2012 Abundance Avg Abundance Abundance

Transcription

1 Date of Report: 1/3/217 NORTH SHORE MOSQUITO ABATEMENT DISTRICT 217 Surveillance Summary West Nile Virus Surveillance NSMAD maintains CDC gravid traps placed at 19 locations throughout the District to sample mosquitoes responsible for transmitting West Nile Virus (WNV). Mosquitoes are collected 24 hours a day, seven days a week and are identified; counted to estimate relative abundance; and Culex pipiens mosquitoes are tested in batches of up to 6 specimens using the RAMP WNV assay to estimate WNV infection rate. Collections for WNV surveillance started May 22, 217 (week 21). In the graphs below, 217 surveillance results are shown as the red line, results obtained during 212 (the most recent WNV outbreak year with 2 human cases in the District) are shown in the blue area, results obtained between 21 and 216 (excluding 212) represent nonoutbreak years (-4 cases per year) and are shown in the tan area. Vector Species Abundance: Cx. pipiens abundance in gravid traps was near the higher end of the nonoutbreak-year levels for most of the 217 season. There was an increase in abundance at the end of September (weeks 38-39). WNV surveillance ended Sept. 29, 217. Number collected per trap night Abundance Avg Abundance Abundance

2 WNV Infection Rate: WNV infection in Cx. pipiens (shown in the graph below as the Maximum Likelihood Estimate of the Infection Rate per 1 mosquitoes) was first detected during week 22. At that point the infection rate was 2/1. Infected mosquitoes were consistently found somewhere in the District during every subsequent week of the surveillance season, and by week 31 WNV-infected mosquitoes had been found in each of the 14 towns within NSMAD. The infection rate stayed at relatively low levels from week 22 through week 27, then increased rapidly and reached moderately high levels of 18-23/1, which lasted for approximately 6 week through week 35. Infection rates during that period were considerably above the non-outbreak-year levels. By week 36, the infection rate had decreased to low levels which continued to decline through the remainder of the season Infection Rate Avg Infection Rate (21-216) 217 Infection Rate 5 Infection Rate (#/1)

3 WNV Vector Index: The Vector Index combines the Cx. pipiens abundance and infection rate data to produce an estimate of the number of number of WNV infected mosquitoes in the area. This index is associated with human risk of WNV infection and helps us identify locations and time periods when risk increases. In the NSMAD surveillance program, a vector index >1 occurring early in the season is associated with increased risk of multiple human WNV cases. During 217, the Vector Index exceeded 1. at week 3 and remained at above average levels through week Vector Index Avg Vector Index (21-16) 217 Vector Index Vector Index WNV Surveillance Summary: West Nile virus activity in 217 was higher than the average level observed during non-outbreak years from week 27 through week 33. Though WNV activity increased earlier in 217 than in other non-outbreak years, the risk levels did not reach the levels seen in 212. Also, the peak of WNV activity in 217 occurred several weeks later than during 212. As of the date of this report, the Illinois Department of Public Health is reporting 78 human WNV cases have occurred statewide, 42 of which are from Cook County. Of the human cases reported in Cook County, two are from communities served by the NSMAD. Symptom onsets of the two cases in the NSMAD occurred during week 35. WNV testing summary: During 217, a total of 71,121 mosquitoes were tested in 1,565 batches. Of these, 553 batches were positive for evidence of WNV using the RAMP assay. Batches Tested Season Total Municipality # WNV+ # Tested Evanston Glencoe 6 47 Glenview/Golf Kenilworth 41 1 Lincolnwood Morton Grove 36 8 Niles 6 52 Northbrook Northfield 2 61 Skokie Wilmette Winnetka 8 52 Total

4 Nuisance Mosquito Surveillance New Jersey Light Traps are placed in nine locations throughout the district to sample biting adult mosquitoes that affect quality of life. Specimens are collected four nights per week, identified and counted to provide an estimate of the biting mosquito abundance in the district. This information is used to determine pest mosquito levels and plan larval and adult control activities. The graph below shows the average number of mosquitoes (all species) collected per trap night, per week in the blue area while the red line indicates the number collected during 217. Peaks in the long-term average graph are generally the result of heavy rains producing a very large emergence of floodwater mosquitoes during a single year. In general, biting mosquitoes become very noticeable to residents when the abundance reaches 2-3/trap night. During 217, sampling using NJLTs began in mid-may (week 21). Relatively normal rainfall patterns during the early part of the season produced a gradual increase in biting mosquitoes through late June and early July. A single, very heavy rainfall event in late July produced the large population of nuisance mosquitoes observed during late July and early August. Dry weather at the end of the summer reduced floodwater mosquito production. New Jersey Light Trap Collections Average number collected/trap night/week Average

5 Aedes albopictus in NSMAD Late in the 216 season, a small population of Ae. albopictus was found in a neighborhood in the northeast portion of Skokie. A total of only 64 Ae. albopictus was collected in 216, suggesting that this was a relatively low abundance population. Based on this finding, NSMAD placed BG Sentinel traps throughout the same neighborhood during the 217 season. Two adult Ae. albopictus mosquitoes were collected in early July (week 27). No additional Ae. albopictus adults were collected in our traps for the remainder of the 217 season. 5

6 Weather Monitoring The graph below shows the weekly precipitation and average temperature for the 217 season from January through October. Temperature and rainfall patterns were relatively normal in the spring. There was an abrupt increase in average temperature in late May, with relatively high temperatures persisting through mid-august. June and early July were relatively dry. A heavy rainfall event in late July was followed by another dry period. The heavy rainfall events were associated with a large emergence of floodwater mosquitoes across the district. The hot dry periods were associated with increases in Culex pipiens abundance and increases in WNV infection rate. 216 Average Temperature and Precipitation Temperature ( F) Precipitation Average Temperature Jan Feb Mar Apr Month and Week Precipitation (Inches) Source: NOAA Station: Chicago Botanical Garden, IL US GHCND:USC Cumulative degree days provide information about accumulation of thermal energy that is associated with shorter generation time (and more rapid growth) in mosquito populations and more rapid virus replication in virus-infected mosquitoes. The graph below shows that for much of the mosquito season, 217 (solid red line) was average to below average and much lower than in 212, which had the most rapid increase and highest level of cumulative degree days since 21 and was the last WNV outbreak year in which 2 human WNV cases occurred in NSMAD. Cumulative Degree Days (above 6 F) Degree Days (6 F)

7 The graph below shows cumulative precipitation levels, and indicates that until late June, 217 was a relatively average year for precipitation (solid red line). There was a rapid increase in cumulative precipitation through July, which moved 217 nearer the levels seen in some of our wettest years. This was followed by a relatively dry spell at the end of the season. In contrast, precipitation during the 212 outbreak year (orange dashed line) was the lowest for cumulative precipitation since 21. Cumulative Precipitation Cumulative Precipitation (inches) Month Dave Zazra Communications Manager dzazra@nsmad.com 7