Fox tapeworm Echinococcus multilocularis, an underestimated threat: a model for estimating risk of contact

摘要

The fox tapeworm Echinococcus multilocularis occurs across large areas of Europe, Asia and North America. In people it may cause the zoonotic infection alveolar Echinococcosis (AE). Incurable and fatal if left untreated, it therefore requires costly, intensive and lifelong medication. To ensure efficient use of resources it is crucial to know where counter-measures are most beneficial. To assist prevention efforts, we developed a model based on prevalence rates in red foxes Vulpes vulpes , fox population densities, fox defecation rates and human population densities. Our aim was to estimate and gain insight into the intensity of contamination in different environments and the relative probability of people coming into contact with tape worm eggs. Based on data from six Bavarian regions, there was a strong positive correlation (Pearson r = + 0.970, P ≤ 0.001) between human cases of AE and the relative probability of contact calculated using this model. Furthermore, the example calculations showed that due to the higher fox population density, just as much infectious material is released into the environment per day and per km2 in urban areas with low prevalence of fox tapeworms (10%) as is in rural areas with high prevalence (80%). If human population density is also taken into account, the likelihood of contact between people and infectious faeces is higher in suburban/urban than in rural areas. For example, in 2005 the likelihood of contact was 45 times higher in the city of Munich than the Bavarian average. Our model thus confirms the hypothesis of Deplazes et al. (2004 ), which emphasises the substantial risk presented to humans by fox tapeworms in suburban areas, and it calls for counter-measures.