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ARS Home » Southeast Area » Athens, Georgia » U.S. National Poultry Research Center » Avian Disease and Oncology Research » Research » Publications at this Location » Publication #314371
Title: An observational study of the temporal and spatial patterns of Marek's-disease-associated leukosis condemnation of young chickens in the United States of America

Author
item KENNEDY, DAVID - Pennsylvania State University
item Dunn, John
item DUNN, PATTY - Pennsylvania State University
item READ, ANDREW - Pennsylvania State University

Submitted to: Preventive Veterinary Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2015
Publication Date: 7/1/2015
Citation: Kennedy, D.A., Dunn, J.R., Dunn, P.A., Read, A.F. 2015. An observational study of the temporal and spatial patterns of Marek's-disease-associated leukosis condemnation of young chickens in the United States of America. Preventive Veterinary Medicine. 120(3-4):328-335. doi:10.1016/j.prevetmed.2015.04.013.

Interpretive Summary: Marek's disease, a disease primarily affecting immature chickens, is a worldwide problem that has on at least three occasions threatened the poultry industry in the United States. A rich dataset to study the occurrence of this disease is available because USDA has required mandatory inspections of all commercially sold poultry of significant scale since the mid-20th century with over 99% of all chickens inspected. We confirmed previous findings that there are differences in Marek’s disease condemnation rates between states, across years, and within years. The patterns we found also suggest that locally shared farm practices, virus transmission between farms, or viral persistence may be important to understanding the dynamics of the disease. These observations will help shape disease prevention strategies.

Technical Abstract: Marek's disease, a disease primarily affecting immature chickens, is a worldwide problem that has on at least three occasions threatened the poultry industry in the United States. A rich dataset to study the epidemiology of this disease is available because the United States Department of Agriculture has required mandatory inspections of all commercially sold poultry of significant scale since the mid-20th century with over 99% of all chickens inspected. This dataset includes monthly totals aggregated by state since 1961 of the number of ''young chickens'' inspected and the number with "leukosis", a condemnation category that is almost always associated with Marek's disease in this category of birds. The objective of this study was to analyze temporal and spatial patterns in this condemnation data to gain insight into the ecology and epidemiology of the causative virus. We extracted visual patterns in the data using seasonal trend decomposition, and we tested for statistical significance using extended linear modeling techniques. The analysis confirmed previous findings that there are differences in leukosis condemnation rates between states, across years, and within years. The analysis also revealed several patterns not previously highlighted, including spatial and temporal autocorrelations in leukosis condemnation, changes to the amplitude of seasonality over time, and increasing within-year variation in condemnation rate over time. These patterns suggest that locally shared farm practices, virus transmission between farms, or viral persistence may be important to understanding the dynamics of the disease. We also discuss the plausibility of other potential explanations for these patterns.