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Abstract：
Marek\'s disease virus (MDV), a poultry pathogen, has been increasing in virulence since the mid twentieth century. Since multiple vaccines have been developed and widely implemented, losses due to MDV have decreased. However, vaccine failure has occurred in the past and vaccine breakthroughs remain a problem. Failure of disease control with current vaccines would have significant economic and welfare consequences. Nevertheless, the epidemiology of the disease during a farm outbreak is not well understood. Here we present a mathematical model to predict the effectiveness of vaccines to reduce the outbreak probability and disease burden within a barn. We find that the chance of an outbreak within a barn increases with the virulence of an MDV strain, and is significantly reduced when the flock is vaccinated, especially when there the contaminant strain is of low virulence. With low quantities of contaminated dust, there is nearly a 100% effectiveness of vaccines to reduce MDV outbreaks. However, the vaccine effectiveness drops to zero with an increased amount of contamination with a middle virulence MDV strain. We predict that the larger the barn, and the more virulent the MDV strain is, the more virus is produced by the time the flock is slaughtered. With the low-to-moderate virulence of the strains studied here, the number of deaths due to MDV is very low compared to all-cause mortality regardless of the vaccination status of the birds. However, the cumulative MD incidence can reach 100% for unvaccinated cohorts, and 35% for vaccinated cohorts. These results suggest that death due to MDV is an insufficient metric to assess the prevalence of MDV broiler barns regardless of vaccine status, such that active surveillance is required to successfully assess the probability of MDV outbreaks, and to limit transmission of MDV between successive cohorts of broiler chickens.
摘要：
马立克氏病病毒（MDV），家禽病原体，自20世纪中叶以来，毒力一直在增加。由于已经开发并广泛实施了多种疫苗，MDV造成的损失有所减少。然而,过去发生过疫苗失败，疫苗突破仍然是一个问题。当前疫苗的疾病控制失败将产生重大的经济和福利后果。然而，在农场爆发期间，这种疾病的流行病学还没有得到很好的理解。在这里，我们提出了一个数学模型来预测疫苗的有效性，以减少谷仓内的爆发概率和疾病负担。我们发现，随着MDV毒株的毒力增加，谷仓内爆发的机会增加，当羊群接种疫苗时显著减少，特别是当污染菌株的毒力较低时。受污染的粉尘量低，疫苗在减少MDV爆发方面几乎100%有效.然而,随着中等毒力MDV毒株的污染量增加，疫苗的有效性下降到零。我们预测谷仓越大，MDV毒株的毒力越大，屠宰羊群时产生的病毒越多。由于这里研究的菌株的低至中等毒力，与全因死亡率相比,MDV导致的死亡人数非常低,无论禽类的疫苗接种状况如何.然而,未接种疫苗的人群的累积MD发病率可以达到100%，和35％的疫苗接种队列。这些结果表明，MDV导致的死亡不足以评估MDV肉鸡的流行程度，无论疫苗状况如何。因此，需要积极监测才能成功评估MDV爆发的可能性，并限制肉鸡连续队列之间MDV的传播。
