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Modeling the impact of cattle movements on transmission dynamics of bovine tuberculosis

(Mycobacterium bovis) in the United States at local and national scales.


Bovine tuberculosis (TB) is an infectious chronic disease found primarily in cattle, but has been identified in many other North American species. Despite progress in the eradication of bovine TB in the United States, small pockets of infection still exist in cattle and wildlife, and the US spent approximately $33 million on eradication efforts in 2008 alone. To address these issues a working group at the National Institute for Mathematical and Biological Synthesis (NIMBioS) was formed with the goal of developing network models of cattle movement and the spread of bovine TB in the United States.  These models will be used to investigate how wildlife reservoirs and introduction of bovine TB from Mexico affect control strategies and how alternative control and eradication strategies can be developed to improve eradication efforts. Much of the progress in modeling bovine TB has been in European agricultural systems where cattle movement and disease spread data are highly detailed. The challenge to this working group is to develop similar models for the US, where cattle movements are more complex and only partially characterized. To meet this challenge, we have identified a number of cattle movement and TB datasets at both the state and national levels and assembled a group of experts in network and simulation modeling, bovine TB and control and eradication strategies. We will address questions regarding the sources and spread of bovine TB in areas with high local prevalence and at the national scale and how understanding the sources and spread of bovine TB can be used to inform control and eradication strategies. Additionally, we will address how uncertainty in both TB infection status and cattle movement impacts our inference.



deer

Assessment of Risk of Movement and Spread of Bovine Tuberculosis (Mycobacterium bovis) in White-tailed deer and Cattle in Northern Minnesota.


In July 2005, a Minnesota beef herd tested positive for Mycobacterium bovis (M. bovis) and was officially declared infected with bovine tuberculosis.  This was the first infected herd identified since Minnesota ’s Accredited Free status was obtained in 1976. Subsequent testing identified infection in free ranging White-tailed deer and several other cattle herds.  In an effort to minimize the impact of regulatory status to the State and producers, Minnesota initiated the process to establish regulatory zoning to help control the disease.  The goal of this project and subsequent analysis was to determine the risk for spread of M. bovis in both cattle and White-tailed deer populations from the current foci of infection in Northern Minnesota.

Specific objectives of this assessment were to determine if there is sufficient evidence to demonstrate the absence of M. bovis in cattle, White-tailed deer, and other potential hosts in areas of Minnesota considered free of infection.  In addition we evaluated the adequacy of Minnesota’s proposed plan to: a. Prevent the future release of M. bovis from the current foci of infection; and b. The ability to detect potential future introduction of M. bovis into other regions of Minnesota and adjacent states.   The three major risk pathways evaluated for transmission of M. bovis out of the foci of infection were: first  the movement of cattle; second the movement of potentially infected White-tailed deer and other wildlife; and three the movement of potentially M.bovis-contaminated feed and other fomites.

Publications:

PDF (5.2 MB)    Portacci, Katie A; Ryan S. Miller; Mary Ann Bjornsen; Eric Bush; Rodney Howe; Skip Lawrence; Ziad Malaeb. United States Department of Agriculture, Animal Plant Health Inspection Agency. Assessment of Risk Associated with the Minnesota Proposed Plan for Split-state Status for Mycobacterium bovis (bovine tuberculosis). APHIS-2008-0117. 2008.



Deer Hair Loss

Spatially Targeted Surveillance for Deer Hair Loss Syndrome in Columbian black-tailed deer in the Pacific Northwest.


A widespread hair-loss syndrome (HLS) has affected Columbian black-tailed deer in western Oregon and Washington since 1995 and often precedes emaciation, debilitation, pneumonia, and death.  Fawns and does are most often affected by HLS with the highest mortality occurring in fawns.  Apparent prevalence ranges widely but has been reported to be as high as 80% in fawns generating widespread concern over potential implications for populations afflicted.  Two parasites have been implicated in contributing to HLS, a muscle worm known as Parelaphostongylus and an exotic louse species Damalinia (Cervicola).  There has been a perceived spread of the syndrome from Washington state, where it was first identified in 1995, south through western Oregon.  The goals of this project are two fold:  1) identify environmental and ecological variables that might be associated with the presence of Damalinia (Cervicola) and animals with hair loss syndrome; 2) use these associations to identify areas in southern Oregon and northern California where surveillance for Damalinia (Cervicola) should be focused to optimize detection and potentially mitigations.

Publications:

PDF (18 KB) Ryan S. Miller and Jack Mortensen.  Spatially targeted surveillance for deer hair loss syndrome in Columbian black-tailed deer in the Pacific Northwest.  The Wildlife Society 17th Annual COnference. Snowbird,Utah, October 2-6, 2010.



egret

Assessment of Risk for Introduction of Heartwater (Ehrlichia ruminantium) into the Continental United States by Cattle Egrets.


Heartwater, caused by Ehrlichia (formerly Cowdria) ruminantium, is an infectious but non-contagious tick-borne disease of domestic and wild ruminants that often results in death of clinically affected individuals.  This disease was first described in South Africa in 1838 as a nervous condition of sheep following a massive infestation of ticks.  In 2008, many subsaharan Africa countries and Guadeloupe, in the Caribbean islands, reported clinical heartwater in their domestic ruminant livestock populations.  In years past, this disease has also killed livestock on Marie-Galante and Antigua in the Caribbean.

Given the proximity of the U.S. mainland to the Caribbean islands, the ultimate concern for animal health officials, the livestock industry, and other stakeholders may not be what should be done to keep heartwater from being introduced into the continental U.S., but rather what can be done to limit the extent of an outbreak when this incursion occurs.  A key element to controlling the extent of a disease outbreak is early recognition of its presence in an animal population.  Consequently, the objective of this project is to determine the potential risk for introduction for of Ehrlichia ruminantium (Heartwater) into the United States mainland.  A secondary goal of the project is to present the salient features of heartwater to bring increased disease awareness to veterinarians, livestock owners, wildlife biologists, and others.  

Publications:

PDF (290 MB)   Thomas R. Kasari; Ryan S. Miller; Angela M. James; Jerome E. Freier. Assessment of Change in Risk for Release of Ehrlichia ruminantium (Heartwater) into the Continental United States following Discontinuation of the Tropical Bont Tick (Amblyomma variegatum) Eradication Program on St. Croix, U.S. Virgin USDA-APHIS. 2008.

PDF (666 KB)   Thomas R. Kasari; Ryan S. Miller; Angela M. James; Jerome E. Freier. Recognition of the threat of Ehrlichia ruminantium infection in domestic and wild ruminants in the continental United States. Journal of the American Veterinary Medical Association. 237(5) 2010.



goshawk

Determining differences in the spatial distribution of forest structure on the Kaibab Plateau: Implications for forest management and the northern goshawk.


The Kaibab Plateau, in North Central Arizona, has undergone extensive change in the last 100 years due to land management practices such as logging, road building, and fire suppression.  The northern goshawk (Accipiter gentilis), a sensitive species, has been a center of controversy, due to the potential effects of silvicultural practices on goshawk breeding habitat.  Consequently, landscape scale management plans have been proposed for goshawks in both the Pacific Northwest and Desert Southwest. This study investigated possible forest structure differences between the North Kaibab Ranger District and the adjacent Grand Canyon National Park.  Forest inventory data was collected for both the Grand Canyon National Park and North Kaibab Ranger District.  Analysis was conducted at three scales biologically important to the northern goshawk: landscape, stand, and nest site.

Publications:

Miller, Ryan Sanders. Determining differences in the spatial distribution of forest structure on the Kaibab Plateau: Implications for forest management and the northern goshawk. Thesis. Department of Forest Sciences, Colorado State University, 2001.

Acknowledgements:

This project was made possible through a collaborative agreement between Ryan S. Miller and the U.S. Forest Service Rocky Mountain Research Station, specifically Dr. Richard Reynolds and Dr. Suzanne Joy.  Landsat imagery and field equipment was provided by the U.S. Forest Service.   



Farm

Farm Location and Animal Population Simulator:  A system for estimating farm and animal populations.


A significant limitation in developing accurate and meaningful animal disease simulation models in the United States is the lack of data on locations of individual farms and on the numbers and types of animals on each farm.  However, the United States National Agricultural Statistics Service (NASS) Census of Agriculture collects and provides data on numbers of farms and animals by county and postal zip code.  In most cases privacy rules and legislation prevent the distribution of information on individual farms to most federal agencies or the public by NASS.

The Farm Location and Animal Population Simulator generates agriculturally and geographically realistic datasets based on the NASS data for disease simulation models. The simulator uses NASS data to estimate the number and sizes of animal facilities within a geographic region (e.g., states, or counties).  Over the region of interest, geographic constraints are applied so that facilities are not located in urban areas, in lakes, parks, natural areas, or other locations where they are unlikely to occur. Facilities are located randomly, unless a weight matrix is used to concentrate certain types of farms closer to urban areas, live animal markets, and feed suppliers. Numbers of animals are assigned using a distribution.

This simulator is currently being validated with true farm location data for North Carolina and Arkansas.  Validation of the simulator fill be two fold; first the spatial distribution and assignment of animal populations on those farms will be assessed to determine if the patterns are similar to the true distribution of farms and associated populations.  Second, disease spread models will be run on both the true data and the simulated data to determine how simulated population data affects the results of disease spread models.  This project is currently on going.

Publications:

PDF (1.5 MB)   Ryan S. Miller, Kenneth Geter, Barbara Corso, Kim Forde-Folle, Dave Neufeld, Jerry Freier, Janet Russell. Farm Location and Animal Population Simulator: A system for estimating farm and animal populations. 3rd International GISVet Conference. Ersbøll, Annette Kjær; Durr, Peter; Gatrell, Tony : Copenhagen, Denmark, 2007. Web. <www.gisvet.org>.



Crop Duster

Linking the California Pesticide Use Reporting Database with Spatial Land Use Data for Exposure Assessment

In regions of intense agricultural production, the potential for exposure to agricultural pesticides has become an important topic of public health concern. Pesticide transport into watersheds and potential affects on amphibian populations has also become a concern for environmental scientists. The State of California has developed a Pesticide Use Reporting Database (CPUR), with the objective of providing complete pesticide-use data for evaluating possible associations with human illness clusters and potential environmental affects. However, the reporting unit for the database is 1 mi2, which may be too large for accurately predicting exposure at the individual residence level necessary for some epidemiological studies of wildlife and humans.

We used the California Department of Water Resources (CDWR) crop map database to improve the crop location attributes of the CPUR database. We generated exposure metrics based on CPUR alone and CPUR linked to CDWR for birth residences in 1988-1994 in a childhood cancer study conducted by the California Department for Health Services. Sixty-six residences had both CPUR and CDWR data for the child's birth year. We calculated metrics predicting the lbs/mile2 of pesticide for 6 pesticides with high use in the study area: herbicides, simazine and trifluralin; insecticides, dicofol and propargite; and fumigants, methyl bromide and metam sodium. We first compared the exposure classification (exposed / not exposed) to each pesticide and evaluated agreement using a chi-squared test and Cohen's kappa. We then assessed differences in predicted lbs/mile2 of pesticide within a 500-meter buffer around each residence between the metrics, a distance used in previous studies of pesticide exposure.

Four of the six pesticides, simazine, trifluralin, dicofol, and methyle bromide, indicated similar categorical assignment of exposure for each metric. Cohen's kappa values for these pesticides ranged from 0.11 to 0.66. The Wilcoxon signed-rank test indicated significant differences in estimated lbs/mile2 applied within the residential buffers between the CDWR metric and the CPUR metric for 3 of the pesticides. The medians and interquartile ranges were propargite, CDWR = 0.04 (0.00-0.57) and CPUR = 89.41 (14.47-233.69); simazine, CDWR = 0.00 (0.00-0.03) and CPUR = 8.77 (0.00-50.13); methyl bromide, CDWR = 0.00 (0.00-0.00) and CPUR = 0.00 (0.00-342.27). These pesticide exposure metrics are pending field validation but show promise in predicting potential pesticide exposure. Exposure metrics that refine the locational attributes of pesticide use data such as CPUR may reduce exposure misclassification for subjects (wildlife or human) with high or low exposure.

Publications:

PNG (204 KM)   Miller, RS; JR Nuckols; RB Gunier; A Hertz; MH Ward; P Reynolds. Linking the California Pesticide Use Reporting Database with Spatial Land Use Data for Exposure Assessment. International Society of Exposure Analysis 12th conference and International Society for Environmental Epidemiology 14th conference, August 11-15, 2002. Vancouver, British Columbia, Canada.

PDF (1.4 MB)    JR Nuckols; P Reynolds; RS Miller; R Gunier; SJ Weigel; A Hertz; JV Behren.  Final Report: Agricultural chemical exposures and childhood cancer.  National Institute of Health: National Cancer Institute.  Washington DC, Maryland.  March 8, 2002.

PDF (553 KB)    Nuckols, John R; Robert B. Gunier; Philip Riggs; Ryan Miller; Peggy Reynolds; Mary H. Ward. Linkage of the California Pesticide Use Reporting Database with Spatial Land Use for Exposure Assessment. Environmental Health Perspectives 115(5) 2007.

Acknowledgments:

This study was made possible, in part, through a research grant (RO3 CA83071; JR Nuckols, PI) from the National Cancer Institute.  Validation of the metrics is being conducted under research grant (RO1 CA92683; JR Nuckols PI) and through a collaborative project with UC Berkeley (Dr. Pat Buffler), the California Department of Health Services (Dr. Peggy Reynolds), and NCI-Occupational Epidemiology Branch (Dr. Mary H. Ward). We thank Dr. James R. Zumbrunnen, Colorado State University, for his guidance in the statistical analysis of the data.



Crop

Assessing the Spatial Accuracy of the California Pesticide Use Reporting Database for Use in Exposure Assessment Studies


Exposure to agricultural chemicals has been associated with disease outcomes such as cancer, immune system disorders, adverse reproductive outcomes, developmental disorders, and neurological disease in both humans and animals.  In addition, there is evidence that pesticides may severely affect amphibian reproduction and development. Pesticide use data that provides accurate location for where pesticides are applied is important for assessing relationships between disease and pesticide exposure. The State of California has developed a Pesticide Use Reporting Database (CPUR), with the objective of providing complete agricultural pesticide use data for evaluating possible associations with disease in both humans and animals. Several recent epidemiological investigations have utilized the CPUR database. However, the spatial accuracy of the database has not been evaluated. The CPUR database was established in the 1950's with limited reporting and contains information on the pesticide type, pounds applied, date, method of application, acres of crop treated. Beginning in 1990, a full use reporting system was instituted requiring commercial growers to report all pesticides used in agriculture. The reporting unit for the database is Public Land Survey System Section, which is approximately 1 mi2.

We compared the CPUR pesticide application data by crop with high precision, 100% ground verified land-use data collected by the California Department of Water Resources (CDWR). CDWR identifies 83 specific crop types with a minimum mapping unit of 0.003 mi2. We used a Geographic Information System (GIS), to conduct a comparative analysis of the location of pesticide application by crop, as reported in CPUR, with the location of the same crops in the CDWR database. We conducted the comparative analysis for ten crops with the greatest number of pesticide applications for two counties, San Joaquin (1988) and Kings (1991). To assess the accuracy of the CPUR data, we developed a GIS analytical procedure, which computed the spatial agreement between the two datasets. The comparative analysis was performed at the Section extent (N = 3,856). We tested the resulting congruence estimates for statistical significance using a one-sided binomial test for two levels of assumed crop location error in the CDWR database (1% and 5% error).

Overall agreement between CPUR and CDWR was relatively high, although statistically significant differences existed between the datasets assuming 5% error in CDWR data. Accuracy assessment indicates large variation in CPUR reporting accuracy, ranging from 73.1% for cherries to 95.1% for cotton. In general, overall agreement was significantly higher in Kings County for 1991 than for San Joaquin County in 1988 for both non-permanent crops (92.9% vs 81.9% respectively) and semi-permanent crops (87.4% vs 80.7% respectively). These results indicate spatial and temporal differences in accuracy of the CPUR dataset, at both the aggregate and individual crop level. The spatial accuracy of pesticide-use data can affect exposure assessment, and may result in misclassification of exposure in epidemiological investigations of wildlife (amphibians) or humans.

Publications:

PNG (195 KB)   Miller, RS; JR Nuckols; R Gunier; A Hertz; P Reynolds. Assessing the Spatial Accuracy of the California Pesticide Use Reporting Database for Use in Exposure Assessment Studies. International Society of Exposure Analysis 12th conference and International Society for Environmental Epidemiology 14th conference, August 11-15, 2002. Vancouver, British Columbia, Canada.

PDF (5.3 MB)   Stephanie, JW; JR Nuckols; CC Skinner; RS Miller.  Final report on the accuracy and feasibility of using spatial data to refine the California pesticide use data set.  Technical Report, California Department of Health Services.  May 28, 1999.

Acknowledgments:

This study was made possible, in part, through a research grant (RO3 CA83071; JR Nuckols, PI) from the National Cancer Institute.  Research is continuing under research grant (RO1 CA92683; JR Nuckols PI) and through a collaborative project with UC Berkeley (Dr. Pat Buffler), the California Department of Health Services (Dr. Peggy Reynolds), and NCI-Occupational Epidemiology Branch (Dr. Mary H. Ward). We thank Dr. James R. Zumbrunnen, Colorado State University, for his guidance in the statistical analysis of the data.



pest

Identifying Populations Potentially Exposed to Agricultural Pesticides Using Remote Sensing and a Geographic Information System


Pesticides used in agriculture may cause adverse health effects among human and wildlife populations living near agricultural areas. However, identifying populations most likely to be exposed is difficult. We conducted a feasibility study to determine whether satellite imagery could be used to reconstruct historical crop patterns. We used historical Farm Service Agency records as a source of ground reference data to classify a late summer 1984 satellite image into crop species in a three-county area in south central Nebraska. Residences from a population-based epidemiologic study of non-Hodgkin lymphoma were located on the crop maps using a geographic information system (GIS). Corn, soybeans, sorghum, and alfalfa were the major crops grown in the study area.

Eighty-five percent of residences could be located, and of these 22% had one of the four major crops within 500 meters of the residence, an intermediate distance for the range of drift effects from pesticides applied in agriculture. We determined the proximity of residences to specific crop species and calculated crop-specific probabilities of pesticide use based on available data. This feasibility study demonstrated that remote sensing data and historical records on crop location can be used to create historical crop maps. The crop pesticides that were likely to have been applied can be estimated when information about crop-specific pesticide use is available. Using a GIS, zones of potential exposure to agricultural pesticides and proximity measures can be determined for residences in a study.

Publications:

PDF (1.2 MB)   Ward, MH; JR Nuckols; SJ Weigel; SK Maxwell; KP Cantor; RS Miller. Identifying Populations Potentially Exposed to Agricultural Pesticides Using Remote Sensing and a Geographic Information System. Environmental Health Perspectives. 108:5-12; 2000.

Acknowledgements:

We acknowledge the support and cooperation of the Nebraska State Farm Service Agency (M. Bowen, Director) and all of the individual county agencies and their staffs who helped with the ground reference information, especially B. McDermott and the Hall County Farm Service Agency staff.  This project was partly made possible through the support of the National Cancer Institute subcontract NO2-CP-71100.