Department of Integrative Biology, University of California, Berkeley, Valley Life Sciences Building, Berkeley, CA 94720, USA; Department of Mathematics and Statistics, Queen's University, Jeffery Hall, Kingston, ON, K7L 3N6, Canada.
Department of Mathematics and Statistics, Queen's University, Jeffery Hall, Kingston, ON, K7L 3N6, Canada.
Epidemics. 2019 Jun;27:52-58. doi: 10.1016/j.epidem.2019.01.004. Epub 2019 Feb 2.
The industrialization of farming has had an enormous impact. To most, this impact is viewed solely in the context of productivity, but the denser living conditions and shorter rearing periods of industrial livestock farms provide pathogens with an ideal opportunity to spread and evolve. For example, the industrialization of poultry farms drove the Marek's disease virus (MDV) to evolve from a mild paralytic syndrome to a highly contagious, globally prevalent, deadly disease. Fortunately, the economic catastrophe that would occur from MDV evolution is prevented through the widespread use of live imperfect vaccines that limit disease symptoms, but fail to prevent transmission. Unfortunately, the continued rollout of such imperfect vaccines is steering MDV evolution towards even greater virulence, and the ability to evade vaccine protection. Thus, there is a need to investigate alternative economically viable control measures for their ability to inhibit MDV spread and evolution. In what follows we examine the economic viability of standard husbandry practices for their ability to inhibit the spread of both virulent MDV and very virulent MDV throughout an industrialized egg farm. To do this, we parameterize a MDV transmission model and calculate the loss in egg production due to MDV. We find that MDV strain and the cohort duration have the greatest influence on both disease burden and egg production. Additionally, our findings show that for long cohort durations, conventional cages result in the least per capita loss in egg production due to MDV infection, while Aviary systems perform best over shorter cohort durations. Finally, we find that the least per capita loss in egg production for flocks infected with the more virulent MDV strains occurs when cohort durations are sufficiently short. These results highlight the important decisions that managers will face when implementing new hen husbandry practices.
农业工业化产生了巨大的影响。在大多数情况下，这种影响仅从生产力的角度来看待，但工业化养殖场中密集的生活条件和更短的饲养周期为病原体的传播和进化提供了理想的机会。例如，家禽养殖场的工业化使马立克氏病病毒（MDV）从轻度瘫痪综合征演变为高度传染性、普遍存在且致命的疾病。幸运的是，通过广泛使用限制疾病症状但无法阻止传播的活不完美疫苗，防止了 MDV 进化带来的经济灾难。不幸的是，这些不完美疫苗的持续推广正在促使 MDV 朝着更高的毒力和逃避疫苗保护的方向进化。因此，需要研究替代的经济可行的控制措施，以评估它们抑制 MDV 传播和进化的能力。在接下来的内容中，我们研究了标准饲养实践在抑制致命 MDV 和非常致命 MDV 在整个工业化蛋鸡场传播和进化方面的经济可行性。为此，我们对 MDV 传播模型进行了参数化，并计算了 MDV 导致的鸡蛋产量损失。我们发现，MDV 株系和群体持续时间对疾病负担和鸡蛋产量都有最大的影响。此外，我们的研究结果表明，对于较长的群体持续时间，由于 MDV 感染，传统鸡笼导致的人均鸡蛋产量损失最小，而禽类系统在较短的群体持续时间内表现最佳。最后，我们发现，当群体持续时间足够短时，感染更致命 MDV 株系的鸡群的人均鸡蛋产量损失最小。这些结果突出了管理者在实施新的母鸡饲养实践时将面临的重要决策。
