Modelling of strategies for genetic control of scrapie in sheep: The importance of population structure

• Published in: PloS one 2018-03, Vol.13 (3), p.e0195009-e0195009
• Main Authors: Hagenaars, Thomas J, Melchior, Marielle B, Windig, Jack J, Bossers, Alex, Davidse, Aart, van Zijderveld, Fred G
• Format: Article
• Language: English
• Subjects: Animal breeding; Animal Breeding & Genomics; Animal Breeding and Genetics; Animal populations; Animals; Bacteriologie & Epidemiologie; Bacteriology & Epidemiology; Biological research; Biology and Life Sciences; Bovine spongiform encephalopathy; Breeding; BSE; Compliance; CVI Bacteriologie en Epidemiologie; CVI Bacteriology and Epidemiology; CVI Infectiebiologie; CVI Infection Biology; CVI onderzoek; Disease control; Disease resistance; Encephalopathy; Epidemiology; Fokkerij & Genomica; Fokkerij en Genetica; Genetic aspects; Genetic control; Genotypes; Heterogeneity; Immunization; Infectiebiologie; Infection Biology; Infection control; Infections; Infectious diseases; Innovations; Livestock; LR - Animal Breeding & Genomics; LR - Genomica; Mathematical models; Medicine and Health Sciences; Onderzoek; Parameter estimation; Parameters; People and places; Population; Population structure; Prevention; Rams; Research and Analysis Methods; Scrapie; Sheep; Spongiform encephalopathy; Surveillance; Transmissible spongiform encephalopathy; Veterinary medicine; WIAS
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0195009

Scrapie is a transmissible spongiform encephalopathy in sheep and an example of a disease that may be controlled through breeding for disease resistance. Member states of the European Union have introduced strategies for breeding against scrapie based on the selection of genetically resistant breeding rams. An ambitious strategy adopted in The Netherlands consisted of selecting resistant rams for breeding throughout both breeding and production sectors. Mathematical modelling of the effect of a breeding program on the spreading capacity of scrapie in a national flock is needed for making assessments on how long a breeding strategy needs to be maintained to achieve disease control. Here we describe such a model applied to the Dutch situation, with the use of data on the genetic content of the Dutch sheep population as well as on scrapie occurrence in this population. We show that the time needed for obtaining scrapie control depends crucially on two parameters measuring sheep population structure: the between-flock heterogeneity in genotype frequencies, and the heterogeneity of mixing (contact rates) between sheep flocks. Estimating the first parameter from Dutch genetic survey data and assuming scenario values for the second one, enables model prediction of the time needed to achieve scrapie control in The Netherlands.