Contemporary Views on the Interrelationships Between Fleas and the Pathogens of Human and Animal Diseases

The fleas, like any other group of parasitic, bloodsucking arthropods, have been exposed to contact with various pathogenic agents throughout the protracted period of their existence. As a result of this association, the present interrelationships between the fleas and the pathogens of zoonoses and anthroponoses have evolved. Various indices are used to appraise the relationship between a vector and a causative agent (pathogen): the capacity of the causative agent to reproduce in the vector, the duration of their joint sojourn, the pathogenic effect, etc. However, these relationships most vividly manifest themselves in the mechanism of transmission that has evolved historically for the given disease. It is in the formation and realization of the mechanism of transmission that the maximal available adaptive possibilities between the pathogen and the vector are most vividly expressed, since the parasitic nature of the pathogen presupposes, as a condition of the existence of the species, the obligatory and multiple transmission from one host to another. Such a methodological approach to the assessment of the relationships between the vector and the causative agent of the transmissive disease stems from the recognition of the ecological principle of existence of natural foci (40) and the theory of the mechanism of transmission (28). For the time being the extent of our knowl­ edge of the peculiarities of transmission permits us to consider relationships of only six species of pathogens with the order Siphonaptera (Table I).