNV) in 2002, with 40 human cases and 4 deaths, most occurring from June to August. Culex pipiens quinquefasciatus was believed to be the primary vector of WNV during the outbreak, although circumstantial evidence suggests that Aedes albopictus also may have been involved in transmission. Dead bird reports were the 1st indication of the outbreak and were an excellent indicator of WNV activity; however, sentinel chickens were the most effective in tracking viral activity. Although sentinel chickens tested positive 2-3 wk after the 1st dead bird, they peaked at about the same time as human cases, and continued testing positive when viral activity was no longer detected in birds and mosquito pools. Lag time between the 1st positive sentinel chicken and the peak in human cases was 6 wk. If this trend continues in the future, sentinel chickens could be used to predict the peak in number of human cases. The 2002 WNV outbreak had a strong impact on operational budget of the St. Tammany Parish Mosquito Abatement District (88% increase above the 3-year average). Vector control activities accounted for most of the operational increase and consisted of targeted population reduction of known WNV-competent mosquito species. The goal of these activities was to prevent new human WNV cases. The 3- to 10-fold reduction in vector mosquito populations from May to August, together with a dramatic drop in number of new human cases by the end of August, indicated that our strategy was effective.

Ecology of Potential West Nile Virus Vectors in Southeastern Louisiana: Enzootic Transmission in the Relative Absence of Culex quinquefasciatus

“…However, 2002 was an epidemic year, and WNV disease case numbers dropped sharply after July. 18 The STPMAD did not detect positive Cx. quinquefasciatus pools after July, 18 and a separate investigation conducted from August 3 to 15 19 did not detect viruspositive mosquito pools after August 10.…”

“…pipiens complex, plays a role in WNV transmission analogous to the role of Cx. pipiens in the north 18,19,29,30 and Cx. pipiensquinquefasciatus hybrids in the middle latitudes of the United Figure 4.…”

“…salinarius as a possible secondary vector. 18,19 Similarly, in East Baton Rouge Parish (EBRP),~100 km west of St. Tammany Parish, Cx. quinquefasciatus is the species most frequently found infected with WNV.…”

“…Forty cases with four deaths were recorded, with most cases occurring between June and early August. 18 Entomologic surveys conducted during this outbreak incriminated Cx. quinquefasciatus as the main vector, with Cx.…”

“…To sample mosquitoes in the canopy as well as at ground level, two dry ice-baited Centers for Disease Control and Prevention (CDC) miniature light traps were placed at each site, with one trap at 1.5 m (down trap) and one trap at 6 m above the ground (up trap). One gravid trap baited with a fish oil emulsion (Alaska Fish Fertilizer, Alaska Fish Fertilizer Co., Renton, WA; 59 mL in 6.8 L tap water and incubated for 3 days at ambient outdoor temperature) 18 was also placed at each site to sample Cx. quinquefasciatus.…”