Human plague: An old scourge that needs new answers

Yersinia pestis, the bacterial causative agent of plague, remains an important threat to human health. Plague is a rodent-borne disease that has historically shown an outstanding ability to colonize and persist across different species, habitats, and environments while provoking sporadic cases, outbreaks, and deadly global epidemics among humans. Between September and November 2017, an outbreak of urban pneumonic plague was declared in Madagascar, which refocused the attention of the scientific community on this ancient human scourge. Given recent trends and plague’s resilience to control in the wild, its high fatality rate in humans without early treatment, and its capacity to disrupt social and healthcare systems, human plague should be considered as a neglected threat. A workshop was held in Paris in July 2018 to review current knowledge about plague and to identify the scientific research priorities to eradicate plague as a human threat. It was concluded that an urgent commitment is needed to develop and fund a strong research agenda aiming to fill the current knowledge gaps structured around 4 main axes: (i) an improved understanding of the ecological interactions among the reservoir, vector, pathogen, and environment; (ii) human and societal responses; (iii) improved diagnostic tools and case management; and (iv) vaccine development. These axes should be cross-cutting, translational, and focused on delivering context-specific strategies. Results of this research should feed a global control and prevention strategy within a “One Health” approach

First Experiences with Low Cost Optical Particle Counters Reveal Spore Emission in Woodlands During Night Time

Background: Monitoring of spores with traps of the Hirst design is labour intensive. A new generation of fully automated, but expensive (>100,000€), systems (e.g. WIBS or Rapid-E) has potential to replace the Hirst trap and can deliver data in real time. When studies require multiple locations with high temporal resolution an alternative approach is therefore needed. The purpose of this study is to evaluate a low cost (~260€) particle counter for real time observations of spores with high temporal resolution. Methods: Three modified low-cost mobile real-time particle counters were placed 1 m above a known source of fungal spores in a woodland near to Worcester in autumn 2017. A Burkard trap and a data logger were placed near the particle counters. Slides from the Burkard trap were analysed with respect to the dominating spores found during the campaign. Data from the particle counter, available every 10 sec in 16 different size bins, have been aggregated to hourly intervals comparable to data from the Burkard trap. Results: The spore counts (Burkard trap) show high night time concentrations of spores relating to the known source and no spores of this type were observed during the day. The results from the particle counter were highly correlated with spore counts, e.g. ascospores found in the size range 12-14um during night-time and nothing during day-time. Data from the weather logger shows that night-time peak concentrations were only found during long periods when relative humidity reached 100%, thus identifying a primary emission process. Discussion & conclusion: The application of a real time particle counter has been used here to demonstrate how processes of spore emissions can be revealed in the real time using low cost equipment. Care must however be taken as they only detect size and not composition. Nevertheless the devices have substantial potential to supplement existing monitoring networks, as personal devices or within process based studies

An Evaluation of the Flea Index as a Predictor of Plague Epizootics in the West Nile Region of Uganda

Abstract Plague is a low incidence flea-borne zoonosis that is often fatal if treatment is delayed or inadequate. Outbreaks occur sporadically and human cases are often preceded by epizootics among rodents. Early recognition of epizootics coupled with appropriate prevention measures should reduce plague morbidity and mortality. For nearly a century, the flea index (a measure of fleas per host) has been used as a measure of risk for epizootic spread and human plague case occurrence, yet the practicality and effectiveness of its use in surveillance programs has not been evaluated rigorously. We sought to determine whether long-term monitoring of the Xenopsylla flea index on hut-dwelling rats in sentinel villages in the plague-endemic West Nile region of Uganda accurately predicted plague occurrence in the surrounding parish. Based on observations spanning ~6 yr, we showed that on average, the Xenopsylla flea index increased prior to the start of the annual plague season and tended to be higher in years when plague activity was reported in humans or rodents compared with years when it was not. However, this labor-intensive effort had limited spatial coverage and was a poor predictor of plague activity within sentinel parishes.</jats:p

Epidemiology, Ecology and Prevention of Plague in the West Nile Region of Uganda: The Value of Long-Term Field Studies

Abstract.Plague, a fleaborne rodent-associated zoonosis, is a neglected disease with most recent cases reported from east and central Africa and Madagascar. Because of its low incidence and sporadic occurrence, most of our knowledge of plague ecology, prevention, and control derives from investigations conducted in response to human cases. Long-term studies (which are uncommon) are required to generate data to support plague surveillance, prevention, and control recommendations. Here we describe a 15-year, multidisciplinary commitment to plague in the West Nile region of Uganda that led to significant advances in our understanding of where and when persons are at risk for plague infection and how to reduce morbidity and mortality. These findings provide data-driven support for several existing recommendations on plague surveillance and prevention and may be generalizable to other plague foci.</jats:p

Effect of Height on Pollen Sampling in Relation to Pollen Exposure at Ground Level

Pollen monitoring networks around the world are mainly based on rooftop-located stations on buildings. Thus, measured airborne pollen levels could be different from ground level, where most allergic individual reside. Until now, the effects of height of sampling on pollen concentration are not well documented. The aim of this meta-analysis was to analyse these effects using a large number of twin sampling stations. Pollen data from 45 twin-stations Hirst-type volumetric spore traps were analyzed, with a maximum distance of 5km between the twin traps, from 25 different locations. To compare the effect of height, the mean of the daily ratio of the amounts of pollen registrered at different heights was used. The values of the lowest station were divided by the higher station. Stations between 1.5m and 50 agl were considered. The results showed that the traps at lower height registered generally higher pollen concentration (average pollen ratio higher than 1), although the behaviour of the ratio differed per pollen type. For instance, both Poaceae and Betula showed that as the height differenc eincreased, the pollen ratio was higher up to a certain height difference when the ratio stabilizes (around 1.5). On the other hand, the standard deviation of the pollen ratio was greater for the traps closer to ground level. Therefore the height difference is a factor which explains the pollen ratio in conjunction with other variables such as the minimum height of the lower trap or the distance between the spore traps. These findings are highly relevant to clinical practice, as the relationship between pollen exposure at ground level and monitored airborne pollen concentrations at roof-top elvel are determined. Thus, the optimal pollen monitoring height could be optimized based on these result