The Flea Malaraeus telchinum a Vector of P. pestis .

In the course of an extensive survey instituted in an important section of the San Francisco Bay region in order to determine the source of the P. pestis demonstrated in pools of fleas, 1,356 rodents (Meadow mice— Microtus californicus 952, Deer mouse— Peromyscus maniculatus 347, Brown rat— Rattus norvegicus 40, and Harvest mice— Reithrodontomys megalotis 17) were trapped. Their ectoparasites were collected and adequate samples of fleas, both males and females, were cleared and identified. The species determinations and host data are listed in Table I.

It was found that Malaraeus telchinumwas by far the most numerous of the fleas found on Microtus californicus, and that this flea outnumbered Nosopsyllus jasciatus about 2 to 1 on Rattus norvegicus. Opisodasys nesiotus was slightly more numerous than Malaraeus telchinum on Peromyscus maniculatus.

Since Malaraeus telchinum was the only species of flea found to parasitize all 3 species of rodents known to be spontaneous hosts for P. pestis, it was deemed imperative to undertake transmission experiments. Such experiments were prompted by the observations of Eskey and Haas 1 who noted that 74 Malaraeus telchinum fed on a plague-infected guinea pig were apparently unable to transmit P. pestis to guinea pigs despite the fact the flea developed blockage.

Wheeler and Douglas2 using white mice as sources for the infection reported the failure of Malar aeus telchinum to transmit P. pestis in mass feeding experiments on white mice. In the experiments herewith reported, Peromyscus maniculatus, Microtus californicus, and the white mouse were used as a source for the infection. The pools of the fleas so infected were permitted to feed on Microtus californicus.

Ten experiments have thus far been completed, and 4 positive transmissions have been obtained as follows: