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Emerging and Re-emerging Zoonotic Diseases

Investigators
Saif, Yehia; LeJeune, Jeffrey; Rajashekara, Gireesh
Institutions
Ohio State University
Start date
2008
End date
2013
Objective
The primary goal of this research is to exploit the research expertise of the Food Animal Health Research Program to enhance the understanding of the microbiology, epidemiology and pathogenesis and control of infectious agents of livestock that have potential for zoonotic transmission, including several pathogens that may be used as agents of agribioterrorism.

To achieve this goal we propose to investigate the following aspects of zoonotic agents harbored by food-producing animals:

  1. Mechanisms of microbial pathogenesis of zoonotic agents of food safety concerns including the production of bacterial toxins
  2. Immune response using animal models of infection and immunity
  3. Epidemiology and natural history of infection and interspecies transmission of zoonotic pathogens
  4. Development of vaccines, therapeutics, adjuvants, and diagnostics for food safety and agribiodefense.
More information
NON-TECHNICAL SUMMARY: Diseases transmitted through food borne/waterborne routes, constitute a significant burden for public health. Over two-thirds of all infectious agents affecting humans have animal reservoir. Importantly, treatment of diseases caused food/waterborne microbes is complicated either by the emergence of resistant bacteria or lack of effective treatments available for viruses. These public health and safety concerns underscore the critical need for integrated research efforts to better understand the ecology, epidemiology and pathogenesis of disease that are communicable to humans through food animals and water, so that effective strategies can be developed to prevent the dissemination of these organisms in the environment and limit the spread of these agents to humans. The over all goal of this project is to understand the epidemiology, ecology and pathogenesis of medically important infectious agents in animal reservoirs and the environment including; investigation of the occurrence, dissemination and ecological fitness of antibiotic resistant pathogens; and design of efficient methods/strategies and models for the detection and prevention of pathogens that are communicable to humans.

APPROACH: Clearly, due to the wide variety of zoonotic pathogens that may emerge as potential public health threats, the specific methods will vary from individual project to project. However, our underlying strategy is to use a hypothesis-driven research approach to provide sound scientific data concerning the research problems investigated. Research may include development and/or utilization of animal models of infection to characterize mechanisms of pathogenesis and pathogen/host interactions. These include studies of pathogenesis and comparative pathogenesis, interspecies transmission of pathogens, understanding the molecular basis of pathogenesis, studies of pathogen and host gene expression and characterization of host genetic risk factors for disease susceptibility. We will exploit current advances in the detection of gene and protein expression patterns to assess disease progression, and to seek unique host cellular signatures indicative of infection and/or protective immune responses. Studies of the natural rates of horizontal gene transfer, especially of plasmid-encoded toxins and resistance factors, in the microbial ecosystems likely to be most exposed to agents of agribioterrorism For the studies of natural history of microbial pathogens and epidemiology of infections in natural non-human and human hosts, we will use extensive in-field sampling strategies coupled with epidemiological practices targeted at identifying factors that influence the distribution, acquisition, course and severity of human disease. This will also include studies on pathogens in the environment and non-food-producing vectors, when those studies may contribute to the understanding of factors bearing on emergence, transmission, persistence, development of virulence, host switching, and/or epidemic/epizootiologic thresholds as they directly pertain to human disease.

PROGRESS: 2007/01 TO 2007/12
OUTPUTS: Multi-disciplinary (Food Science, Veterinary Medicine, Bacterial Ecology, Plant Pathology, Horticulture and Crop Science, Human Behavoir, etc) teams were formed to address complex issues continually emerging in food safety. Activities included not only laboratory and field studies to achieve the stated goals, but also undergraduate, graduate, and professional teaching, graduate student mentoring and outreach events including workshops, symposia, and conference presentations.
PARTICIPANTS: Individuals: LeJeune, J. T.; Saif, Y. M.; Saif, L.; Jackwood, D.; Theil, K. Kauffman, MD, Partner Organizations: Ohio Depts of Health and Ag Training or professional development:Graduate students: Dan Aruscavage, Sanja Ilic, Alex Rodriguez, Ann Kersting.
TARGET AUDIENCES: Veterinarians. Public Health Officals and Agencies. Food Producers: livestoch and vegetable and fruit growers. Research Scientists: Health, Evironment. Public.
PROJECT MODIFICATIONS: None

IMPACT: 2007/01 TO 2007/12
Pathogens that contaminate the food supply have been better characterized. Specifically, these studies provide insight in to the emergence and evolution of pathogens in the food chain. For example, we have identified that antibiotic resistance genes may be transferred by bacteriophage among strains of Salmonella, that not Escherichia coli O157 are of equal pathogenic potential, and that management factors (antibiotic use, stocking density) on farms may impact the prevalence of Salmonella in pigs. In addition the distribution of pathogenic organisms in wildlife was reported

PROGRESS: 2006/01/01 TO 2006/12/31
Objectives 1) Mechanisms of microbial pathogenesis of zoonotic agents, including the production of bacterial toxins 2) Immune Response using animal models of infection and immunity; 3) Epidemiology and natural history of infection; 4) Development of vaccines, therapeutics, adjuvants, and diagnostics for food safety and Biodefense. Both field studies and laboratory experiments have been conducted and are ongoing to achieve these aims. One study considered gene location within bacteria as a function of genetic element mobility. Our emphasis is on prophage encoding of bacterial virulence factors (VFs). At least four mechanisms potentially contribute to phage encoding of bacterial VFs: (i) Enhanced gene mobility; (ii) Epistatic interactions; (iii) Phage could amplify VFs during disease progression; and finally (iv) phage-encoded VFs could enhance phage Darwinian fitness, particularly by acting as ecosystem-modifying agents. Pathogens on edible plants present a significant potential source of human illness. From 1991 to 2002, 21% of Escherichia coli O157:H7 outbreaks were from produce-related sources. E. coliO157and other enteric bacteria can contaminate the surface of edible plants both pre- and postharvest. Some pathogens do not survive on the leaf surface or are removed by washing, but a significant portion of these enteric pathogens can persist on the surface and proliferate. Proliferation of these dangerous pathogens can increase the likelihood of foodborne disease associated with fresh or minimally processed produce. Several intrinsic and extrinsic factors determine the ability of enteric pathogens to attach and proliferate in the phyllosphere of plants. These include motility of the pathogen, leaching of nutrients by the plant, and interaction with epiphytic organisms. The interaction of enteric pathogens with the environment can lead to internalization into tissue, incorporation into biofilms, and genetic transfer. Current produce sanitation practices can reduce the microbial load from1 log10 to 3 log10, so there are many new treatments possible. Understanding the ecology of enteric pathogens on plants is important to the development of sanitation methods and biocontrol agents. This knowledge can also assist the farmer in preventing contamination. With increasing consumption and importation of produce, its safety is a high priority for processors and U.S. consumers. Food safety may be markedly improved with proper attention to pathogens on edible plants.

IMPACT: 2006/01/01 TO 2006/12/31
Understanding the underlying microbiological and ecological factors driving the emergence and persistence of foodborne pathogens has provided targeted direction for applied research projects that address these principles.

PROGRESS: 2005/01/01 TO 2005/12/31
Controlled studies have elucidated the primary factors influencing the dissemination of Shiga-toxin encoding phages from E. coli O157. We have begun to test several commonly used therapeutic antibiotics (Micotil, Nuflor, Baytril, Naxcel, and Tetracycline) on their ability to induce phage in vitro. The positive control treatment (not shown in figure) with mitomycin C resulted in approximately 20x increase. Similar results were observed regardless of whether or not bile salts were included in the test medium. Again these results are still preliminary and statistical analysis has not been conducted to determine significance of differences between treatments, however, results suggest (see figure) that at minimum inhibitory concentration of each antibiotic, these agents induce phage release only marginally, if at all. In order to more precisely predict food safety risks, the fecal presence of foodborne pathogens among animals at slaughter must be correctly determined. Quantification of E. coli O157 is also desirable. In two separate experiments, detection and enumeration of a nalidixic acid resistant strain of E. coli O157 in bovine feces was assessed by culture on MacConkey agar supplemented with nalidixic acid (MACnal) and compared to overnight broth enrichment followed by immunomagnetic separation (IMS) and to direct plating (DP) of dilutions of bovine feces onto Sorbitol MacConkey agar containing cefixime and tellurite (SMACct). The sensitivity of detection of E. coli O157 by both DP and IMS was highly dependent upon the initial concentration of the target organism in the sample. Sensitivity of detection by IMS was poor below 100 CFU/g, but was better, and not affected by initial E. coli O157 numbers, above this concentration. Sensitivity of detection of E. coli O157 in bovine feces at low initial concentrations is very poor for both direct plating and IMS. Direct plating of dilutions of bovine feces on SMACct can be used to determine the magnitude of fecal E. coli excretion among cattle excreting greater than 100 CFU/g. Among positive samples identified by direct plating on SMACct, the direct counts of E. coli O157:H7 were highly correlated with the estimates obtained on the MACnal plates (r = 0.88, P<0.001). Because the majority of cattle excrete less than 102 CFU E. coli O157/g feces, most studies, including those using IMS methods, probably grossly underestimate the prevalence of E. coli O157 in cattle.

IMPACT: 2005/01/01 TO 2005/12/31
The cause of the emergence of E. coli O157 as an important human pathogen remains enigmatic. The data presented in our study suggest that the use of therapeutic antibiotics in cattle contributes minimally to the release of stx-encoding phages and therefore has little impact on the emergence of novel Shiga toxin-producing E. coli strains. Our comparison of diagnostic assays is important because it demonstrates that direct plating for E. coli O157 can give reliable information about the prevalence of the organism in bovine feces. This direct plating assay, when used in pre-harvest food safety experiments will allow for the inexpensive, yet qualitative, assessment of E. coli in bovine feces, information that is critically needed to fill gaps in quantitative risk assessment models related to food and environmental safety.

PROGRESS: 2004/01/01 TO 2004/12/31
Progress: Objectives 1) Mechanisms of microbial pathogenesis of zoonotic agents, including the production of bacterial toxins 2) Immune Response using animal models of infection and immunity; 3) Epidemiology and natural history of infection; 4) Development of vaccines, therapeutics, adjuvants, and diagnostics for food safety and Biodefense. Both field studies and laboratory experiments have been conducted and are ongoing to achieve these aims. Controlled studies have elucidated the primary factors influencing the magnitude of Shiga-toxin production from E. coli O157. The immune response to enteric viruses and virus-like particles continues to be evaluated in gnotobiotic piglet model of human disease. Initial information is now available on the global distribution of pathogenic strains of E. coli O157, as well as farm-to-farm variability of Mycobacterium paratuberculosis strains, including isolates obtained from human cases of Crohn's Disease.

IMPACT: 2004/01/01 TO 2004/12/31
Better diagnostic tools are now available for the characterization of E. coli O157:H7 and Mycobacterium avaium subsp. paratuberculosis. These test will be available to all researchers to expedite further research and understanding of these important bacterial agents

PROGRESS: 2003/01/01 TO 2003/12/31
Objectives 1. Mechanisms of microbial pathogenesis of zoonotic agents, including the production of bacterial toxins 2. Immune Response using animal models of infection and immunity 3. Epidemiology and natural history of infection 4. Development of vaccines, therapeutics, adjuvants, and diagnostics for food safety and biodefense Research has progressed in all objectives. Many projects encompass all objectives. For example the identification of a novel target for the identification of pathogenic Shiga toxin-producing E. coli has led to a greater understanding of the mechanisms of pathogenesis and the epidemiology of this pathogen in human and animal populations. Likewise, given the uncertainty of zoonotic potential of Mycobacterium avaium subsp. paratuberculosis, work has also been conducted on this organism. The potential for the cross-species transmission of M. avium paratuberculois and the relation ship between M. avium paratuberculois can now be determined. This information is critical in understanding the natural history of Johnes disease and the possible relationship of this agent in the etiologic of Chrones disease. Expected impact Better diagnostic tools are now available for the characterization of E. coli O157:H7 and Mycobacterium avaium subsp. paratuberculosis. These test will be available to all researchers to expedite further research and understanding of these important bacterial agents.

IMPACT: 2003/01/01 TO 2003/12/31
Better diagnostic tools are now available for the characterization of E. coli O157:H7 and Mycobacterium avaium subsp. paratuberculosis. These test will be available to all researchers to expedite further research and understanding of these important bacterial agents

Funding Source
Nat'l. Inst. of Food and Agriculture
Project source
View this project
Project number
OHO00003-AH
Accession number
196668
Categories
Bacterial Pathogens
Natural Toxins
Sanitation and Quality Standards
Escherichia coli
Viruses and Prions