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INVESTIGATOR: Mitchell, R. M.; Schukken, Y. H.; Medley, G. F.

PERFORMING INSTITUTION:
CORNELL UNIVERSITY
ITHACA, NEW YORK 14853

MODELING TRANSMISSION DYNAMICS OF MYCOBACTERIUM AVIUM SUBSP. PARATUBERCULOSIS TO IMPROVE CONTROL STRATEGIES ON COMMERCIAL U.S. DAIRY FARMS

NON-TECHNICAL SUMMARY: Mycobacterium avium subspecies paratuberculosis (MAP) is a chronic infection of cows and sheep which is common to most dairy farms in the United States (68% in the most recent national survey). Animals usually do not test positive for MAP until they are adults, even though we believe the majority of animals are infected at a very young age. Clinical disease causes progressive diarrhea, wasting and decrease in milk production in dairy cattle. Understanding MAP transmission cycles allows us to better design control strategies which are cost effective for farmers. In this project, a seven-year longitudinal dataset of samples from three northeastern US dairy farms will be analyzed to better understand how MAP is being transmitted between animals on the farms. We will look for associations between exposure to highly infectious adult animals and becoming infected: calves from infected dams, clusters of infected animals that were born on the same date, animals exposed to highly infectious animals as adults. We will test whether animals are commonly infected with more than one MAP strain (simulataneously, or throughout life) by testing composite samples from individual animals via dilution. This method will also be used to determine MAP diversity in positive environmental samples. Currently we assume that most farms have one strain of MAP on the farm, or that there is no competition between MAP strains. However, this project will be the first to examine long-term dynamics of MAP on farms with multiple strains present at the strain level. Based on the findings from the longitudinal dataset, we will construct mathematical models of MAP transmission that allow us to trace individual animals and assign duration of infection along specific distributions. Findings from this work will be disseminated in both scientific papers and meetings. These findings will aid veterinarians in advising farmers on best management practices to decrease clinical disease on US dairy farms.

OBJECTIVES: The overall goal of this project is to develop a mathematical model using precise longitudinal field and molecular typing data that will explain endemic persistence of MAP within dairy herds and allows evaluation of cost-effective MAP control strategies. To reach this long term goal, the following three specific objectives are defined: (1) Develop an expanded state transition model, accommodating new insights in infection transmission and latency to analyze a longitudinal dataset gathered by the Regional Dairy Quality Management Alliance and Johne's Disease Integrated Project. (2) Accurately estimate infection transmission parameters using molecular epidemiology and longitudinal field data. (3) Develop a stochastic, individual-based, model of infection transmission of MAP. This model is expected to more accurately predict infection endemicity and is suitable for development of MAP control programs. Findings from this work will be disseminated both in scientific literature and by short courses. Target date for completing analysis of MAP transmission at birth is June 2012. Target date for completing work on potential adult-to-adult transmission is early 2013, and final paper on MAP endemicity is June 2013. A short course on use of mathematical models for bovine veterinarians will be developed for Fall 2012 and a semester course for veterinary students will be proposed for Spring 2013.