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  • Methodology
  • Open Access

Genetic management strategies for controlling infectious diseases in livestock populations

Genetics Selection Evolution200335 (Suppl 1) :S3

https://doi.org/10.1186/1297-9686-35-S1-S3

  • Accepted: 4 February 2003
  • Published:

Abstract

This paper considers the use of disease resistance genes to control the transmission of infection through an animal population. Transmission is summarised by R0, the basic reproductive ratio of a pathogen. If R0 > 1.0 a major epidemic can occur, thus a disease control strategy should aim to reduce R0 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 R02 < R01, where R01 describes transmission in the wildtype population. For an otherwise homogeneous population comprising animals of these two groups, R0 is the weighted average of the two sub-populations: R0 = R01ρ+ R02 (1 - ρ), where ρ is the proportion of wildtype animals. If R01 > 1 and R02 < 1, the proportions of the two genotypes should be such that R0 ≤ 1, i.e. ρ ≤ (R0 - R02)/(R01 - R02). If R02 = 0, the proportion of resistant animals must be at least 1 - 1/R01. For an n genotype model the requirement is still to have R0 ≤ 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/(R0 + 1). When R0 ≤ 1 the probability of a minor epidemic, which dies out without intervention, is R0/(R0 + 1). When R0 > 1 the probability of a minor and major epidemics are 1/(R0 + 1) and (R0 - 1)/(R0 + 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.

Keywords

  • genetics
  • epidemiology
  • disease resistance
  • livestock
  • R0

(To access the full article, please see PDF)

Authors’ Affiliations

(1)
Roslin Institute (Edinburgh), Roslin, Midlothian, EH25 9PS, UK
(2)
BioSS, Scottish Crop Research Institute, Invergowrie, Dundee, UK

Copyright

© INRA, EDP Sciences 2003

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