A Study of the Rodent-Ectoparasite Population of Jacksonville, Fla.

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Abstract
Evidence indicates that infectibility of a community with bubonic plague or endemic typhus fever is correlated with climatic conditions operating through effects on rodent ectoparasites. This is the first of a series of studies on representative areas attempting to establish a basis for the systematic analysis of epidemiologic factors. All fleas from 4663 live-trapped rats and all mites and lice from 524 rats were identified and the data analyzed for possible epidemiologic factors. Analysis of seasonal levels of parasitization showed the flea Xenopsylla cheopis and the mite Laelaps hawaiiensis to be the only spp. exhibiting statistically significant summer maxima. Both spp. showed high positive correlations with air temp. Analysis for section of city, type of premises, and location of trap showed a significant predominance of X. cheopis and L. hawaiiensis in the commercial section over the waterfront and residential districts. Significant differences were not observed for sp. of rat or type of premises, so it is suggested that the known affinity of typhus infection for food-handling establishments is related to the larger rat populations observed on such premises. Choice of a satisfactory index of flea abundance is discussed. Since such frequency distrs. are skewed in the direction of abnormally high counts on some rats, a new type of index is derived by using a fitted curve to determine objectively a working upper limit to the distr. This type of index as well as the arithmetic mean and the % of infested rats is used throughout the study.

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