Ivermectin treatment of Loa loa hyper-microfilaraemic baboons (Papio anubis): Assessment of microfilarial load reduction, haematological and biochemical parameters and histopathological changes following treatment

BackgroundIndividuals with high intensity of Loa loa are at risk of developing serious adverse events (SAEs) post treatment with ivermectin. These SAEs have remained unclear and a programmatic impediment to the advancement of community directed treatment with ivermectin. The pathogenesis of these SAEs following ivermectin has never been investigated experimentally. The Loa/baboon (Papio anubis) model can be used to investigate the pathogenesis of Loa-associated encephalopathy following ivermectin treatment in humans.Methods12 baboons with microfilarial loads > 8,000mf/mL of blood were randomised into four groups: Group 1 (control group receiving no drug), Group 2 receiving ivermectin (IVM) alone, Group 3 receiving ivermectin plus aspirin (IVM + ASA), and Group 4 receiving ivermectin plus prednisone (IVM + PSE). Blood samples collected before treatment and at Day 5, 7 or 10 post treatment, were analysed for parasitological, hematological and biochemical parameters using standard techniques. Clinical monitoring of animals for side effects took place every 6 hours post treatment until autopsy. At autopsy free fluids and a large number of standard organs were collected, examined and tissues fixed in 10% buffered formalin and processed for standard haematoxylin-eosin staining and specific immunocytochemical staining.ResultsMf counts dropped significantly (p0.05). All animals became withdrawn 48 hours after IVM administration. All treated animals recorded clinical manifestations including rashes, itching, diarrhoea, conjunctival haemorrhages, lymph node enlargement, pinkish ears, swollen face and restlessness; one animal died 5 hours after IVM administration. Macroscopic changes in post-mortem tissues observed comprised haemorrhages in the brain, lungs, heart, which seen in all groups given ivermectin but not in the untreated animals. Microscopically, the major cellular changes seen, which were present in all the ivermectin treated animals included microfilariae in varying degrees of degeneration in small vessels. These were frequently associated with fibrin deposition, endothelial changes including damage to the integrity of the blood vessel and the presence of extravascular erythrocytes (haemorrhages). There was an increased presence of eosinophils and other chronic inflammatory types in certain tissues and organs, often in large numbers and associated with microfilarial destruction. Highly vascularized organs like the brain, heart, lungs and kidneys were observed to have more microfilariae in tissue sections. The number of mf seen in the brain and kidneys of animals administered IVM alone tripled that of control animals. Co-administration of IVM + PSE caused a greater increase in mf in the brain and kidneys while the reverse was noticed with the co-administration of IVM + ASA.ConclusionsThe treatment of Loa hyper-microfilaraemic individuals with ivermectin produces a clinical spectrum that parallels that seen in Loa hyper-microfilaraemic humans treated with ivermectin. The utilization of this experimental model can contribute to the improved management of the adverse responses in humans.

研究背景：罗阿丝虫（Loa loa）感染负荷较高的个体，在接受伊维菌素（ivermectin, IVM）治疗后有发生严重不良事件（serious adverse events, SAEs）的风险。此类严重不良事件的发病机制尚未阐明，且成为伊维菌素社区主导治疗推进的程序性障碍。伊维菌素治疗后此类严重不良事件的发病机制尚未经实验研究探究。罗阿丝虫-橄榄狒狒（Papio anubis）动物模型可用于探究人类接受伊维菌素治疗后罗阿丝虫相关性脑病的发病机制。

研究方法：12只血液微丝蚴负荷＞8000条/mL的橄榄狒狒被随机分为4组：第1组为对照组（不予给药），第2组仅接受伊维菌素治疗，第3组接受伊维菌素联合阿司匹林（aspirin, ASA）治疗，第4组接受伊维菌素联合泼尼松（prednisone, PSE）治疗。于治疗前及治疗后第5、7或10天采集血液样本，采用标准技术对样本的寄生虫学、血液学及生化指标进行检测分析。于治疗后每6小时对动物进行不良反应临床监测，直至剖检。剖检时采集游离体液及大量常规器官组织，将组织固定于10%缓冲福尔马林溶液中，随后进行标准苏木精-伊红（HE）染色及特异性免疫细胞化学染色处理。

研究结果：微丝蚴计数显著下降（p0.05）。所有接受伊维菌素治疗的动物在给药后48小时均出现精神萎靡状态。所有给药动物均出现临床症状，包括皮疹、瘙痒、腹泻、结膜出血、淋巴结肿大、耳色发红、面部肿胀及躁动不安；其中1只动物在伊维菌素给药后5小时死亡。剖检组织可见大体病理学改变：脑、肺、心脏存在出血现象，该改变见于所有接受伊维菌素治疗的组，而未给药对照组未出现此类改变。镜下可见所有伊维菌素治疗组动物均出现主要细胞病变：小血管内存在不同程度变性的微丝蚴；此类病变常伴随纤维蛋白沉积、血管内皮损伤（包括血管完整性破坏）以及血管外红细胞渗出（即出血）。部分组织器官中嗜酸性粒细胞及其他慢性炎性细胞浸润增加，且常呈大量浸润，与微丝蚴破坏相关。高血管化器官如脑、心脏、肺及肾脏的组织切片中可见更多微丝蚴。仅接受伊维菌素治疗的动物，其脑与肾脏组织中可见的微丝蚴数量为对照组的3倍。伊维菌素联合泼尼松给药组的脑与肾脏组织中微丝蚴数量进一步升高，而伊维菌素联合阿司匹林给药组则呈现相反的变化趋势。

研究结论：高微丝蚴负荷的罗阿丝虫感染个体接受伊维菌素治疗后，所呈现的临床症状谱与接受伊维菌素治疗的高微丝蚴负荷人类患者相似。本实验模型的应用有助于优化人类伊维菌素治疗相关不良反应的管理方案。