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APPROACHES TO STUDYING THE CLIMATE-DISEASE CONNECTION 209

FIGURE 3-7 California mosquito district risk levels 1-5 for WNV transmission: estimated from (A) temperatures downloaded from the TOPS system (inset shows the increasing duration of extrinsic incubation period with decreasing temperature and associated risk), (B) the entire risk assessment model calculated bimonthly for selected mosquito control agencies, and (C) the number of human cases within each mosquito control region of California.

FIGURE 3-7 California mosquito district risk levels 1-5 for WNV transmission: estimated from (A) temperatures downloaded from the TOPS system (inset shows the increasing duration of extrinsic incubation period with decreasing temperature and associated risk), (B) the entire risk assessment model calculated bimonthly for selected mosquito control agencies, and (C) the number of human cases within each mosquito control region of California.

mosquito control and recommendations for human personal protection provide the only methods to interrupt transmission and protect the public.

Use of forecasts and nowcasts13 for making control decisions have inherent problems, especially in California and other areas where the public (especially anti-insecticide advocates) frequently believes that the risk of applying insecticides, even in ultralow volumes (ULVs), exceeds the risk of illness or death from viral infection. Using forecasts and surveillance measures, it is possible to accurately determine that the risk of an epidemic is imminent and to apply large-scale aerial ULV adulticide treatments to immediately reduce vector abundance and transmission. In this scenario, cases are prevented, but the rationale for a large monetary expenditure and exposure of the human population appears unjustified to some because we cannot know whether the prevented cases would have occurred in the absence of vector control measures. The actions of vector control and public health officials are then questioned in the press, despite the fact that risks from pyrethrin insecticides and synergists are minimal (Peterson et al., 2005). If concurrent measures of risk are used instead of forecasts, the virus may have amplified to higher levels, some humans will have been infected before

13Forecasts or real-time measures of events in the immediate future.

210 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS

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