Understanding the Causes of Disease in European Freshwater Crayfish

Abstract:  Native European freshwater crayfish (Astacida, Decapoda) are under severe pressure from habitat alteration, the introduction of nonindigenous species, and epizootic disease. Crayfish plague, an acute disease of freshwater crayfish caused by the fungus-like agent Aphanomyces astaci , was introduced into Europe in the mid-nineteenth century and is responsible for ongoing widespread epizootic mortality in native European populations. We reviewed recent developments and current practices in the field of crayfish pathology. The severity of crayfish plague has resulted in an overemphasis on it. Diagnostic methods for detecting fungi and fungal-like agents, and sometimes culturing them, are frequently the sole techniques used to investigate disease outbreaks in European freshwater crayfish. Consequently, the causes of a significant proportion of outbreaks are undetermined. Pathogen groups well known for causing disease in other crustaceans, such as viruses and rickettsia-like organisms, are poorly understood or unknown in European freshwater crayfish. Moreover, the pathogenic significance of some long-known pathogens of European freshwater crayfish remains obscure. For effective management of this culturally significant and threatened resource, there is an urgent need for researchers, diagnosticians, and resource managers to address the issue of disease in European freshwater crayfish from a broader perspective than has been applied previously.     

Simulation of Rabies Epizootic Process in Fox Populations at a Limited Carrying Capacity of Biotopes

To describe the epizootic process of rabies in fox populations, a model based on a cellular automata network (Toffoli and Margolus, 1991) was constructed. The cell state and the rules of transition from one state to another were determined in accordance with a modification of the previous model based on a differential equation system, which was proposed to describe the epizootics of fox rabies in Western Europe. The new model provides the possibility of simulating spatial heterogeneity and indices of animal mobility related, in particular, to the seasonal features of fox ecology. Calculations were made using population parameters characteristic of biotopes with a low carrying capacity (the steppe zone of Western Siberia). According to the model, the maintenance of rabies epizootics in these biotopes is possible on condition that the mobility of foxes in them is much higher than in the biotopes with a high carrying capacity. This model can be used for prognosis and epidemiological control in natural rabies foci.