Johne's disease is a progressive, chronic disease with inflammation of the small intestine of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). Accurately estimating prevalence of MAP infections is important when controlling spread of infection or monitoring effectiveness of control programs. In the absence of a consistent test method used in prevalence studies across Canada, prevalence estimates among regions and programs cannot be compared. The aim of the current study was to estimate and compare prevalence of MAP infection in Western Canada, Ontario, Québec, and the Atlantic provinces, as well as among varying herd sizes and housing types. On 362 dairy farms located in all 10 provinces of Canada, environmental samples were collected and cultured for detection of MAP. For each herd, 1 sample was collected from the lactating cow area and manure storage. An additional environmental sample was collected from the area where breeding-age heifers were housed. Using prior distributions from previous research, diagnostic sensitivity and specificity were calculated to assess the ability of only 2 environmental samples (manure storage and lactating cow area) to identify MAP-positive farms, resulting in a sensitivity and specificity of 38 and 100%, respectively. We found no difference in sensitivity and specificity when including breeding-age heifers environmental samples. Test characteristics were applied to environmental culture results from the 362 participating farms in all 4 regions, resulting in true prevalence estimates of 66% for farms in Western Canada, 54% in Ontario, 24% in Québec, and 47% in Atlantic Canada. Herds housed in tiestalls had lower prevalence than freestall-housed herds, and herds with 101–150 and >151 cows had higher prevalence than herds with ≤100 cows. This was the first time MAP prevalence was determined using 1 detection method, performed in 1 laboratory, and within a single year across Canada, enabling direct comparisons of prevalence among regions, housing types, and herd sizes.

约翰尼氏病是由鸟分枝杆菌亚种副结核病引起的反刍动物小肠发炎的进行性慢性疾病（地图）。当控制感染的传播或监测控制程序的有效性时，准确估计MAP感染的发生率很重要。在加拿大流行率研究中缺乏一致的测试方法的情况下，无法比较各地区和计划之间的流行率估计值。本研究的目的是评估和比较加拿大西部，安大略省，魁北克省和大西洋省以及不同畜群规模和住房类型之间的MAP感染率。在加拿大所有10个省的362个奶牛场中，收集了环境样品并进行了培养以检测MAP。对于每只牛群，从泌乳母牛区域和粪便存储中收集了1个样品。从饲养有繁殖期小母牛的区域收集了另外的环境样品。使用先前研究的先前分布，计算出诊断敏感性和特异性，以评估仅2个环境样品（粪便存储和泌乳母牛区域）识别MAP阳性农场的能力，导致敏感性和特异性分别为38％和100％ 。当包括育龄母牛的环境样本时，我们发现敏感性和特异性没有差异。测试特征应用于来自所有4个地区的362个农场的环境养殖结果，得出的真实流行率估计为：加拿大西部的农场为66％，安大略省为54％，魁北克为24％，加拿大大西洋为47％。饲养在牛棚中的牛群的流行率要低于寄养牛的牛群，牛群101–150和> 151的牛群的患病率要高于牛群≤100的牛群。