Abstract
The evaluation of the vector efficiency of a species of arthropod incriminated in the transmission of an infectious agent must necessarily take into consideration the following factors: (1) The infection potential, (2) the vector potential, and (3) the transmission potential. The infection potential is based upon the percentage of a given species in which the infection becomes established or the disposition of this species to accept the invasion of the organism of the infection. The vector potential is based upon the percentage of infected individuals which become infective. The transmission potential is the mean number of transmissions effected by a group of infective individuals. The product of these factors will represent the number of transmissions effected by a given number of any species or the vector efficiency.
To determine if a given species of flea was capable of transmitting Pasteurella pestis (Yersin) mass feeding experiments were first conducted. When transmission ability was established in a species this species was then tested to determine the vector efficiency by daily individual feedings. Mass tests were conducted with Diamanus montanus (Baker) and Hoplopsyllus anomalus (Baker), predominant species of the California ground squirrel, Citellus beecheyi (Richardson), Nosopsyllus fasciatus (Bosc) and Xenopsylla cheopis Rothschild, the principal fleas of rats, Rattus spp., Malareus telchinum Rothschild of the field mouse, Microtus californicus (Peale), and Ctenocephalides felis (Curtis) of domestic cats, Felis domestica Linn.
Successful transmissions were obtained with D. montanus, C. felis, N. fasciatus, X. cheopis and H. anomalus. Only one of 3 mass trials with H. anomalus resulted in transmission indicating the possibility that this species may prove to be a rather poor vector.
To determine the vector efficiency experimentally, clean laboratory-reared fleas of each species tested were first fed upon an infected mouse in which the magnitude of bacteremia was known; thereafter each flea was given an opportunity to feed at daily intervals until death upon white mice. Infection of the fleas was determined by means of daily fecal cultures during the life of each flea and by subsequent histological examination.
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