BACKGROUND Microparasitic diseases are caused by bacteria and viruses. Genetic improvement of resistance to microparasitic diseases in breeding programs is desirable and should aim at reducing the basic reproduction ratio [Formula: see text]. Recently, we developed a method to derive the economic value of [Formula: see text] for macroparasitic diseases. In epidemiological models for microparasitic diseases, an animal's disease status is treated as infected or not infected, resulting in a definition of [Formula: see text] that differs from that for macroparasitic diseases. Here, we extend the method for the derivation of the economic value of [Formula: see text] to microparasitic diseases. METHODS When [Formula: see text], the economic value of [Formula: see text] is zero because the disease is very rare. When [Formula: see text]. is higher than 1, genetic improvement of [Formula: see text] can reduce expenditures on vaccination if vaccination induces herd immunity, or it can reduce production losses due to disease. When vaccination is used to achieve herd immunity, expenditures are proportional to the critical vaccination coverage, which decreases with [Formula: see text]. The effect of [Formula: see text] on losses is considered separately for epidemic and endemic disease. Losses for epidemic diseases are proportional to the probability and size of major epidemics. Losses for endemic diseases are proportional to the infected fraction of the population at the endemic equilibrium. RESULTS When genetic improvement reduces expenditures on vaccination, expenditures decrease with [Formula: see text] at an increasing rate. When genetic improvement reduces losses in epidemic or endemic diseases, losses decrease with [Formula: see text] at an increasing rate. Hence, in all cases, the economic value of [Formula: see text] increases as [Formula: see text] decreases towards 1. DISCUSSION [Formula: see text] and its economic value are more informative for potential benefits of genetic improvement than heritability estimates for survival after a disease challenge. In livestock, the potential for genetic improvement is small for epidemic microparasitic diseases, where disease control measures limit possibilities for phenotyping. This is not an issue in aquaculture, where controlled challenge tests are performed in dedicated facilities. If genetic evaluations include infectivity, genetic gain in [Formula: see text] can be accelerated but this would require different testing designs. CONCLUSIONS When [Formula: see text], its economic value is zero. The economic value of [Formula: see text] is highest at low values of [Formula: see text] and approaches zero at high values of [Formula: see text].

中文翻译：

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R0对微寄生虫病的选择性育种的经济价值。

背景技术微寄生虫病是由细菌和病毒引起的。在育种计划中对微寄生虫病的抗性进行遗传改良是可取的，并且应以降低基本繁殖率为目标[公式：见正文]。最近，我们开发了一种方法来推导[寄生虫]的经济价值。在微寄生虫疾病的流行病学模型中，将动物的疾病状况视为已感染或未感染，导致[公式：参见文字]的定义与大寄生虫疾病的定义不同。在这里，我们将推导[公式：参见文本]的经济价值的方法扩展到微寄生虫疾病。方法当[公式：参见文本]时，[公式：参见文本]的经济价值为零，因为这种疾病非常罕见。当[公式：参见文字]。高于1时，如果疫苗接种可诱导畜群免疫，则遗传改良可以减少疫苗接种的支出，或者可以减少疾病引起的生产损失。当使用疫苗接种以实现畜群免疫时，支出与关键疫苗接种覆盖率成正比，该覆盖率随[公式：参见文本]而减少。对于流行病和地方病，[公式：参见文字]对损失的影响被单独考虑。流行病的损失与主要流行病的可能性和大小成正比。地方病的损失与地方病平衡时人口的感染比例成正比。结果当遗传改良减少了疫苗接种费用时，[公式：见正文]的支出将以增加的速度减少。当遗传改良减少流行病或地方病的损失时，[公式：见正文]的损失将以增加的速度减少。因此，在所有情况下，[公式：参见文本]的经济价值都随着[公式：参见文本]朝1的降低而增加。讨论[公式：参见文本]及其经济价值对于遗传改良的潜在益处比可遗传性更具参考价值。评估疾病挑战后的生存率。在牲畜中，流行的微寄生虫疾病的遗传改良潜力很小，因为疾病控制措施限制了表型的可能性。在水产养殖中，这不是一个问题，因为在专用设施中进行了受控挑战测试。如果遗传评估包括传染性，则[公式：可以加快速度，但这需要不同的测试设计。结论当[公式：见正文]时，其经济价值为零。[公式：参见文本]的经济价值在[公式：参见文本]的低值处最高，而在[公式：参见文本]的高值处接近零。