Genetic management strategies for controlling infectious diseases in livestock populations

• Main Authors: Bishop Stephen C, MacKenzie Katrin M
• Format: Article
• Language: deu
• Published: BMC 2003-06-01
• Series: Genetics Selection Evolution
• Subjects: genetics; epidemiology; disease resistance; livestock; R₀
• Online Access: http://www.gsejournal.org/content/35/S1/S3
• ISSN: 0999-193X; 1297-9686

<p>Abstract</p> <p>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 R₀below 1.0, <it>e.g</it>. 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 R₀₁describes transmission in the wildtype population. For an otherwise homogeneous population comprising animals of these two groups, R₀is the weighted average of the two sub-populations: R₀= R_{01<it>ρ </it>}+ R₀₂(1 - <it>ρ</it>), where <it>ρ </it>is the proportion of wildtype animals. If R₀₁> 1 and R₀₂< 1, the proportions of the two genotypes should be such that R₀≤ 1, <it>i.e</it>. <it>ρ </it>≤ (R₀- R₀₂)/(R₀₁- R₀₂). If R₀₂= 0, the proportion of resistant animals must be at least 1 - 1/R₀₁. For an <it>n </it>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.</p>