Work

Demonstrating true disease freedom distinct from low prevalence across time: A zero inflated model with disease introduction and spread considerations

Year: 2026

Type: article

Abstract: International standards guide claims of disease freedom status, supported by surveillance-based evidence of disease absence through time. Conventional methods for assessing absence have trouble distinguishing between low (below a detection threshold) and zero prevalence of disease. Current methods addressing this limitation lack the ability to incorporate historical data and propagate evidence of absence through time when there is potential for disease introduction. Further, maintenance across time requires continuous assurance which is supported by incorporating historical data and disease dynamics. Our new model framework, Zero-Inflated Prevalence for FREEdom over Time (ZIP-FREE-T), is a Bayesian model that (1) includes zero-inflated beta prevalence distributions affording probability computation at any threshold prevalence whether zero (absolute absence) or non-zero (effective absence), (2) infers the effect of a previously missed infection using spread dynamics, and (3) incorporates introduction risk addressing both the probability and magnitude of an introduction event. We apply our model to evaluate sample sizes needed to maintain assurance of disease freedom from Perkinsus marinus in a hypothetical population of the oyster Crassostrea virginica. Sensitivity analysis for this example suggests specified prior distributions and spread rates are non-ignorable. Solutions offered by ZIP-FREE-T bring awareness to, and allow discussion and planning around, issues central to population health management. These include the probability of zero rather than low prevalence, the potential for disease introduction and subsequent spread, as well as the effect of risk mitigation on the assurance of disease freedom.

Source: Preventive Veterinary Medicine

DOI: 10.1016/j.prevetmed.2026.106892

Authors: Clark Kogan, Travis Galoppo, Leonid Kalachev, Lori Gustafson, Marta Remmenga

Institutions: Washington State University Spokane, University of Montana, Animal and Plant Health Inspection Service, United States Department of Agriculture, Center for Epidemiology and Animal Health

Language: English

Topic: Animal Disease Management and Epidemiology

Subfield: Agronomy and Crop Science

Field: Agricultural and Biological Sciences

Domain: Life Sciences

SDG: Good health and well-being

Open Access status: hybrid

Estimated APC paid: $3,280