Landscape and Residential Variables Associated with Plague-Endemic Villages in the West Nile Region of Uganda

Plague, caused by the bacteria Yersinia pestis , is a severe, often fatal disease. This study focuses on the plagueendemic West Nile region of Uganda, where limited information is available regarding environmental and behavioral risk factors associated with plague infection. We conducted observational surveys of 10 randomly selected huts within historically classified case and control villages (four each) two times during the dry season of 2006 ( N = 78 case huts and N = 80 control huts), which immediately preceded a large plague outbreak. By coupling a previously published landscape-level statistical model of plague risk with this observational survey, we were able to identify potential residence-based risk factors for plague associated with huts within historic case or control villages (e.g., distance to neighboring homestead and presence of pigs near the home) and huts within areas previously predicted as elevated risk or low risk (e.g., corn and other annual crops grown near the home, water storage in the home, and processed commercial foods stored in the home). The identified variables are consistent with current ecologic theories on plague transmission dynamics. This preliminary study serves as a foundation for future case control studies in the area

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

Current control strategies to combat Lyme disease in the north-central and eastern U.S.

Lyme disease is an emerging infectious disease accounting for more than 90% of all reported vector-borne diseases in the United States. In the eastern U.S., the deer tick Ixodes scapularis carries the spirochete Borrelia burgdorferi, which causes the disease. The main reservoir for the spirochete in the wild is the white-footed mouse Peromyscus leucopus, which serves as the most common blood-meal host for the larval and nymphal life stages of the tick. Additionally, the enzootic cycle includes the white-tailed deer Odocoileus virginianus. As the human incidence of Lyme disease continues to increase, effective intervention methods are needed. Control methods for decreasing risk of contracting Lyme disease have been developed and center on targeting the tick or the wildlife hosts that harbor the tick vector. Personal protective measures have also been developed to protect individuals potentially exposed

Current control strategies to combat Lyme disease in the north-central and eastern U.S.

Lyme disease is an emerging infectious disease accounting for more than 90% of all reported vector-borne diseases in the United States. In the eastern U.S., the deer tick Ixodes scapularis carries the spirochete Borrelia burgdorferi, which causes the disease. The main reservoir for the spirochete in the wild is the white-footed mouse Peromyscus leucopus, which serves as the most common blood-meal host for the larval and nymphal life stages of the tick. Additionally, the enzootic cycle includes the white-tailed deer Odocoileus virginianus. As the human incidence of Lyme disease continues to increase, effective intervention methods are needed. Control methods for decreasing risk of contracting Lyme disease have been developed and center on targeting the tick or the wildlife hosts that harbor the tick vector. Personal protective measures have also been developed to protect individuals potentially exposed

Epizoology and response to the bioweapon use of the plague organism, Yersinia pestis, in commensal rodents

The increased risk of terrorism with biological agents has been well documented. In response, the United States has established an extensive infrastructure to counteract deliberate disease epidemics that would follow bioterrorism attacks. The plague organism, Yersinia pestis, has been identified as a Category A biological agent by the Centers for Disease Control and Prevention. The response to the use of Y. pestis as a bioweapon, aerosolized and released to a target population, would first involve the treatment and containment of the disease in humans. As the initial impacts of the first round of human infections occur, the possibility exists that the disease could infect commensal rodent populations. If the disease were to progress in rodents, the rodents would suffer mortality and their plague-infected fleas would seek new hosts, potentially including human hosts, and cause a second disease epidemic in humans. This paper outlines the epizoology of the bioweapon use of Y. pestis to commensal rodents, identifies U.S. localities of concern, and suggests control and surveillance strategies in response to a bioterrorism attack of this nature

INVASIVE RATS AND BUBONIC PLAGUE IN NORTHWEST UGANDA

Major introductions of roof rats (Rattus rattus) likely occurred in the ports of East Africa during the Third Plague Pandemic in the late 1800’s. Transport via trains, boats, and trucking likely introduced this species to inland areas of East Africa, ultimately including Northwest Uganda. Historic plague outbreaks occurred during the early part of the 20th century and continue to cause a human disease burden in the West Nile region of NW Uganda via the bubonic, septicemic, and pneumonic forms. Four field sites in this area were trapped to determine the rodent species composition in commensal and peridomestic areas of villages and associated flea burdens of the rodents. Rattus rattus were the most prevalent rodent trapped in commensal areas followed by the Nile rat (Arvicanthis niloticus). The most common peridomestic species of rodent was the Nile rat. Other peridomestic rodent species captured included, Mastomys natalensis, Lophuromys flavopunctatus, L. sikapusi, Gerbil (Tatera spp.), Lemniscomys spp., and 4 unknown species. Flea burdens on commensal R. rattus averaged 1.7±1.2 fleas per animal and on all peridomestic rodents, average 2.0±0.7 per animal. Additionally, commensal areas were sampled to determine free-living flea populations. Burrow swabbing indicated an average 0.19±0.12 fleas/burrow. Lighted flea traps averaged 1.3±0.6 fleas per household and dark flea traps averaged 0.5±0.4 fleas per household

Landscape and Residential Variables Associated with Plague-Endemic Villages in the West Nile Region of Uganda

Plague, caused by the bacteria Yersinia pestis , is a severe, often fatal disease. This study focuses on the plagueendemic West Nile region of Uganda, where limited information is available regarding environmental and behavioral risk factors associated with plague infection. We conducted observational surveys of 10 randomly selected huts within historically classified case and control villages (four each) two times during the dry season of 2006 ( N = 78 case huts and N = 80 control huts), which immediately preceded a large plague outbreak. By coupling a previously published landscape-level statistical model of plague risk with this observational survey, we were able to identify potential residence-based risk factors for plague associated with huts within historic case or control villages (e.g., distance to neighboring homestead and presence of pigs near the home) and huts within areas previously predicted as elevated risk or low risk (e.g., corn and other annual crops grown near the home, water storage in the home, and processed commercial foods stored in the home). The identified variables are consistent with current ecologic theories on plague transmission dynamics. This preliminary study serves as a foundation for future case control studies in the area

Seasonal fluctuations of small mammal and flea communities in a Ugandan plague focus: evidence to implicate Arvicanthis niloticus and Crocidura spp. as key hosts in Yersinia pestis transmission

BACKGROUND: The distribution of human plague risk is strongly associated with rainfall in the tropical plague foci of East Africa, but little is known about how the plague bacterium is maintained during periods between outbreaks or whether environmental drivers trigger these outbreaks. We collected small mammals and fleas over a two year period in the West Nile region of Uganda to examine how the ecological community varies seasonally in a region with areas of both high and low risk of human plague cases. METHODS: Seasonal changes in the small mammal and flea communities were examined along an elevation gradient to determine whether small mammal and flea populations exhibit differences in their response to seasonal fluctuations in precipitation, temperature, and crop harvests in areas within (above 1300 m) and outside (below 1300 m) of a model-defined plague focus. RESULTS: The abundance of two potential enzootic host species (Arvicanthis niloticus and Crocidura spp.) increased during the plague season within the plague focus, but did not show the same increase at lower elevations outside this focus. In contrast, the abundance of the domestic rat population (Rattus rattus) did not show significant seasonal fluctuations regardless of locality. Arvicanthis niloticus abundance was negatively associated with monthly precipitation at a six month lag and positively associated with current monthly temperatures, and Crocidura spp. abundance was positively associated with precipitation at a three month lag and negatively associated with current monthly temperatures. The abundance of A. niloticus and Crocidura spp. were both positively correlated with the harvest of millet and maize. CONCLUSIONS: The association between the abundance of several small mammal species and rainfall is consistent with previous models of the timing of human plague cases in relation to precipitation in the West Nile region. The seasonal increase in the abundance of key potential host species within the plague focus, but not outside of this area, suggests that changes in small mammal abundance may create favorable conditions for epizootic transmission of Y. pestis which ultimately may increase risk of human cases in this region