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

Flea-Associated Bacterial Communities across an Environmental Transect in a Plague-Endemic Region of Uganda.

The vast majority of human plague cases currently occur in sub-Saharan Africa. The primary route of transmission of Yersinia pestis, the causative agent of plague, is via flea bites. Non-pathogenic flea-associated bacteria may interact with Y. pestis within fleas and it is important to understand what factors govern flea-associated bacterial assemblages. Six species of fleas were collected from nine rodent species from ten Ugandan villages between October 2010 and March 2011. A total of 660,345 16S rRNA gene DNA sequences were used to characterize bacterial communities of 332 individual fleas. The DNA sequences were binned into 421 Operational Taxonomic Units (OTUs) based on 97% sequence similarity. We used beta diversity metrics to assess the effects of flea species, flea sex, rodent host species, site (i.e. village), collection date, elevation, mean annual precipitation, average monthly precipitation, and average monthly temperature on bacterial community structure. Flea species had the greatest effect on bacterial community structure with each flea species harboring unique bacterial lineages. The site (i.e. village), rodent host, flea sex, elevation, precipitation, and temperature also significantly affected bacterial community composition. Some bacterial lineages were widespread among flea species (e.g. Bartonella spp. and Wolbachia spp.), but each flea species also harbored unique bacterial lineages. Some of these lineages are not closely related to known bacterial diversity and likely represent newly discovered lineages of insect symbionts. Our finding that flea species has the greatest effect on bacterial community composition may help future investigations between Yersinia pestis and non-pathogenic flea-associated bacteria. Characterizing bacterial communities of fleas during a plague epizootic event in the future would be helpful

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

Mantel Tests comparing bacterial community structure to environmental parameters.

<p>MAP: Mean Annual Precipitation, Precipitation: Average monthly precipitation.</p><p>Mantel Tests comparing bacterial community structure to environmental parameters.</p