The Cu/ex surveillance activities focus primarily on the abundance and seasonality of the vector species. Vector surveillance is also implemented to assess mosquito infection rates and as a xenomonitoring tool (Table). The main objectives of the surveillance are outbreak investigations and assessment of the level, place or time of transmission risk (Table).
Table 3. Indicators assessed by the Culex surveillance activities (multiple answers possible) (n = 17)
| Indicator | Number of countries |
|---|---|
| Mosquito presence/absence | 11 |
| Mosquito abundance | 13 |
| Mosquito seasonality | 12 |
| Mosquito infection rate and xenomonitoring | 13 |
| Mosquito behavioural traits | 3 |
| Insecticide/biocide resistance | 2 |
| Don't know / NA | 1 |
| Other | 1 |
Table 4. The objectives of the Culex surveillance (multiple answers possible) (n = 17)
| Objective | Number of countries |
|---|---|
| Assessment of level, place and/or time of transmission risk | 10 |
| Assessment of nuisance levels | 5 |
| Investigation of outbreaks | 12 |
| Assess quality/efficiency of mosquito control intervention | 6 |
| Don't know / NA | 2 |
| Other | 1 |
For the two most important objectives, i.e. assessment of level, place or time of transmission risk, and investigation of outbreaks, active surveillance is the primary type of surveillance. Depending on the objective, surveillance is implemented country-wide or in certain parts of the country. The reasons for the implementation of surveillance in certain parts of the country only are linked with the risk of WNV being restricted to those parts, the lack of resources to implement surveillance country-wide, linked to the actual organisation of the surveillance which is, in certain countries, regionally based, and the fact that Cu/ex surveillance in certain countries is linked to Aedes invasive mosquito surveillance.
The funding for active surveillance related to most of the objectives, is limited in time. Funding of the active surveillance activities related to outbreak investigation, in seven out of 17 countries, is embedded in a long term (> 3 yr) strategy of disease risk assessment and control. Likewise, passive surveillance, in most of the countries which answered this question, is time-limited funding. Reporting of the surveillance indicators is voluntary in most countries, except for surveillance activities related to outbreak investigations (Table).
Table 5. Is reporting of the surveillance indicators voluntary or compulsory?
| Objective | Compulsory | Voluntary | Don't know/NA |
|---|---|---|---|
| Prevention of establishment after introduction of exotic mosquito species | 3 | 5 | 9 |
| Assessment of level, place and/or time of transmission risk | 5 | 7 | 5 |
| Assessment of nuisance levels | 0 | 8 | 9 |
| Investigation of outbreaks | 9 | 6 | 2 |
| Assess quality/efficiency of mosquito control intervention | 0 | 7 | 10 |
Six of the 12 countries implementing Culex control use preventive control to reduce disease risk or nuisance. Eleven countries deploy reactive control after detection of cases to control an outbreak. One country (Hungary) stressed the fact that control is implemented primarily to decrease biting nuisance and one country (Greece) implements reactive control, in addition to after the detection of human cases and after the detection of WNV positive mosquito pools (Culex pipiens) or WNV positive animals.