Flea Diversity as an Element for Persistence of Plague Bacteria in an East African Plague Focus

Plague is a flea-borne rodent-associated zoonotic disease that is caused by Yersinia pestis and characterized by long quiescent periods punctuated by rapidly spreading epidemics and epizootics. How plague bacteria persist during inter-epizootic periods is poorly understood, yet is important for predicting when and where epizootics are likely to occur and for designing interventions aimed at local elimination of the pathogen. Existing hypotheses of how Y. pestis is maintained within plague foci typically center on host abundance or diversity, but little attention has been paid to the importance of flea diversity in enzootic maintenance. Our study compares host and flea abundance and diversity along an elevation gradient that spans from low elevation sites outside of a plague focus in the West Nile region of Uganda (∼725–1160 m) to higher elevation sites within the focus (∼1380–1630 m). Based on a year of sampling, we showed that host abundance and diversity, as well as total flea abundance on hosts was similar between sites inside compared with outside the plague focus. By contrast, flea diversity was significantly higher inside the focus than outside. Our study highlights the importance of considering flea diversity in models of Y. pestis persistence

Effects of temperature on the transmission of Yersinia Pestis by the flea, Xenopsylla Cheopis, in the late phase period

<p>Abstract</p> <p>Background</p> <p>Traditionally, efficient flea-borne transmission of <it>Yersinia pestis</it>, the causative agent of plague, was thought to be dependent on a process referred to as blockage in which biofilm-mediated growth of the bacteria physically blocks the flea gut, leading to the regurgitation of contaminated blood into the host. This process was previously shown to be temperature-regulated, with blockage failing at temperatures approaching 30°C; however, the abilities of fleas to transmit infections at different temperatures had not been adequately assessed. We infected colony-reared fleas of <it>Xenopsylla cheopis </it>with a wild type strain of <it>Y. pestis </it>and maintained them at 10, 23, 27, or 30°C. Naïve mice were exposed to groups of infected fleas beginning on day 7 post-infection (p.i.), and every 3-4 days thereafter until day 14 p.i. for fleas held at 10°C, or 28 days p.i. for fleas held at 23-30°C. Transmission was confirmed using <it>Y. pestis</it>-specific antigen or antibody detection assays on mouse tissues.</p> <p>Results</p> <p>Although no statistically significant differences in per flea transmission efficiencies were detected between 23 and 30°C, efficiencies were highest for fleas maintained at 23°C and they began to decline at 27 and 30°C by day 21 p.i. These declines coincided with declining median bacterial loads in fleas at 27 and 30°C. Survival and feeding rates of fleas also varied by temperature to suggest fleas at 27 and 30°C would be less likely to sustain transmission than fleas maintained at 23°C. Fleas held at 10°C transmitted <it>Y. pestis </it>infections, although flea survival was significantly reduced compared to that of uninfected fleas at this temperature. Median bacterial loads were significantly higher at 10°C than at the other temperatures.</p> <p>Conclusions</p> <p>Our results suggest that temperature does not significantly effect the per flea efficiency of <it>Y. pestis </it>transmission by <it>X. cheopis</it>, but that temperature is likely to influence the dynamics of <it>Y. pestis </it>flea-borne transmission, perhaps by affecting persistence of the bacteria in the flea gut or by influencing flea survival. Whether <it>Y. pestis </it>biofilm production is important for transmission at different temperatures remains unresolved, although our results support the hypothesis that blockage is not necessary for efficient transmission.</p

SHORT REPORT: FOX SQUIRREL (\u3ci\u3eSCIURUS NIGER\u3c/i\u3e) ASSOCIATIONS WITH WEST NILE VIRUS

Tree squirrels (Sciurus spp.) have been recently shown to be commonly exposed to West Nile virus (WNV). Many characteristics of WNV infections in tree squirrels are unknown. To better understand WNV associations in fox squirrels (S. niger), we conducted mark-recapture sampling (N=72) and radio telemetry to study the longitudinal seroprevalence, seroconversions, and ectoparasites of these animals during 2005–2006 in northern Colorado. Five seroconversions were documented during this study. The majority of seroconversions occurred during the late summer/ fall months. However, one seroconversion was documented over the time period of February to late March 2005. Fleas (Orchopeas howardi) were tested for WNV RNA using real-time PCR techniques. No WNV RNA positive fleas (N = 33) were detected. In addition, urine samples (N = 17) opportunistically collected from fox squirrels were negative for WNV RNA. Results indicate that seroconversions can be observed in fox squirrels during low WNV transmission years

Development of a genetic marker to distinguish between Pulex irritans and Pulex simulans, two potential flea vectors of plague transmission

Sea ice drift and surface temperature were measured by the Compact Air-Launched Ice Beacon (CALIB) 2015C11 drifting on Arctic sea ice. The buoy was deployed on first year/second year ice during MELTEX-II 2015 (Impact of sea ice thickness, sea ice topography and MELT ponds on the energy and momentum EXchange between atmosphere and sea ice). The time series describes the position and additional parameters of the buoy between 03 Jul 2015 and 08 Sep 2015 in sample intervals of 10 minutes. The data set has been processed, including the removal of obvious inconsistencies (missing values)