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Serosurveillance of WNV in horses – useful tool for public health

Significant increase in outbreaks of WNV infections among humans and horses was recorded in last few years in many European countries. WNV control measures are based on detection of viral activity in particular regions and preventive control measures. Serosurveillance in sentinel animals was confirmed as a useful tool in measuring of WNV activity on particular locations and as an early warning system for general public health. In Croatia, WNV serosurveillance in horses as sentinel animals was continuously performed from 2010. The aim of this study was to analyze the WNV seroprevalence trends in horses in relation to human clinical cases in eastern Croatia. To determine the seroprevalence of WNV infection in horses, randomly selected sera samples of clinically healthy horses without vaccinal history were tested for specific IgG antibodies. Seroprevalence in five eastern Croatian counties were compared with seroprevalence in the same area in previous years. Epidemiological data about human clinical cases were collected from the official report of Croatian National Institute of Public Health. WNV seroprevalence in sentinel horses in 2010 in eastern Croatia was 5.2% with a slight increase to 6.4% in 2011. There was no evidence of human or horse clinical cases or asymptomatic acute infection in horses in these two years. During 2012 seroprevalence in sentinel horses increased significantly (10.3%) in the comparison to previous year. In this season, for the first time in Croatia, seven human clinical cases were recorded following confirmation of 12 acute infections in horses in the same part of the country. Further slight increase in horse seroprevalence (12.4%) was observed with eight acute infections of horses in a new geographical locations. No clinical infections in humans were confirmed. Seroprevalence in sentinel horses was continuously increasing in eastern Croatia from 2010 to 2013. A significant increase in viral activity among horses under serosurveillance was recorded in 2012 which in turn was an early warning for the public health in general. Based on 2012 surveillance results, intensive preventive and control measures were applied on the locations where human clinical cases, acute infection in horses or increase in seroprevalence were recorded. The highest number of WNV human clinical cases in Europe during 2013 was recorded in Serbia, bordering region to case study location. Despite high seroprevalence in sentinel horses no human clinical cases were recorded in Croatia during 2013 possible due to intensive source reduction measures based on surveillance data highlighting the importance of adequate surveillance system.

West Nile virus; Serosurveillance; Horses; Public health; Croatia

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