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Quantitative competitive PCR as a technique for exploring flea-Yersina pestis dynamics
D M Engelthaler1, B J Hinnebusch, C M Rittner
1Division of Vector Borne Infectious Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado 80522, USA. dengelt@hs.state.az.us
The American Journal of Tropical Medicine and Hygiene
|April 6, 2001
Summary
Higher Yersinia pestis loads in flea vectors are crucial for plague transmission. Oriental rat fleas (Xenopsylla cheopis) showed greater efficiency in acquiring and transmitting the bacteria compared to ground squirrel fleas (Oropsylla montana).
Area of Science:
- Microbiology and Infectious Diseases
- Vector-borne Disease Epidemiology
- Zoonotic Pathogen Research
Background:
- Yersinia pestis is the causative agent of plague, a potentially fatal zoonotic disease.
- Fleas are primary vectors for Yersinia pestis transmission between rodents and humans.
- Understanding the dynamics of Yersinia pestis infection in fleas is critical for plague control.
Purpose of the Study:
- To quantify Yersinia pestis loads in fleas and bacteremia levels in mice.
- To compare the infection and transmission capabilities of two flea species: Xenopsylla cheopis and Oropsylla montana.
- To determine the bacterial thresholds required for flea infection and subsequent transmission to mice.
Main Methods:
- Quantitative competitive polymerase chain reaction (PCR) assay to measure Yersinia pestis.
- Infection of Xenopsylla cheopis and Oropsylla montana fleas with Yersinia pestis via infectious blood meals from mice.
- Monitoring of bacterial loads in fleas and transmission efficiency to naive mice.
- Infection site visualization using a green fluorescent protein (GFP)-tagged Yersinia pestis strain.
Main Results:
- Xenopsylla cheopis exhibited higher infection rates, greater bacterial loads, and faster acquisition of infectiousness than Oropsylla montana.
- Both flea species required approximately 10^6 Yersinia pestis cells per flea for transmission competence.
- Host blood bacterial levels of >= 10^6 bacteria/mL were needed for detectable flea infection, and >= 10^7 bacteria/mL for transmission competence.
Conclusions:
- Bacterial load in the host blood meal is a critical determinant of Yersinia pestis infection and transmission by fleas.
- Xenopsylla cheopis is a more efficient vector for Yersinia pestis compared to Oropsylla montana.
- Specific bacterial thresholds in fleas and host blood are necessary for effective plague transmission.
