EpiCentre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand.
Prev Vet Med. 2012 Sep 1;106(1):63-74. doi: 10.1016/j.prevetmed.2012.02.021. Epub 2012 Apr 3.
This study aimed to develop a mathematical model describing the dynamics of paratuberculosis (PTB) in red deer (Cervus elaphus) under pastoral farming conditions in New Zealand. The model examined infectivity differences between ovine and bovine strains of Mycobacterium avium subspecies paratuberculosis (MAP) and seasonality of MAP survival. We also evaluate variable use of pasture and the effect of management interventions on the infection prevalence and annual clinical incidence of PTB. A state-transition model was developed and calibrated to observed data on both prevalence of infection and incidence of clinical PTB. To accommodate specific PTB features for deer, the model included a fast and a slow track for progression of infection to disease. MAP on pasture was the source for horizontal transmission and infected dams for vertical transmission. In the presence of a single strain, an infectivity reduction of up to 80% allowed MAP to persist in the herd (R(0)>1). For mixed infection by two strains however, a 30% reduction in infectivity of one strain was sufficient to outcompete a strain with lower infectivity, suggesting that mixed infection of MAP strains with different infectivity may not be common in deer. The model showed that seasonal variation of MAP survival on pasture had little impact on transmission dynamics, and that rotational grazing with pasture spelling vs. permanent grazing of the same paddock reduced both infection prevalence and clinical PTB by about 50%. Based on model outputs, early detection of young deer in a high-shedding state was the most effective means of controlling PTB among the tested scenarios.
本研究旨在建立一个数学模型，以描述新西兰放牧条件下红鹿（ Cervus elaphus ）中的副结核病（PTB）动态。该模型考察了禽分枝杆菌副结核亚种（MAP）的绵羊和牛菌株之间的传染性差异，以及 MAP 存活的季节性。我们还评估了牧场的可变使用情况，以及管理干预对感染流行率和 PTB 临床年度发病率的影响。开发并校准了一个状态转换模型，以适应对感染流行率和临床 PTB 发病率的观察数据。为了适应鹿的特定副结核病特征，该模型包括了感染向疾病进展的快速和慢速途径。牧场上的 MAP 是水平传播的来源，感染的母鹿是垂直传播的来源。在存在单一菌株的情况下，传染性降低高达 80%可以使 MAP 在畜群中持续存在（R(0)>1）。然而，对于两种菌株的混合感染，一种菌株的传染性降低 30%就足以竞争过传染性较低的菌株，这表明 MAP 菌株的混合感染与不同的传染性可能在鹿中并不常见。该模型表明，牧场上 MAP 存活的季节性变化对传播动态的影响很小，与永久性放牧相比，牧场轮牧和放牧休息可将感染流行率和临床 PTB 分别降低约 50%。根据模型输出，在高排放状态下早期检测幼鹿是控制检测场景中 PTB 的最有效手段。
