Genetic management strategies for controlling infectious diseases in livestock populations

SC Bishop*, KA MacKenzie

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

This paper considers the use of disease resistance genes to control the transmission of infection through an animal population. Transmission is summarised by R-0, the basic reproductive ratio of a pathogen. If R-0 > 1.0 a major epidemic can occur, thus a disease control strategy should aim to reduce R-0 below 1.0, e.g. by mixing resistant with susceptible wild-type animals. Suppose there is a resistance allele, such that transmission of infection through a population homozygous for this allele will be R-02 <R-01, where R-01 describes transmission in the wildtype population. For an otherwise homogeneous population comprising animals of these two groups, R-0 is the weighted average of the two sub-populations: R-0 = R-01ρ + R-02 (1 - ρ), where p is the proportion of wildtype animals. If R-01 > 1 and R-02 <1, the proportions of the two genotypes should be such that R-0 &LE; 1, i.e. ρ &LE; (R-0 - R-02)/(R-01 - R-02)- If R-02 = 0, the proportion of resistant animals must be at least 1 - 1/R-01. For an n genotype model the requirement is still to have R-0 &LE; 1.0. Probabilities of epidemics in genetically mixed populations conditional upon the presence of a single infected animal were derived. The probability of no epidemic is always 1/(R-0 + 1). When R-0 <1 the probability of a minor epidemic, which dies out without intervention, is R-0/(R-0 + 1). When R-0 > 1 the probability of a minor and major epidemics are 1/(R-0 + 1) and (R-0 - 1)/(R-0 + 1). Wherever possible a combination of genotypes should be used to minimise the invasion possibilities of pathogens that have mutated to overcome the effects of specific resistance alleles.

Original languageEnglish
Pages (from-to)S3-S17
Number of pages15
JournalGenetics Selection Evolution
Volume35
DOIs
Publication statusPublished - 2003
Event2nd International Symposium on Candidate Genes for Animal Health - MONTPELLIER, France
Duration: 16 Aug 200218 Aug 2002

Keywords

  • genetics
  • epidemiology
  • disease resistance
  • livestock
  • R-0
  • QUANTITATIVE TRAIT LOCI
  • RESISTANCE
  • MODELS
  • HETEROGENEITY
  • COMPUTATION
  • SELECTION
  • QUANTIFY
  • PRESSURE
  • DYNAMICS
  • SCRAPIE

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