Vector control strategies and practices against West Nile virus management

Authors: CHASKOPOULOU, ALEXANDRA - European Biological Control Laboratory (EBCL); BRAKS, MARIETA - National Institute For Public Health And The Environment (RIVM); VAN BORTEL, WIM - National Institute For Public Health And The Environment (RIVM)

Submitted to: Technical Report
Publication Type: Other
Publication Acceptance Date: 10/1/2020
Publication Date: 11/1/2020
Citation: Chaskopoulou, A., Braks, M., Van Bortel, W. 2020. Vector control strategies and practices against West Nile virus management. Technical Report.

Interpretive Summary: West Nile virus (WNV) infection represents a serious burden to human and animal health worldwide because of the capacity of the virus to disperse fast and adapt to a large variety of environments causing unforeseen and large epidemics. In the absence of effective vaccination, vector control remains the primary, and perhaps the only, line of defense in preventing and containing West Nile virus outbreaks. An effective vector control strategy utilizes the appropriate combination of vector control tools (every tool has its limitations by default and to help balance these limitations a synergy of methods is often required), under a specific operational context, to reduce and keep vector populations below thresholds where WNV transmission to humans is infrequent. Those thresholds are region specific and are a product of long-term collection and analysis of integrated surveillance data sets (environmental indicators, entomological indicators, veterinary indicators, epidemiological indicators). With this report we aimed to collate information on WNV vector management experiences across the world under specific operational context and identify gaps in knowledge and capacities relating to effective WNV vector management practices.

Technical Abstract: West Nile virus (WNV) infection represents a serious burden to human and animal health worldwide because of the capacity of the virus to disperse fast and adapt to a large variety of environments causing unforeseen and large epidemics. WNV invaded the United States (US) in 1999 and within 4 years spread rapidly across the country despite the intensive and expanded organized vector control efforts to prevent invasion. A total of 51.747 WNV human cases and 2.381 deaths (as of January 2020) have been recorded since the introduction of the virus which is currently considered the leading cause of mosquito borne disease in the continental US. Significant research efforts have been dedicated on deciphering the complex ecology of the virus in order to better predict and contain outbreaks, while significant improvements in vector surveillance and control programs have been made across the country. However, the uneven distribution of sufficient surveillance and control capacities (leaving gaps in preparedness and response), the inconsistent vector surveillance activities, and, delays to act upon surveillance indicators effectively, have been identified as the primary factors hindering WNV abatement in the United States. In Europe the virus was detected for the first time in 1958 in Albania and was sporadically recorded until 1996, when a major outbreak of infection characterized by a high fatality rate (10%) occurred in Romania with 393 confirmed cases. Since then there has been a continuous increase and spread of WNV reported cases in humans and horses across Europe, which was attributed, partly, to the improved surveillance and diagnostic capacities but, also, to the introduction and establishment of WNV lineage 2 strains responsible for major outbreaks in Central European and Eastern Mediterranean countries, such as Greece, Italy, Austria, Hungary and Serbia. An extraordinary increase of WNV human cases across many EU/EEA and EU neighboring countries was observed in 2018 with the total number of human infections (n=2083) exceeding by far the total number from the previous 7 years (n=1832). Furthermore, the distribution of the virus expanded northwards with the first equine outbreak reported in Germany in 2018, followed by autochthonous human cases in 2019. This unprecedented rise of disease incidence in combination with the rapidly growing geographic expansion of the virus indicates that capacities to address and contain this threat are urgently needed across Europe. European national and local public health agencies are on the front lines of defense against mosquito-borne disease, however, very little information is available on whether or not they have the knowledge & operational capacity to prepare for and respond to a WNV outbreak. National and regional WNV surveillance and response plans are already in place in some countries with a variety of WNV risk mitigation strategies and vector control interventions but with little common understanding on their effectiveness and no EU-wide strategy and technical guidance to properly apply these methods and assess/evaluate their efficacy. There is a plethora of laboratory-based and small-scale field studies demonstrating impact of vector control methods on the abundance of WNV vectors. On the other hand, controlled, large-scale, operational studies assessing the impact of control methods against vector abundance while making the link between entomological efficacy and epidemiological impact are scarce and the vast majority of those studies were conducted in the US. To help address these gaps we conducted a survey for updating information on the current WNV surveillance and control capacities across European countries. Through this survey we aimed to identify and evaluate the operational challenges each country is facing in implementing vector control and to prioritize the needs