By H. J. Bensted, W. Bulloch, L. Dudgeon, A. G. Gardner, E. D. W. Greig, D. Harvey, W. F. Harvey, T. J. Mackie, R. A. O'Brien, H. M. Perry, H. Scutze, P. Bruce White, W. J. Wilson. London, 1929. His Majesty's Stationery Office. Pp. 1–482
by A. Trevor Willis, M.D., B.S. (Melb.), Ph.D. (Leeds), M.C.Path., M.C.P.A., Reader in Microbiology, Monash University, formerly Lecturer in Bacteriology, University of Leeds. xiv + 234 pages, illustrated, second edition. Butterworth Inc., Washington. 1965. $8.50
1 Laboratory of Microbial Structure and Function, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana 59840, USA. firstname.lastname@example.org
The prevalence of infectivity within a vector population is a critical factor in arthropod-borne disease epidemiology but it is difficult to estimate. In the case of bubonic plague, infective flea vectors contain large numbers of Yersinia pestis within a bacterial mass that blocks the flea's foregut, and only such blocked fleas are important for biologic transmission. A bacterial quantitation method could therefore be used to assess the prevalence of plague-infective (blocked) fleas in a population. We developed a standard, curve-based, competitive polymerase chain reaction (PCR) procedure to quantitate Y. pestis in individual fleas. The quantitative PCR (Q-PCR) method equaled a colony count reference method in accuracy and precision when evaluated using mock samples and laboratory-infected fleas. The Q-PCR was more reliable than colony count, however, for field-collected fleas and for blocked fleas collected after their death. In a sample of fleas collected from a prairie dog colony in the aftermath of a plague epizootic, 48% were infected but less than 2% contained numbers of Y. pestis indicative of blockage. The method provides a means to monitor plague epizootics and associated risks of flea-borne transmission to humans, and is applicable to the study of other vector-borne diseases.