Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, 060-0818, Japan.
Parasitol Res. 2013 Apr;112(4):1513-21. doi: 10.1007/s00436-013-3297-3. Epub 2013 Jan 25.
In recent years, the emergence of highly pathogenic Trypanosoma evansi strains in the Philippines has resulted in substantial losses in livestock production. In this study, we isolated T. evansi from infected-water buffaloes in the Philippines and analyzed their virulence using mice and cattle. A total of 10 strains of T. evansi were isolated. Evaluation of the virulence of each strain using mice depicted significant differences among the strains in the prepatent period, the level of parasitemia, and the survival time of the infected animals. In mice infected with the highly pathogenic T. evansi, signs of excessive inflammation such as marked splenomegaly and increase more than 6-fold in the number of leukocytes were observed at 8 days post-infection. To study the virulence of the parasite strains in cattle (which are the common T. evansi hosts in Philippines), cattle were infected with the T. evansi isolates that showed high and low virulence in mice. The rate of parasite growth and the length of the prepatent periods were found to be similar to those observed in mice for the respective strains. The cattle infected with the highly pathogenic strain developed anemia and a marked decrease in leukocyte counts. To determine the cause of the pathological changes, we analyzed the expression levels of inflammatory cytokines and observed up-regulation of tumor necrosis factor-α in anemic infected cattle. Our findings suggest that the epidemic of T. evansi in the Philippines is characterized by T. evansi strains with varying virulences from low to very high pathogenicity in cattle.
近年来，菲律宾出现了高致病性伊氏锥虫菌株，导致畜牧业生产遭受重大损失。在本研究中，我们从菲律宾感染的水牛中分离出伊氏锥虫，并使用小鼠和牛分析其毒力。共分离出 10 株伊氏锥虫。用小鼠评估各菌株的毒力，结果显示在潜隐期、寄生虫血症水平和感染动物的存活时间方面，各菌株之间存在显著差异。在感染高致病性伊氏锥虫的小鼠中，感染后 8 天观察到过度炎症的迹象，如明显的脾肿大和白细胞数量增加 6 倍以上。为了研究寄生虫株在牛（菲律宾常见的伊氏锥虫宿主）中的毒力，用在小鼠中显示高和低毒力的伊氏锥虫分离株感染牛。发现寄生虫的生长速度和潜隐期与相应菌株在小鼠中观察到的相似。感染高致病性菌株的牛出现贫血和白细胞计数明显下降。为了确定病理变化的原因，我们分析了炎症细胞因子的表达水平，观察到贫血感染牛中肿瘤坏死因子-α的上调。我们的研究结果表明，菲律宾伊氏锥虫的流行特征是牛中的伊氏锥虫菌株具有从低到非常高的致病性的不同毒力。
