Allen P C, Danforth H D, Augustine P C
USDA/ARS, Livestock and Poultry Sciences Institute, Parasite Biology and Epidemiology Laboratory, Beltsville, MD 20705, USA.
Int J Parasitol. 1998 Jul;28(7):1131-40. doi: 10.1016/s0020-7519(98)00029-0.
During the past several years, our laboratory has been investigating the anticoccidial activities of various natural products that have potential use as dietary supplements for coccidiosis control. Sources of fats containing high concentrations of n-3 fatty acids such as menhaden oil and flaxseed oil and flaxseed, when added to starter rations and fed to chicks from one day of age, effectively reduce lesions caused by the caecal parasite Eimeria tenella, but not lesions caused by Eimeria maxima. Our results are consistent with reports of effects of diets high in n-3 fatty acids on other protozoan parasites which suggest that the state of oxidative stress induced by these diets in the cells of both host and parasites is responsible for their parasitic actions. Artemisinin, a naturally occurring (Artemisia annua) endoperoxide and effective antimalarial significantly lowers lesions from E. tenella when given at low levels as a feed additive. The mechanism of its action is also considered to involve induction of oxidative stress. Diets supplemented with 8 p.p.m. gamma-tocopherol (abundant in flaxseeds) or with 1% of the spice tumeric, reduce mid-small intestinal lesion scores and improve weight gains during E. maxima infections. These compounds may exert their anticoccidial activity because they are effective antioxidants. Betaine, a choline analogue found in high concentrations in sugar beets, improves nutrient utilisation by animals under stress. When provided as a dietary supplement at a level of 0.15% it has enhanced the anticoccidial activity of the ionophore, salinomycin. Betaine may act as an osmoprotectant whereby it improves the integrity and function of the infected intestinal mucosa. In in vivo studies, betaine plus salinomycin significantly inhibit invasion of both E. tenella and E. acervulina. However, subsequent development of E. acervulina is inhibited more effectively with this combination treatment than development of E. tenella.
在过去几年中，我们实验室一直在研究各种天然产物的抗球虫活性，这些天然产物有潜力用作控制球虫病的膳食补充剂。含有高浓度n-3脂肪酸的脂肪来源，如鲱鱼油、亚麻籽油和亚麻籽，从雏鸡一日龄起添加到起始日粮中并喂食，可有效减少盲肠寄生虫柔嫩艾美耳球虫引起的病变，但不能减少巨型艾美耳球虫引起的病变。我们的结果与关于高n-3脂肪酸饮食对其他原生动物寄生虫影响的报道一致，这些报道表明这些饮食在宿主和寄生虫细胞中诱导的氧化应激状态是其寄生作用的原因。青蒿素是一种天然存在的（黄花蒿）内过氧化物，是有效的抗疟药物，作为饲料添加剂低剂量给药时，能显著降低柔嫩艾美耳球虫引起的病变。其作用机制也被认为与氧化应激的诱导有关。添加8 ppmγ-生育酚（亚麻籽中含量丰富）或1%香料姜黄的日粮，可降低巨型艾美耳球虫感染期间中小肠病变评分并提高体重增加。这些化合物可能因其是有效的抗氧化剂而发挥抗球虫活性。甜菜碱是一种在甜菜中高浓度存在的胆碱类似物，可提高应激状态下动物的营养利用率。以0.15%的水平作为膳食补充剂提供时，它增强了离子载体盐霉素的抗球虫活性。甜菜碱可能作为一种渗透保护剂，从而改善受感染肠黏膜的完整性和功能。在体内研究中，甜菜碱加氯苯胍显著抑制柔嫩艾美耳球虫和堆型艾美耳球虫的侵入。然而，这种联合治疗对堆型艾美耳球虫后续发育的抑制比对柔嫩艾美耳球虫发育的抑制更有效。
