Miruk A, Hagos A, Yacob H T, Asnake F, Basu A K
Department of Pathology and Parasitology, Faculty of Veterinary Medicine, Addis Ababa University, P.O. Box 34, Debre Zeit, Ethiopia.
Vet Parasitol. 2008 Mar 25;152(1-2):141-7. doi: 10.1016/j.vetpar.2007.12.007. Epub 2007 Dec 14.
Cross-sectional studies were conducted in tsetse and non-tsetse-controlled areas of the Southern Nation Nationalities and Peoples Regional State (SNNPRS) of Ethiopia to determine the prevalence of bovine trypanosomosis as well as drug sensitivity tests on Trypanosoma congolense in both naturally and experimentally infected cattle and mice, respectively. A total trypanosome prevalence of 4.8% (95% CI: 1.8-7.5) and 20.4% (95% CI: 14-26.8) were recorded in the tsetse-controlled study area of Humbo district and the non-tsetse-controlled area of Mareka district, respectively, indicated statistically significant difference between the two areas (P<0.001). The mean PCV value for Humbo and Mareka was 26.2 (95%: 25.7-26.7) and 22.7 (95% CI: 22.1-23.3), respectively, which were also statistically significant (P<0.001). The prophylactic activity of isometamidium chloride (ISMM) was observed in Humbo on nine naturally positive zebu cattle. Breakthrough infections were recorded in (6/9) 66.7% of the cases in less than 5 weeks. A qualitative assay on mice was conducted on two T. congolense isolates obtained from the breakthrough cases with ranges of doses of ISMM and diminazene diaceturate (DA). Thereafter the mice were followed for relapse infection. ISMM at doses 0.5-4 mg/kg body weight (bw) and DA at doses of 3.5-28 mg/kg bw failed completely to cure T. congolense infections in any of the mice. A quantitative assay on mice was conducted on four T. congolense isolates obtained from Mareka. The four isolates were pooled into two pools (Pool-1 and Pool-2) for the quantitative assay on mice. The pooled isolates were tested with the same trypanocidal drugs and ranges of doses as it was used for the qualitative assay on mice. The minimum curative dose (MCD) of ISMM that cleared T. congolense infected mice was 4 and 2mg/kg bw for Pool-1 and Pool-2, respectively, whereas MCD of DA was 28 and 14 mg/kg bw, in Pool-1 and Pool-2, respectively. Although cloned populations were not used to prove whether the observed resistance was at the individual level or not, the results show that there is resistance to both ISMM and DA; failure of the "sanative pair".
在埃塞俄比亚南方民族和人民区域州（SNNPRS）的采采蝇控制区和非采采蝇控制区开展了横断面研究，以分别确定牛锥虫病的流行情况以及对自然感染和实验感染的牛与小鼠体内的刚果锥虫进行药敏试验。在洪博区的采采蝇控制研究区域和马雷卡区的非采采蝇控制区域，锥虫的总流行率分别记录为4.8%（95%置信区间：1.8 - 7.5）和20.4%（95%置信区间：14 - 26.8），这表明两个区域之间存在统计学上的显著差异（P<0.001）。洪博区和马雷卡区的平均红细胞压积值分别为26.2（95%：25.7 - 26.7）和22.7（95%置信区间：22.1 - 23.3），这同样具有统计学显著性（P<0.001）。在洪博区，对9头自然感染阳性的瘤牛观察了氯咪苯脲（ISMM）的预防活性。在不到5周的时间内，（6/9）66.7%的病例出现了突破性感染。对从突破性病例中获得的2株刚果锥虫分离株，用不同剂量的ISMM和双乙酰甲氧苄氨嘧啶（DA）对小鼠进行了定性试验。此后，对小鼠进行随访以观察复发感染情况。剂量为0.5 - 4mg/kg体重（bw）的ISMM和剂量为3.5 - 28mg/kg bw的DA均未能完全治愈任何一只小鼠的刚果锥虫感染。对从马雷卡区获得的4株刚果锥虫分离株对小鼠进行了定量试验。将这4株分离株合并为两个池（池1和池2）用于对小鼠的定量试验。对合并后的分离株使用与小鼠定性试验相同的杀锥虫药物和剂量范围进行测试。清除刚果锥虫感染小鼠的ISMM的最小治愈剂量（MCD），池1和池2分别为4mg/kg bw和2mg/kg bw，而DA在池1和池2中的MCD分别为28mg/kg bw和14mg/kg bw。尽管未使用克隆群体来证明观察到的耐药性是否处于个体水平，但结果表明对ISMM和DA均存在耐药性；即“治疗组合”失效。
