A stochastic model of Echinococcus multilocularis transmission in Hokkaido, Japan, focusing on the infection process

Abstract

Echinococcus multilocularis causes human alveolar echinococcus. In Japan, high prevalence of E. multilocularis among the fox population has been reported throughout Hokkaido. Accordingly, control measures, such as fox hunting and the distribution of bait containing Praziquantel, have been conducted. This study developed a transmission model for individuals in the fox population and included a stochastic infection process to assess the prevalence of E. multilocularis. To make our model realistic, we used the worm burden for each individual in the fox population. We assumed that the worm burden depends on the number of protoscoleces in a predated vole and the number of infection experiences. We carried out stochastic simulations with 1000 trials for the situations of Koshimizu and Sapporo, Hokkaido, Japan. The distribution of the worm burden among foxes obtained using the model agreed with dissection data. The simulation indicates that a careful choice of season is necessary for an effective distribution of Praziquantel-containing bait.A stochastic model for E. multilocularis, which can assess the range of the prevalence in the fox population, would be helpful in analyzing their complex life-cycle and also in designing control strategies.

Dynamics of the Force of Infection: Insights from Echinococcus multilocularis Infection in Foxes

“…A decreased cost of baiting foxes increases the cost benefit as a similar reduction in the numbers of human AE cases would be expected to be achieved as earlier suggested [15] based on epidemiological data [23], [24]. Theoretical models [40], [41], have also suggested seasonal transmission of E. multilocularis in Japan. However, our model is also challenged with field data, where as the conclusions of previous models are based on simulations.…”

Synthesising 30 Years of Mathematical Modelling of Echinococcus Transmission

“…an exposed but not yet infectious class, also referred to as an ‘E’ class). This ‘latent’ class was present in four of the eight E. multilocularis models for both definitive and intermediate hosts [13], [18], [26], [27]. Inclusion of a ‘latent’ class, however, does not always contribute qualitatively to the dynamics of a model [25].…”

“…However, this is dependent on the level of endemicity as classic age-prevalence curves of E. granulosus indicate that very young dogs may not survive long enough to become infectious [35]. The inclusion of an age structure in the definitive (fox) host when modelling E. multilocularis occurred as a result of field data showing higher worm burdens in juvenile foxes compared with adult foxes in Hokkaido, Japan [27] and is also thought to allow the model to more realistically reflect population dynamics by assigning different death rates to hosts of varying age [17], [27].…”

“…Two E. multilocularis models from Japan therefore accounted for seasonally dynamic host populations because the primary definitive host, the red fox ( Vulpes vulpes ), and intermediate host, the grey-sided vole ( Clethrionomys rufocanus ), showed marked seasonal variations in population size [17], [27]. However, it is argued by others that introducing seasonally dynamic host populations would add unnecessary complexity and provide results that are unlikely to be quantitatively influenced [13], particularly if the overall annual growth rate of host populations is negligible.…”

Echinococcus multilocularisintroduction and establishment in wildlife via imported beavers

“…Since 1997, GB has imported beavers from Poland (12), Norway (39) and Germany (55). These beavers have been imported for various reasons including approved introduction programmes, and wildlife and nature parks/reserves.…”