Spatiotemporal analysis of bubonic plague in Pernambuco, northeast of Brazil: Case study in the municipality of Exu

Abstract

Along with other countries in America, plague reached Brazil through the sea routes during the third pandemic. A brief ports phase was followed by an urban phase that took place in smaller inland cities and finally, it attained the rural area and established several foci where the ecological conditions were suitable for its continued existence. However, the geographic dispersion of plague in Brazil is still poorly studied. To better understand the disease dynamics, we accessed satellite-based data to trace the spatial occurrence and distribution of human plague cases in Pernambuco, Northeastern Brazil and using the municipality of Exu as study case area. Along with the satellite data, a historical survey using the Plague Control Program files was applied to characterize the spatial and temporal dispersion of cases in the period of 1945–1976. Kernel density estimation, spatial and temporal clusters with statistical significance and maximum entropy modeling were used for spatial data analysis, by means of the spatial analysis software packages. The use of geostatistical tools allowed evidencing the shift of the infection from the urban to the wild-sylvatic areas and the reemergence of cases after a period of quiescence, independent of the reintroduction from other plague areas.

Spatial and Temporal Distribution of Rodents during the Epizootic and Enzootic Periods of Plague, with a Focus on Exu, Northeastern Brazil

“…The plague reappeared in rural areas after a six-year inter-epizootic period and disseminated among the wild fauna practically throughout the municipality territory. According to Figure 3A-F, the dispersal area of the rodents in the present study overlapped with the sites of the distribution of the human cases shown by Fernandes et al [11].…”

“…In a previous study in this same plague area, the transition of the infection from urban to rural areas was observed [ 11 ]. The plague reappeared in rural areas after a six-year inter-epizootic period and disseminated among the wild fauna practically throughout the municipality territory.…”

“…Commensal rat (R. rattus) control includes educative measures for proper grain storage; eliminating rats by clearing the land around houses, thereby making the environment unsuitable for them; and rat extermination, using rodenticides [7,20]. Flea control was carried out using the insecticides DDT (Dichlorodiphenyltrichloroethane) and BHC (Benzene hexachloride), which unfortunately led to the selection of resistance, by continuous pressure, of rat fleas (Xenopsylla cheopis) and human fleas (Pulex irritans) explaining the ineffectiveness of preventive measures based on the continuous use of these insecticides [10,11,16,34].…”

“…The plague disappeared suddenly in this focus area from 1975 [ 11 ]. This may have been associated with the rarefaction of the susceptible species, mainly the population of N. lasiurus , which is considered the amplifier host.…”

“…Indeed, the Kernel density analysis (KDE) of the number of cases reported in Pernambuco revealed that the municipality of Exu is at higher risk for the occurrence of plague. Exu appeared at the epicenter of the Kernel patch, which radiates in decreasing intensity as it moves away from the plateau slope towards the plains and neighboring municipalities [ 11 ].…”