Evaluating the spatial ecology of anthrax in North America: examining epidemiological components across multiple geographic scales using a GIS-based approach

This dissertation explores the spatial ecology and potential pathways of infection of anthrax, Bacillus anthracis, in North America. A multi-scale approach was used to evaluate the components required for disease agent survival in the environment, interactions with wildlife, and the potential role that vectors play in anthrax transmission. First, ecological niche modeling with the Genetic Algorithm for Rule-set Production (GARP) was used to predict the geographic distribution of anthrax in the continental U.S. using case data from outbreaks between 1957 and 2005. These results were then used to produce the first quantitative, continental scale predictions of anthrax in Mexico. At the meso-scale, the route of transmission in white-tailed deer is unknown, despite a large number of outbreaks in wild deer in Texas in recent years (2001 – 2005). To determine the interactions between deer and potential anthrax sources, two pilot studies were conducted on 1) the distribution of biting flies in relation to anthrax cases to evaluate the potential role of hematophagous flies as vectors, and 2) the summer home ranges of deer in relation to fly densities and carcass locations. The results of the GARP studies support the use of the technique for modeling the niche of this disease and suggest a central corridor of anthrax habitat from southwest Texas to the Canadian border, with disjunct areas in the Pacific Northwest and California. Mexico’s predicted areas were extensions of the Texas and California ranges. The deer study suggests that deer interactions with spores occur within a limited home range in Texas and long-distance movement of spores is unlikely by individual deer. Biting fly densities were highest in areas of known anthrax infection and lowest in areas where case-positive deer have not been identified, suggesting that flies may play a role in disease transmission, either through mechanical transmission or through increased nuisance that leads to immuno-suppression in deer. This dissertation presents the first continental-scale predictions for the geographic distribution of anthrax in the U.S. and Mexico. Additionally, this is the first known study to evaluate spatial patterns between known cases, fly densities, and animal movements

Characterizing spatially explicit patterns of Antibiotic Resistance in the marine environment using top-level marine predators

This research is the first known study to characterize spatially explicit patterns of Antibiotic Resistance (ABR) in top-level marine predators. A total of 134 viable bacteria samples were isolated from cloacal swabs of seven shark species and one teleost species and then stratified by geographic location. Samples were collected using sterile rayon-tipped culturettes and transported to the LSU-SVM for classification and antibiotic resistance analyses using the Kirby-Bauer method. Samples were characterized by Gram-stain and morphology and placed into three groups: 1) Gram-negative rods, 2) Gram-positive cocci, or 3) Gram-positive rods. Prevalence rates were calculated for each study site as the number of isolates resistant to at least one drug divided by the total number of isolates in each location. Prevalence rates for each study location were: 1) Belize: 75%, 2) Florida Keys: 86.5%, 3) Coastal Louisiana: 62%, 4) Louisiana Offshore-sharks: 52%, 5) Louisiana Offshore-redfish: 91.7%, and 6) Massachusetts: 87.5%. High prevalence rates in Massachusetts prompted the removal of penicillin from analysis to evaluate potential intrinsic resistance, as the majority of Massachusetts isolates were Gram-negative and resistance to penicillin was assumed. Rates dropped dramatically with the removal of penicillin. Spatial variation existed between locations allowing for intra-specific comparisons between sharks in Belize and Florida to evaluate potential geographic differences that might influence ABR patterns. Inter-specific comparisons between redfish and sharks from Louisiana offshore waters demonstrated significantly higher levels in redfish, which may be due to older age and longer exposure in redfish populations. Florida demonstrated the highest prevalence in sharks and the Louisiana redfish had the highest ABR prevalence of all populations sampled. Both results suggest that top-level predatory fishes can serve as sentinels for ABR in the marine environment, and that multiple species should be sampled. Additionally, spatial variation was documented and future work on ABR surveillance of marine fishes should incorporate geographically stratified data collection and spatial analyses. A color atlas is provided with maps of prevalence rates, intrinsic prevalence rates, multi-drug resistance rates, and a 10-map series of categorical maps showing the spatial patterns of resistance for five important antibiotic drugs

Buffalo, Bush Meat, and the Zoonotic Threat of Brucellosis in Botswana

Brucellosis is a zoonotic disease of global importance infecting humans, domestic animals, and wildlife. Little is known about the epidemiology and persistence of brucellosis in wildlife in Southern Africa, particularly in Botswana.Archived wildlife samples from Botswana (1995-2000) were screened with the Rose Bengal Test (RBT) and fluorescence polarization assay (FPA) and included the African buffalo (247), bushbuck (1), eland (5), elephant (25), gemsbok (1), giraffe (9), hartebeest (12), impala (171), kudu (27), red lechwe (10), reedbuck (1), rhino (2), springbok (5), steenbok (2), warthog (24), waterbuck (1), wildebeest (33), honey badger (1), lion (43), and zebra (21). Human case data were extracted from government annual health reports (1974-2006).Only buffalo (6%, 95% CI 3.04%-8.96%) and giraffe (11%, 95% CI 0-38.43%) were confirmed seropositive on both tests. Seropositive buffalo were widely distributed across the buffalo range where cattle density was low. Human infections were reported in low numbers with most infections (46%) occurring in children (<14 years old) and no cases were reported among people working in the agricultural sector.Low seroprevalence of brucellosis in Botswana buffalo in a previous study in 1974 and again in this survey suggests an endemic status of the disease in this species. Buffalo, a preferred source of bush meat, is utilized both legally and illegally in Botswana. Household meat processing practices can provide widespread pathogen exposure risk to family members and the community, identifying an important source of zoonotic pathogen transmission potential. Although brucellosis may be controlled in livestock populations, public health officials need to be alert to the possibility of human infections arising from the use of bush meat. This study illustrates the need for a unified approach in infectious disease research that includes consideration of both domestic and wildlife sources of infection in determining public health risks from zoonotic disease invasions

Mapped distribution of survey results for brucellosis antibodies among buffalo in Botswana in relation to average cattle counts (orange color ramp) and average buffalo counts (blue color ramp; Inset A); Inset B illustrates the distribution of FPA positive animals identified in this study (red squares) relative to historical samples screened by Cooper and Carmichael (1974; purple boxes).

<p>Green shaded areas are gazetted as conservation land use such as national parks, reserves, and wildlife management areas.</p

Map of Botswana showing annual range of greenness (NDVI) from temporal Fourier processed AVHRR satellite data illustrating the extreme variation in vegetation associated with rainfall, particularly in northern Botswana.

<p>Red areas indicate zones with the most dramatic change in vegetation over the year. The green area indicates the location of Chobe National Park (referred to in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032842#pone-0032842-g004" target="_blank">Figure 4</a>).</p

Seasonal changes in total biomass (livestock and wildlife combined) in northeastern Botswana from aerial animal surveys conducted by the Department of Wildlife and National Parks in the dry season (A-1990, B-1999) and wet season (C-1990, D-1999).

<p>Red cells represent increases in total biomass above the annual mean. Blue cells represent decreases below the annual mean. The green line represents the Chobe National Park boundary for reference. Note: the park is not fenced and wildlife populations occur throughout the area at different densities and intensity of overlap with humans.</p

Seroprevalence of brucellosis among sampled buffalo and giraffe by administrative districts and year of sampling (see Figure 3 for map of districts).

<p>Seroprevalence of brucellosis among sampled buffalo and giraffe by administrative districts and year of sampling (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032842#pone-0032842-g003" target="_blank">Figure 3</a> for map of districts).</p

Estimated buffalo population numbers for Northern Botswana (1988–2006) from dry season aerial surveys conducted by the Department of Wildlife and National Parks.

<p>Estimated buffalo population numbers for Northern Botswana (1988–2006) from dry season aerial surveys conducted by the Department of Wildlife and National Parks.</p

Cattle distribution mapped across Africa corrected to 2000 country estimates from the Food and Agricultural Organization (FAO) Gridded Livestock Production and Health Atlas (GLiPHA) livestock data set (Inset A) [50]<b>.</b>

<p>Changes in cattle density from 2000 to 2005 are illustrated in the Inset B (low to high, blue to red color ramp).</p

Human cases of brucellosis are presented by age, sex, occupation, and year of diagnosis.

<p>Patients marked with (*) were identified as being ≥14 years of age and were, thus, grouped to the next highest age category. Categorical data choices included: professional/technician, administration, clerk, sale, service, agriculture, production, transport, labor, housewife, student, and child. ND denotes no available data.</p