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

Abstract

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 (p<0.05) in all animals following ivermectin treatment with reductions as high as (89.9%) recorded; while no significant drop was observed in the control animals. Apart from haemoglobin (Hb) levels which recorded a significant (p = 0.028) drop post treatment, all other haematological and biochemical parameters did not show any significant changes (p>0.05). All animals became withdrawn 48 hours after IVM administration.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 incr...

Evaluation of in vitro culture systems for the maintenance of microfilariae and infective larvae of Loa loa

“…Microfilaraemic loads were determined microscopically on thick films. Calibrated thick blood smears were prepared by spreading a 50 μl venous blood sample from a 75 μl non-heparinised capillary tube, onto a clean slide over an area of 1.5 × 2.5 cm [ 16 ]. After drying, films were dehemoglobinized and stained with Giemsa.…”

Mouse models of Loa loa

“…L. loa naturally infects an endangered species of monkey, the drill ( Mandrillus leucophaeus ), endemic to Central Africa. As a surrogate non-human primate model, the life cycle of L. loa can be maintained via experimental infection of splenectomised baboons 16,17 , a model which has recently been utilised to initiate exploratory pathology studies of IVM-associated neurological SAE 18,19 . This model has also generated adult and mf parasitic stages for a range of ex vivo studies.…”

Impact of repeated annual community directed treatment with ivermectin on loiasis parasitological indicators in Cameroon: Implications for onchocerciasis and lymphatic filariasis elimination in areas co-endemic with Loa loa in Africa

“…Given the fact that in the clinical and community trials it was demonstrated that a single dose of ivermectin can lead to 80–90% reduction of L . loa microfilaraemia [ 15 , 16 ], one could have expected to have a lower fraction of individuals still harbouring L . loa mf.…”

“…loa presents an intriguing vicious cycle that was illustrated recently with the development of an animal model of L . loa encephalopathy [ 15 , 43 ]. Ivermectin is highly efficacious in clearing the L .…”

“…It has been demonstrated that a single oral dose of ivermectin brings about a dramatic decrease in the load of Loa loa microfilariae (mf) and even an improvement in some clinical signs related to the infection [ 8 – 15 ]. The impact of repeated large-scale 3-monthly treatment with ivermectin for over a year on the transmission of loiasis in a forest village in south Cameroon where loiasis was highly endemic, with a prevalence above 30% was investigated by Chippaux and colleagues [ 16 ].…”