He conquered Persia, Greece and Babylon and was revered and feared in East and West alike. At the age of 32, in the height of his power and glory, he was brought down... by a mosquito. According to recent speculations, Alexander the Great may have died as a result of infection by West Nile virus [1
West Nile virus (WNV) infections may have been occurring in the Middle East for centuries. The virus has spread to new areas of the world and to new populations, causing infections that are characterized by signs and symptoms. Detected in North America for the first time in 1999 in the state of New York, it has since spread throughout the continent. Three years later, in 2002, the number of human cases of infection by this virus had increased dramatically. In the United States, 4156 cases and 284 deaths were confirmed. Moreover, 9862 confirmed cases (with 264 deaths) were reported in 2003 and 2470 (with 88 deaths) in 2004 (as of January 11th
, 2005) [2
The WNV was detected in mosquitoes, Corvidae
(American Crows, Blue Jays and Common Ravens in our context) and humans for the first time in the province of Quebec, Canada, in early summer of 2002. A total of 20 confirmed human cases (including 3 deaths) were reported in 2002, 17 confirmed cases in 2003 (no deaths) and 3 cases in 2004 (1 death). This situation forced the Government of Quebec to adopt, in 2003, a public health protection plan against the virus [3
] that remains in place to date. The main objectives of this plan are: to prevent complications and human deaths related to WNV infections, to ensure the early detection of the presence of the virus in a geographic area, to identify areas of potential transmission to humans for preventive action and monitoring, and to qualify the level of transmission to humans. The plan comprises several areas of intervention and their performance criteria:
- Monitoring: an integrated monitoring system (human, ornithological, entomological) in real-time;
- Laboratory: speed and provincial autonomy with regards to diagnosis (human, ornithological, entomological);
- Information: a communication plan;
- Intervention: rapid, effective, and flexible to adjust to the evolution of the epidemiologic situation;
- Research and evaluation: of the effectiveness and impacts of the actions taken;
- Decision process: a public health structure to optimize intervention capacity.
Given the particular epidemiologic character of the infection (avian amplifiers, transmission by mosquito vectors), the monitoring component of the plan is comprised of three interrelated elements:
- The monitoring of human cases of infection: the presence of infected persons that have acquired the infection locally confirms an active transmission of the WNV in the concerned area;
- The monitoring of animals: the presence of clustered dead Corvidae infected by the WNV indicates a potential source of amplification; these observations help identify target sites for mosquito monitoring;
- The monitoring of mosquitoes: the presence of a pool of infected mosquitoes indicates that a WNV source exists that presents a potential for the transmission of WNV to humans.
Analysis of the monitoring data makes it possible to target preventive interventions such that the appropriate personal, community, and environmental protection interventions can be considered; however, to be useful, the monitoring data must be available in real-time. The development of an information system to support the monitoring component of the intervention plan for the province of Quebec was entrusted to the Institut national de santé publique du Québec (INSPQ) in 2003 by the Ministère de la Santé et des Services sociaux (MSSS). The mandate of the INSPQ includes the implementation and continual update of an extranet web site dedicated to online data entry, data warehousing and document exchange. Moreover, this site included tables or graphs of relevant surveillance data, an online tool ensuring the validation and geographic localization of relevant events and an online real-time mapping tool for the integration of all data. The INSPQ thus developed the Integrated System for Public Health Monitoring of West Nile Virus (ISPHM-WNV) that allows the different actors involved to rapidly and easily assess the situation and recommend adapted interventions.
Using this system, the evaluation of the epidemiologic situation is carried out by an Expert Group that includes representatives of the appropriate government departments, scientists, and regional health authorities, in order to recommend the optimal interventions against WNV. In the event of a major epidemic situation, a high-level Advisory Committee is consulted on interventions before the Deputy Minister makes a decision.
In Canada, several provincial surveillance systems that include a WNV monitoring component have been implemented in the last few years, and information is shared through the Canadian Network for Public Health Intelligence (CNPHI). The CNPHI is targeted at improving the capacity of the Canadian health system to reduce human illness associated with infectious disease events by supporting intelligence exchange, surveillance activities and outbreak investigations. It is a national framework to collect and process surveillance data, disseminate strategic intelligence, and coordinate response to biological threats [4
]. It comprises the West Nile virus Monitor, a surveillance component fed with provincial monitoring data that allows the visualisation of maps and tables. The provinces are responsible for the monitoring of the virus on their respective territory and the implementation of programs and systems to support this task. For example, the British Columbia Centre for Disease Control has implemented the Internet Geographic Information System (GIS) that allows the interactive mapping of various monitoring data related to WNV [5
]. In the United States, the Centers for Disease Control and Prevention (CDC) have implemented the National WNV Surveillance System [6
]. The objectives of the system are to monitor the geographic and temporal spread of WNV, develop national public health strategies for WNV surveillance, prevention, and control, develop a more complete regional picture of the geographic distribution and incidence of the other clinically important arboviruses, and provide national and regional information to public health officials, elected government officials, and the public. The data entry is done by reporting jurisdictions at the state level through the ArboNET system, the national electronic surveillance system established by CDC to assist states in tracking WNV and other mosquito-borne viruses. The system includes a mapping component and the maps it produces are available on the United States Geological Survey (USGS) web site. On a state or local level, WNV monitoring programs and infrastructures have been implemented. For example, see [7
] for information on the infrastructure implemented by the State of New-York. The City of New York has also implemented the Dynamic Continuous-Area Space-Time (DYCAST) GIS system that was developed to identify and prospectively monitor high-risk areas for WNV [8
In line with those previous examples, this paper outlines the context, architecture and different capabilities of the ISPHM-WNV, including its spatial and cartographic functionalities. In addition, examples of its utility as a tool for the management of risks and the reporting of results on a daily basis are presented. Finally, the paper explores future considerations for the development of such systems.