Genet. Sel. Evol.
Volume 35, Number Suppl. 1, 2003Second International Symposium on Candidate Genes for Animal Health
|Page(s)||S3 - S17|
Genetic management strategies for controlling infectious diseases in livestock populationsStephen C. Bishopa and Katrin M. MacKenziea, b
a Roslin Institute (Edinburgh), Roslin, Midlothian, EH25 9PS, UK
b Current address: BioSS, Scottish Crop Research Institute, Invergowrie, Dundee, UK
(Accepted 4 February 2003)
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 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 , 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 01 ( ), where is the proportion of wildtype animals. If R 01 > 1 and R 02 < 1, the proportions of the two genotypes should be such that , i.e. . If R 02 = 0, the proportion of resistant animals must be at least . For an n genotype model the requirement is still to have . 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 . When the probability of a minor epidemic, which dies out without intervention, is . When the probability of a minor and major epidemics are and . 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.
Key words: genetics / epidemiology / disease resistance / livestock / R 0
Correspondence and reprints: S.C. Bishop
© INRA, EDP Sciences 2003