Human Plague in the Southwestern United States, 1957–2004: Spatial Models of Elevated Risk of Human Exposure to <I>Yersinia pestis</I>

Abstract

Plague is a rare but highly virulent flea-borne zoonotic disease caused by the Gram-negative bacterium Yersinia pestis Yersin. Identifying areas at high risk of human exposure to the etiological agent of plague could provide a useful tool for targeting limited public health resources and reduce the likelihood of misdiagnosis by raising awareness of the disease. We created logistic regression models to identify landscape features associated with areas where humans have acquired plague from 1957 to 2004 in the four-corners region of the United States (Arizona, Colorado, New Mexico, and Utah), and we extrapolated those models within a geographical information system to predict where plague cases are likely to occur within the southwestern United States disease focus. The probability of an area being classified as high-risk plague habitat increased with elevation up to approximately 2300 m and declined as elevation increased thereafter, and declined with distance from key habitat types (e.g., southern Rocky Mountain piñon--juniper [Pinus edulis Engelm. and Juniperus spp.], Colorado plateau piñon--juniper woodland, Rocky Mountain ponderosa pine (Pinus ponderosa P.& C. Lawson var. scopulorum), and southern Rocky Mountain juniper woodland and savanna). The overall accuracy of the model was >82%. Our most conservative model predicted that 14.4% of the four-corners region represented a high risk of peridomestic exposure to Y. pestis.

Assessing Human Risk of Exposure to Plague Bacteria in Northwestern Uganda Based on Remotely Sensed Predictors

“…However, 11% of case homes were situated in areas classified as low risk. We assumed that, similar to other plague foci, 17,18,[44][45][46][47] most plague cases occur in the peridomestic setting. This finding was supported by the observation that a higher proportion of case homes, relative to controls, were located within pixels classified as elevated risk.…”

“…Geographic Information Systems (GIS) and Remote Sensing (RS) technology coupled with statistical modeling have been useful in generating risk maps that display this spatial heterogeneity and such outputs may aid in identifying previously uncharacterized plague foci. [17][18][19][20][21][22] In recent decades, most human plague infections have been reported from eastern Africa and Madagascar. 16,23 The GISbased models have identified widespread areas of risk on the African continent, and they have determined that ecological predictors of risk are variable among these foci.…”

“…The objective of our model was to classify the West Nile region of Uganda into areas of elevated or low risk of human exposure to plague bacteria. In accordance with reported methods, 17 logistic regression models were constructed to evaluate the association between the probability of a grid cell being classified as high risk and its environmental attributes (described above). The first candidate model included variables that were previously identified as predictive of risk at a parish-level scale (i.e., elevation, brightness, greenness, wetness).…”

Flea Diversity and Infestation Prevalence on Rodents in a Plague-Endemic Region of Uganda

“…Table 2 Seasonal trends in flea infestation by host species and district ated with domestic or peridomestic settings. [27][28][29][30][31][32] Furthermore, because of their high vector efficiency, broad host preferences, and close association with human dwellings, X. cheopis and X. brasiliensis have been implicated as primary vectors to humans in domestic and peridomestic settings. 7,10,19 Because of the high abundance of R. rattus infested with X. cheopis or X. brasiliensis in and around human dwellings in Arua and Nebbi districts, respectively, it is likely that, during epizootic periods when a high proportion of these fleas may be infected with Y. pestis , domestic and peridomestic areas pose the greatest risk to humans.…”

Predicting Potential Risk Areas of Human Plague for the Western Usambara Mountains, Lushoto District, Tanzania

“…37 In the western United States, a geographical information system (GIS) -based model indicated that suitability for plague increases for elevations up to 2,129 m but declines at higher elevations. 38 Besides elevation, plague occurrences seem to be linked to seasonal vegetation changes, resulting from rainfall variability through the year, and to moderate EVI values and reasonably high seasonality, suggesting that forests are not suitable for plague; however, because people do not frequently live in the forests, this conclusion could be misleading.…”