title: Effects of low-temperature flea maintenance on the transmission of Yersinia pestis by Oropsylla montana.
abstract: Yersinia pestis, the causative agent of plague, is primarily a rodent-associated, flea-borne zoonosis maintained in sylvatic foci throughout western North America. Transmission to humans is mediated most commonly by the flea vector Oropsylla montana and occurs predominantly in the southwestern United States. With few exceptions, previous studies showed O. montana to be an inefficient vector at transmitting Y. pestis at ambient temperatures, particularly when such fleas were fed on susceptible hosts more than a few days after ingesting an infectious blood meal. We examined whether holding fleas at subambient temperatures affected the transmissibility of Y. pestis by this vector. An infectious blood meal containing a virulent Y. pestis strain (CO96-3188) was given to colony-reared O. montana fleas. Potentially infected fleas were maintained at different temperatures (6°C, 10°C, 15°C, or 23°C). Transmission efficiencies were tested by allowing up to 15 infectious fleas to feed on each of 7 naïve CD-1 mice on days 1-4, 7, 10, 14, 17, and 21 postinfection (p.i.). Mice were monitored for signs of infection for 21 days after exposure to infectious fleas. Fleas held at 6°C, 10°C, and 15°C were able to effectively transmit at every time point p.i. The percentage of transmission to naïve mice by fleas maintained at low temperatures (46.0% at 6°C, 71.4% at 10°C, 66.7% at 15°C) was higher than for fleas maintained at 23°C (25.4%) and indicates that O. montana fleas efficiently transmit Y. pestis at low temperatures. Moreover, pooled percent per flea transmission efficiencies for flea cohorts maintained at temperatures of 10°C and 15°C (8.67% and 7.87%, respectively) showed a statistically significant difference in the pooled percent per flea transmission efficiency from fleas maintained at 23°C (1.94%). This is the first comprehensive study to demonstrate efficient transmission of Y. pestis by O. montana fleas maintained at temperatures as low as 6°C. Our findings further contribute to the understanding of plague ecology in temperate climates by providing support for the hypothesis that Y. pestis is able to overwinter within the flea gut and potentially cause infection during the following transmission season. The findings also might hold implications for explaining the focality of plague in tropical regions.
authors.affiliation: Bacterial Diseases Branch, Division of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, USA.
authors.forename: Shanna K
authors.initials: SK
authors.lastname: Williams
authors.forename: Anna M
authors.initials: AM
authors.lastname: Schotthoefer
authors.forename: John A
authors.initials: JA
authors.lastname: Montenieri
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Holmes
authors.forename: Sara M
authors.initials: SM
authors.lastname: Vetter
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Gage
authors.forename: Scott W
authors.initials: SW
authors.lastname: Bearden
mesh_terms: D000818:Animals; D004197:Disease Reservoirs; D005260:Female; D058267:Flea Infestations / Q000469:parasitology*; D006801:Humans; D007303:Insect Vectors / Q000382:microbiology*; D008297:Male; D051379:Mice; D010930:Plague / Q000382:microbiology / Q000635:transmission*; D012621:Seasons; D005423:Siphonaptera / Q000382:microbiology*; D013047:Specific Pathogen-Free Organisms; D013696:Temperature; D015010:Yersinia pestis / Q000472:pathogenicity / Q000502:physiology*; D015047:Zoonoses