Department of Medical Parasitology, Postgraduate Institute of Medical Education & Research, Chandigarh, 160012, India.
Advanced Eye Centre, Postgraduate Institute of Medical Education & Research, Chandigarh, 160012, India.
Parasitol Res. 2023 Sep;122(9):2109-2118. doi: 10.1007/s00436-023-07910-7. Epub 2023 Jul 7.
Acanthamoeba are free-living protozoa present ubiquitously in numerous environmental reservoirs that exist as an actively feeding trophozoite or a dormant cyst stage. The pathogenic Acanthamoeba are known to cause Acanthamoeba keratitis (AK) and granulomatous amoebic encephalitis (GAE). Despite their omnipresence, the number of infections is quite low. The reason behind this low frequency of Acanthamoeba infections could be the existence of many non-pathogenic strains or a successful host immune response to these infections. Studies in the past have proposed a few physiological parameters for the differentiation of pathogenic and non-pathogenic strains. Additionally, in vivo experiments are known to play an essential role in understanding the virulence of parasites, immunological aspects, and disease pathogenesis. The thermotolerance (30 °C, 37 °C, and 40 °C) and osmotolerance (0.5 M, 1 M, and 1.5 M) tests were performed on 43 Acanthamoeba isolates from patients with keratitis (n = 22), encephalitis (n = 5), and water samples (n = 16). In addition, the genotype of 10 Acanthamoeba isolates (keratitis (n = 2), encephalitis (n = 2), water (n = 6)) was determined and were then evaluated for pathogenicity on mouse model by inducing Acanthamoeba keratitis and amoebic encephalitis. The results of the thermotolerance and osmotolerance assays categorized 29/43 (67.4%) isolates as pathogenic, 8 as low pathogenic (18.6%), and the remaining 6 (13.9%) as non-pathogenic. The 10 Acanthamoeba isolates were categorized as T11 (5 isolates), T5 (2 isolates), T4 (2 isolates), and T10 (1 isolate) genotypes. Out of 10 Acanthamoeba isolates, 9 were successful in establishing AK, amoebic encephalitis, or both in the mice model, and a single isolate was found non-pathogenic. Two isolates from water samples were non-pathogenic in the physiological tests but successfully established Acanthamoeba infection in the mice model. The results of the physiological assays and in vivo experiments were analogous for 7 isolates while 1 isolate from the water was low pathogenic in the physiological assays but failed to produce pathogenicity during in vivo experiments. The physiological parameters are not very dependable to test the pathogenic potential of Acanthamoeba isolates, and thus results must always be validated by in vivo experiments. There is no infallible approach for determining the potential pathogenicity of environmental isolates of Acanthamoeba because several parameters regulate the pathogenic potential.
棘阿米巴是自由生活的原生动物，广泛存在于多种环境储层中，以活跃的滋养体或休眠的孢囊形式存在。已知致病性棘阿米巴可引起棘阿米巴角膜炎（AK）和肉芽肿性阿米巴脑炎（GAE）。尽管它们无处不在，但感染的数量却相当低。这种棘阿米巴感染频率较低的原因可能是存在许多非致病性株或宿主对这些感染有成功的免疫反应。过去的研究提出了一些用于区分致病性和非致病性株的生理参数。此外，体内实验在了解寄生虫的毒力、免疫学方面和疾病发病机制方面起着至关重要的作用。对来自角膜炎患者（n=22）、脑炎患者（n=5）和水样（n=16）的 43 株棘阿米巴分离物进行了耐热性（30°C、37°C 和 40°C）和耐渗透压性（0.5M、1M 和 1.5M）测试。此外，还确定了 10 株棘阿米巴分离物（角膜炎（n=2）、脑炎（n=2）、水（n=6））的基因型，然后通过诱导棘阿米巴角膜炎和阿米巴性脑炎在小鼠模型中评估其致病性。耐热性和耐渗透压性测定的结果将 29/43（67.4%）株归类为致病性，8 株为低致病性（18.6%），其余 6 株（13.9%）为非致病性。10 株棘阿米巴分离物被归类为 T11（5 株）、T5（2 株）、T4（2 株）和 T10（1 株）基因型。在 10 株棘阿米巴分离物中，有 9 株在小鼠模型中成功建立 AK、阿米巴性脑炎或两者均成功建立，有 1 株分离物被认为是非致病性的。水样中的 2 株分离物在生理试验中是非致病性的，但在小鼠模型中成功建立了棘阿米巴感染。生理试验和体内实验的结果对 7 株分离物相似，而水样中的 1 株分离物在生理试验中为低致病性，但在体内实验中未能产生致病性。生理参数并不能非常可靠地测试棘阿米巴分离物的致病潜力，因此结果必须始终通过体内实验验证。由于有几个参数调节致病潜力，因此没有一种确定环境分离的棘阿米巴潜在致病性的万无一失的方法。
