Dwyer G, Elkinton J S, Buonaccorsi J P
Department of Entomology, Fernald Hall, University of Massachusetts, Amherst, Massachusetts 01003-2410, USA.
Am Nat. 1997 Dec;150(6):685-707. doi: 10.1086/286089.
Most mathematical models of disease assume that transmission is linearly dependent on the densities of host and pathogen. Recent data for animal diseases, however, have cast doubt on this assumption, without assessing the usefulness of alternative models. In this article, we use a combination of laboratory dose-response experiments, field transmission experiments, and observations of naturally occurring populations to show that virus transmission in gypsy moths is a nonlinear function of virus density, apparently because of heterogeneity among individual gypsy moth larvae in their susceptibility to the virus. Dose-response experiments showed that larvae from a laboratory colony of gypsy moths are substantially less heterogeneous in their susceptibility to the virus than are larvae from feral populations, and field experiments showed that there is a more strongly nonlinear relationship between transmission and virus density for feral larvae than for lab larvae. This nonlinearity in transmission changes the dynamics of the virus in natural populations so that a model incorporating host heterogeneity in susceptibility to the virus gives a much better fit to data on virus dynamics from large-scale field plots than does a classical model that ignores host heterogeneity. Our results suggest that heterogeneity among individuals has important effects on the dynamics of disease in insects at several spatial and temporal scales and that heterogeneity in susceptibility may be of general importance in the ecology of disease.
大多数疾病的数学模型都假定传播与宿主和病原体的密度呈线性相关。然而，近期有关动物疾病的数据对这一假设提出了质疑，却未评估其他模型的实用性。在本文中，我们结合实验室剂量反应实验、野外传播实验以及对自然种群的观察，以表明舞毒蛾中的病毒传播是病毒密度的非线性函数，这显然是由于舞毒蛾幼虫个体对病毒的易感性存在异质性。剂量反应实验表明，来自实验室舞毒蛾种群的幼虫对病毒的易感性差异远小于野生种群的幼虫，野外实验表明，野生幼虫的传播与病毒密度之间的非线性关系比实验室幼虫更为强烈。这种传播的非线性改变了自然种群中病毒的动态，因此，一个纳入宿主对病毒易感性异质性的模型，比一个忽略宿主异质性的经典模型，能更好地拟合大规模野外样地中病毒动态的数据。我们的结果表明，个体间的异质性在几个空间和时间尺度上对昆虫疾病动态具有重要影响，并且易感性的异质性在疾病生态学中可能具有普遍重要性。
