Update on assessment of risk of introduction of Echinococcus multilocularis to mainland Norway

Abstract

Background. The VKM Panel on Biological Hazards has updated the Scientific Opinion regarding introduction and establishment of the parasite Echinococcus multilocularis (EM) in mainland Norway. The previous risk assessment was published in 2012 and is, therefore, in need of updating, as the situation may have changed, and new information has become available. Methods. Data was collected through a literature search and examination of published surveillance reports, providing an update on existing literature on monitoring for introduction of EM into mainland Norway, the spread of EM, particularly in Sweden,and contamination of imported fresh produce with EM. The effects of different control measures, as described in the literature, were also investigated. The feasibility and advantages of adopting a more quantitative approach to assess the spread of EM in Norway were also evaluated. Results. A decade after its first identification in Sweden in 2011, the prevalence of EM in the country is still low, with a limited distribution. This indicates a slow rate of spread, with no indications that the parasite has spread closer to the border with Norway. EM has not been detected in mainland Norway and analysis of imported fresh produce has not detected EM DNA. Control measures, such as mandatory treatment of dogs entering Norway with appropriate anthelminthics (containing praziqunantel) are in place. However, the extent to which treatment compliance is checked and enforced at land and maritime borders is not documented. The possibility for modelling was explored and quantitative methods, like general episystems modelling (GEpMs), were identified as potentially relevant. Conclusion. Conclusions reached in the previous Scientific Opinion were valid at that time and remain valid now for EM in Norway. Infected dogs can introduce the parasite, and even a single infected dog may result in local establishment. This depends on various factors, such as whether suitable rodent hosts, and subsequently foxes preying on those rodents, occur locally and are exposed and susceptible. Spread of EM from Sweden to Norway by foxes is likely a question of time. Estimation of introduction-time distribution is, however, currently impossible. Increased border controls, to ensure dogs entering Norway have been suitably treated to eliminate the parasite, and, potentially, risk-dependent surveillance of foxes in areas bordering Sweden are identified as preventative measures. In addition, use of deworming bait, rather than culling of foxes, in areas where parasite is detected, could be important aspects of EM control in wildlife should the parasite be introduced. Uncertainties and data gaps. The main uncertainties are linked to the limited size of the Swedish outbreak and thus the data available from Sweden, the lack of information regarding the number of dogs entering Norway untreated, and the nature of sampling and surveillance in Norway. This means there is a substantial risk for introductions of EM to Norway becoming established in wildlife before they are detected by surveillance.