title: Modelling the within-herd transmission ofMycoplasma hyopneumoniaein closed pig herds.
abstract: BACKGROUND
  A discrete time, stochastic, compartmental model simulating the spread ofMycoplasma hyopneumoniaewithin a batch of industrially raised pigs was developed to understand infection dynamics and to assess the impact of a range of husbandry practices. A 'disease severity' index was calculated based on the ratio between the cumulative numbers of acutely and chronically diseased and infectious pigs per day in each age category, divided by the length of time that pigs spent in this age category. This is equal to the number of pigs per day, either acutely or chronically infectious and diseased, divided by the number of all pigs per all days in the model. The impact of risk and protective factors at batch level was examined by adjusting 'acclimatisation of gilts', 'length of suckling period', 'vaccination of suckling pigs againstM. hyopneumoniae', 'contact between fattening pigs of different age during restocking of compartments' and 'co-infections in fattening pigs'.
  
  
  RESULTS
  The highest 'disease severity' was predicted, when gilts do not have contact with live animals during their acclimatisation, suckling period is 28 days, no vaccine is applied, fatteners have contact with pigs of other ages and are suffering from co-infections. Pigs in this scenario become diseased/infectious for 26.1 % of their lifetime. Logistic regression showed that vaccination of suckling pigs was influential for 'disease severity' in growers and finishers, but not in suckling and nursery pigs. Lack of contact between gilts and other live pigs during the acclimatisation significantly influenced the 'disease severity' in suckling pigs but had less impact in growing and finishing pigs. The length of the suckling period equally affected the severity of the disease in all age groups with the strongest association in nursery pigs. The contact between fatteners of different groups influenced the course of infection among finishers, but not among other pigs. Finally, presence of co-infections was relevant in growers and finishers, but not in younger pigs.
  
  
  CONCLUSIONS
  The developed model allows comparison of different prevention programmes and strategies for controlling transmission ofM. hyopneumoniae.
authors.affiliation: Veterinary Epidemiology, Economics and Public Health Group, Royal Veterinary College London, Hawkshead Lane, Hatfield, Hertfordshire AL97TA UK.|Clinic for Swine, Vetsuisse Faculty, University of Berne, Bremgartenstrasse 109a, 3012 Bern, Switzerland.
authors.forename: Heiko
authors.initials: H
authors.lastname: Nathues
authors.affiliation: Veterinary Epidemiology, Economics and Public Health Group, Royal Veterinary College London, Hawkshead Lane, Hatfield, Hertfordshire AL97TA UK.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Fournie
authors.affiliation: International Livestock Research Institute, Addis Ababa, Ethiopia.
authors.forename: Barbara
authors.initials: B
authors.lastname: Wieland
authors.affiliation: Veterinary Epidemiology, Economics and Public Health Group, Royal Veterinary College London, Hawkshead Lane, Hatfield, Hertfordshire AL97TA UK.
authors.forename: Dirk U
authors.initials: DU
authors.lastname: Pfeiffer
authors.affiliation: Veterinary Epidemiology, Economics and Public Health Group, Royal Veterinary College London, Hawkshead Lane, Hatfield, Hertfordshire AL97TA UK.
authors.forename: Katharina D C
authors.initials: KDC
authors.lastname: Stärk
keywords: Enzootic pneumonia; Epidemiology; Infectious disease; Prevention