Introduction

Alveolar echinococcosis is the most serious parasitic disease of humans in Europe, particularly affecting the central and eastern parts of the continent. Until the 1980s, most of the patient records were confined to a rather circumscribed area in eastern France, southern Germany, Switzerland and western Austria, and the range limit of this parasite was also thought to be restricted to this region. In the previous 20 years numerous records from foxes, and some from humans, were obtained from elsewhere in central Europe. Although the data are far from comprehensive, we assume that this parasite is distributed over most of Europe with the exception of the British Isles, Fennoscandia and the Mediterranean region.

Geographical spread and prevalence

New records have extended the known range of this parasite in Europe, although the absence of previous surveys leaves room for interpretation as to whether this reflects a range increase, or whether the parasite’s presence in these areas has formerly been unrecognized. Autochthonous occurrence of E. multilocularis was recently confirmed in the Baltic states, most of Belgium, the south and west of the Netherlands, northern Italy, eastern Austria, northern Hungary and Slovenia. Some old records exist for most countries of eastern and southeastern Europe, but no recent confirmations are available. Nevertheless, the presence of E. multilocularis in these regions is likely. On the other hand, extensive fox surveys have failed to detect infected animals in Great Britain, Norway and Finland, so these countries are either (still) non-endemic, or prevalences are at a very low level. Within the known range of E. multilocularis, prevalence increases in foxes could be demonstrated in various parts of Germany (Lower Saxony, Baden-Württemberg, Bavaria), eastern France, northern Slovakia and southern Poland (High Tatra region), and have probably occurred in many other regions in the wake of increasing fox populations. Two neozootic mammal species were added to the host list in central Europe. The raccoon dog (Nyctereutes procyonoides), a wild canid originating from eastern Asia, has shown massive population surges in Poland and eastern Germany after the extermination of rabies there, and has been confirmed as a suitable definitive host for this parasite. Feral coypu (Myocastor coypus), South American rodents with affinity to semi-aquatic habitats, were confirmed as suitable intermediate hosts in western and southern Germany. The populations of this animal are presently increasing, possibly due to climate changes, and in future this species may play some role in the transmission and dispersal of this parasite (Jenkins et al. 2005; Romig et al. 2006; Berke et al. 2008; Malczewski et al. 2008).

Transmission in urban areas

In many cities and towns of central Europe (France, Switzerland, Germany, the Czech Republic and Austria), ‘urban foxes’ have become established. They form self-sustaining subpopulations, showing only limited exchange with the surrounding populations of rural areas. Due to the constant availability of food, home ranges of individual foxes tend to be small and population densities can be far higher than in rural areas, still showing a tendency to increase. Prevalences of E. multilocularis in these populations vary from town to town. They may reach levels of >40% e.g. in Zurich and Geneva, but, as a rule, are lower than in surrounding rural habitats, as rodent intermediate hosts are less frequently available as part of fox diet in areas of human settlement. However, fox-human contact is more intense in towns, and there is concern about an increasing danger of infection. The most critical areas seem to the peripheries of cities and towns, where both foxes and the rodent intermediate hosts occur at high densities (Deplazes et al. 2004; Robardet et al. 2008).

Human infection

Alveolar echinococcosis is still a rare disease, with prevalences in the range of 0 – 150/100,000. However, a recent data evaluation in Switzerland showed a more than twofold increase of annual incidence between the periods 1993–2000 and 2001–2005, from 0.10/100,000 to 0.26/100,000. Official surveillance data in Germany, which indicated approximately 20 newly diagnosed cases of this reportable disease in the country annually, were shown to be inaccurate: a comparison of various data sources showed that the official surveillance missed 67% of cases. Although the majority of human cases still cluster in the ‘old’ endemicity areas of southern central Europe, new cases have sporadically appeared in recent years in areas which were previously thought to be non-endemic, e.g. northern Germany. Despite the establishment of the parasite in urban areas, the risk for alveolar echinococcosis (in Germany) is still associated with a rural lifestyle (Kern et al. 2004; Schweiger et al. 2007; Berke et al. 2008; Jorgensen et al. 2008).

Control trials

There are few options for control of E. multilocularis. Vaccines for humans or animals will not be available in the foreseeable future. The reduction or extermination of host animals, e.g. foxes, is either impractical, unethical or ineffective. Therefore, anthelmintic treatment of foxes, applied via baits, has been evaluated in different regions and under different local conditions. No standardized approach is available as yet, but several large-scale trials have been performed in northeastern and southwestern Germany in areas of >3000 km2. Monthly to three-monthly distribution of baits (containing 50 mg praziquantel each, distributed at densities of 20/km2 by aircraft) has led to drastic reductions in the prevalence of E. multilocularis prevalence over time both in high and low endemicity areas, but did not achieve local eradication. In a different approach, small scale distribution of baits (by hand) at higher densities (50/km2) in the City of Zurich, Switzerland, has shown an encouraging effect in areas as small as 1 km2. Interestingly, a long-term effect was noted: three years after the last bait distribution, an extremely low prevalence was still observed in an area that had been baited monthly for almost four years. In the course of an ongoing trial in Bavaria, Germany, where both approaches are combined, prevalence rates could also be reduced to close to the detection threshold in a 200 km2 area.. However, the cost of these approaches is not trivial, and large or small scale application is not indicated without long-term financial and political commitment. Further evaluation and optimization of the baiting protocols are necessary. Due to the expense and time necessary for field trials, modelling studies will gain increasing importance for this purpose (Hansen et al. 2003; Ito et al. 2003; Romig et al. 2007; Hegglin and Deplazes 2008 König et al. 2008).