Genetic management strategies for controlling infectious diseases in livestock populations

<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 R<sub>0</sub>, the basic reproductive ratio of a pathogen. If R<sub>0 </sub>>...

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Bibliographic Details
Main Authors: Bishop Stephen C, MacKenzie Katrin M
Format: Article
Language:deu
Published: BMC 2003-06-01
Series:Genetics Selection Evolution
Subjects:
Online Access:http://www.gsejournal.org/content/35/S1/S3
Description
Summary:<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 R<sub>0</sub>, the basic reproductive ratio of a pathogen. If R<sub>0 </sub>> 1.0 a major epidemic can occur, thus a disease control strategy should aim to reduce R<sub>0 </sub>below 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 R<sub>02 </sub>< R<sub>01</sub>, where R<sub>01 </sub>describes transmission in the wildtype population. For an otherwise homogeneous population comprising animals of these two groups, R<sub>0 </sub>is the weighted average of the two sub-populations: R<sub>0 </sub>= R<sub>01<it>ρ </it></sub>+ R<sub>02 </sub>(1 - <it>ρ</it>), where <it>ρ </it>is the proportion of wildtype animals. If R<sub>01 </sub>> 1 and R<sub>02 </sub>< 1, the proportions of the two genotypes should be such that R<sub>0 </sub>≤ 1, <it>i.e</it>. <it>ρ </it>≤ (R<sub>0 </sub>- R<sub>02</sub>)/(R<sub>01 </sub>- R<sub>02</sub>). If R<sub>02 </sub>= 0, the proportion of resistant animals must be at least 1 - 1/R<sub>01</sub>. For an <it>n </it>genotype model the requirement is still to have R<sub>0 </sub>≤ 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<sub>0 </sub>+ 1). When R<sub>0 </sub>≤ 1 the probability of a minor epidemic, which dies out without intervention, is R<sub>0</sub>/(R<sub>0 </sub>+ 1). When R<sub>0 </sub>> 1 the probability of a minor and major epidemics are 1/(R<sub>0 </sub>+ 1) and (R<sub>0 </sub>- 1)/(R<sub>0 </sub>+ 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>
ISSN:0999-193X
1297-9686