title: Adaptive Test Schemes for Control of Paratuberculosis in Dairy Cows.
abstract: Paratuberculosis is a chronic infection that in dairy cattle causes reduced milk yield, weight loss, and ultimately fatal diarrhea. Subclinical animals can excrete bacteria (Mycobacterium avium ssp. paratuberculosis, MAP) in feces and infect other animals. Farmers identify the infectious animals through a variety of test-strategies, but are challenged by the lack of perfect tests. Frequent testing increases the sensitivity but the costs of testing are a cause of concern for farmers. Here, we used a herd simulation model using milk ELISA tests to evaluate the epidemiological and economic consequences of continuously adapting the sampling interval in response to the estimated true prevalence in the herd. The key results were that the true prevalence was greatly affected by the hygiene level and to some extent by the test-frequency. Furthermore, the choice of prevalence that will be tolerated in a control scenario had a major impact on the true prevalence in the normal hygiene setting, but less so when the hygiene was poor. The net revenue is not greatly affected by the test-strategy, because of the general variation in net revenues between farms. An exception to this is the low hygiene herd, where frequent testing results in lower revenue. When we look at the probability of eradication, then it is correlated with the testing frequency and the target prevalence during the control phase. The probability of eradication is low in the low hygiene herd, and a test-and-cull strategy should probably not be the primary strategy in this herd. Based on this study we suggest that, in order to control MAP, the standard Danish dairy farm should use an adaptive strategy where a short sampling interval of three months is used when the estimated true prevalence is above 1%, and otherwise use a long sampling interval of one year.
authors.affiliation: DTU VET, Section for Epidemiology, Technical University of Denmark, Denmark.
authors.forename: Carsten
authors.identifier: http://orcid.org/0000-0001-9292-5526
authors.initials: C
authors.lastname: Kirkeby
authors.affiliation: DTU VET, Section for Epidemiology, Technical University of Denmark, Denmark.
authors.forename: Kaare
authors.initials: K
authors.lastname: Græsbøll
authors.affiliation: Department of Large Animal Sciences, Section for Animal Welfare and Disease Control, University of Copenhagen, Denmark.
authors.forename: Søren Saxmose
authors.initials: SS
authors.lastname: Nielsen
authors.affiliation: DTU Compute, Section for Dynamical Systems, Department of Applied Mathematics and Computer Science, Technical University of Denmark, Richard Petersens Plads, Denmark.
authors.forename: Lasse Engbo
authors.initials: LE
authors.lastname: Christiansen
authors.affiliation: DTU VET, Section for Epidemiology, Technical University of Denmark, Denmark.
authors.forename: Nils
authors.initials: N
authors.lastname: Toft
authors.affiliation: DTU VET, Section for Epidemiology, Technical University of Denmark, Denmark.
authors.forename: Tariq
authors.initials: T
authors.lastname: Halasa
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000175:diagnosis* / Q000453:epidemiology / Q000517:prevention & control*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006920:Hygiene; D053208:Kaplan-Meier Estimate; D016927:Mycobacterium avium subsp. paratuberculosis; D010283:Paratuberculosis / Q000175:diagnosis* / Q000453:epidemiology / Q000517:prevention & control*; D015995:Prevalence; D012680:Sensitivity and Specificity