对新西兰奶牛场中循环传播的微小隐孢子虫的流行率、遗传多样性和人畜共患病潜力的横断面研究。
Cross sectional study of prevalence, genetic diversity and zoonotic potential of Cryptosporidium parvum cycling in New Zealand dairy farms.
作者信息
Al Mawly Julanda, Grinberg Alex, Velathanthiri Niluka, French Nigel
机构信息
mEpiLab, Hopkirk Research Institute, Massey University, Palmerston North, New Zealand.
Infectious Diseases Group, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11-222, Palmerston North, New Zealand.
出版信息
Parasit Vectors. 2015 Apr 22;8:240. doi: 10.1186/s13071-015-0855-9.
BACKGROUND
The estimation of the prevalence and zoonotic potential of Cryptosporidium parvum cycling in bovine populations requires the use of genotyping, as several morphologically similar non-parvum genetic variants of unproven clinical and public health impact are found in cattle. However, robust C. parvum prevalence estimates in cattle are lacking and comparative data of bovine and human isolates collected from the same regions are scarce. Thus, the relative contribution of the C. parvum oocysts released by farmed animals to animal and human cryptosporidiosis burden is, in general, poorly understood.
METHODS
The New Zealand farm-level C. parvum prevalence was estimated using a cross-sectional sample of 1283 faecal specimens collected from newborn calves on 97 dairy farms. Faeces were analysed by immunofluorescence and the Cryptosporidium parasites were genetically identified. Finally, bovine C. parvum were genetically compared with historical human clinical isolates using a bilocus subtyping scheme.
RESULTS
Immunofluoresence-positive faeces were found in 63/97 (65%) farms. C. parvum was identified in 49 (50.5%) farms, C. bovis in 6 (6.1%) farms, and on 8 (8.2%) farms the species could not be identified. The dominant C. parvum genetic variants were geographically widespread and found in both host populations, but several variants were found in humans only.
CONCLUSIONS
Phenotypic tests offered by New Zealand veterinary diagnostic laboratories for the diagnosis of C. parvum may have moderate to high positive predictive values for this species. The genetic similarities observed between the human and bovine parasites support a model considering calves as significant amplifiers of zoonotic C. parvum in New Zealand. However, data suggest that transmission routes not associated with dairy cattle should also be taken into account in future source-attribution studies of human cryptosporidiosis.
背景
由于在牛群中发现了几种形态相似但未经证实对临床和公共卫生有影响的非微小隐孢子虫遗传变体，因此估计微小隐孢子虫在牛群中的流行率及其人畜共患病潜力需要进行基因分型。然而，目前缺乏对牛群中微小隐孢子虫流行率的可靠估计，且从同一地区收集的牛和人分离株的比较数据也很稀少。因此，一般来说，人们对养殖动物释放的微小隐孢子虫卵囊对动物和人类隐孢子虫病负担的相对贡献了解甚少。
方法
利用从97个奶牛场的新生犊牛采集的1283份粪便标本的横断面样本，估计新西兰农场层面微小隐孢子虫的流行率。通过免疫荧光分析粪便，并对隐孢子虫寄生虫进行基因鉴定。最后，使用双位点亚型分型方案对牛微小隐孢子虫与历史人类临床分离株进行基因比较。
结果
在63/97（65%）的农场中发现了免疫荧光阳性粪便。在49个（50.5%）农场中鉴定出微小隐孢子虫，在6个（6.1%）农场中鉴定出牛隐孢子虫，在8个（8.2%）农场中无法鉴定出该物种。主要的微小隐孢子虫遗传变体在地理上广泛分布，且在两个宿主群体中均有发现，但有几种变体仅在人类中发现。
结论
新西兰兽医诊断实验室提供的用于诊断微小隐孢子虫的表型检测对该物种可能具有中度至高阳性预测值。在人和牛寄生虫之间观察到的基因相似性支持了一种模型，即认为犊牛是新西兰人畜共患微小隐孢子虫的重要扩增宿主。然而，数据表明，在未来人类隐孢子虫病的来源归因研究中，也应考虑与奶牛无关的传播途径。
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