A survey of rat ectoparasites collected over a two-year period in the central city area of Detroit, Michigan, is reported. Results indicate that only live captured rats, not treated with cyanogas, give reliable indices of ectoparasite infestations. A wet combing method involving immersion in 70% isopropyl alcohol and passage through filter paper for recovery and subsequent temporary storage of the ectoparasites is described. This recovery method proved superior when compared to other (both dry and wet) methods. It proved especially efficient in recovery of minute ectoparasites such as the mite Radfordia ensifera, usually missed by conventional methods. The authors believe this method has potential for field use. The flea population of Detroit rats, when compared to surveys from comparable areas, shows a somewhat higher flea index. Xenopsylla cheopis and Nosopsyllus fasciatus are the prevalent fleas on Detroit rats; 66.2% of total fleas recovered were X. cheopis. However, 39 of the live trapped rats harbored X. cheopis and 45 harbored N. fasciatus. Eleven rats had double infections with X. cheopis and N. fasciatus. The present survey differs significantly from other surveys in the total percent infection (25.83%) with R. ensifera. Other surveys give fractional percent infection or no infection with this mite. This difference is due to the superior recovery methods described and used in the Detroit survey.
Professor of Parasitology, Department of Biology and Department of Medical Microbiology.