[Secondary effects of the treatment of hypermicrofilaremic loiasis using ivermectin]

In the last ten years ivermectin appeared an efficient and safe alternative to diethylcarbamazine which is known to induce severe adverse reactions in loiasis, including encephalitis. After these results, large scale ivermectin treatments against onchocerciasis were carried out in Central Africa where loiasis is also endemic; and seven cases of severe reaction were reported in Cameroon since 1991, during these mass ivermectin treatments. In order to study adverse reactions in patients harbouring high load of Loa loa microfilariae (mf), we realized careful hospital based treatment in 112 patients with more than 3,000 mf/ml (ml) blood. Patients received once 200 micrograms ivermectin per kilogram at day 0 (D0). Clinical examination was made daily during the four following days (D1 to D4). Blood and urine samples were analysed before treatment and at D1 and D3. Lumbar puncture was made at D1 for 39 patients with more than 10,000 mf/ml; at D3 for the 49 following patients without consideration for the level of parasitaemia, and at D0 and D3 for ten voluntary patients. For analysis the patients were distributed in 3 groups according to initial parasitaemia: the first group included 50% out of the patients, those whose parasitaemia was fewer than 15,000 mf/ml blood; the second group included 25% patients whose parasitaemia was between 15,000 and 30,000 mf/ml; the third group included the last 25% patients whose parasitaemia was higher than 30,000 mf per ml blood. Adverse reactions were observed in 71% out of the patients. Symptoms described were fever, pruritus, headache, arthralgia. Most symptoms appeared 24 to 36 hours after treatment. Temperature increased significantly in group 3. Microfilaraemia decreased by 85% in the 3 groups during the 4 days following treatment. C-reactive-protein increased dramatically after treatment in all patients (p < 10(-4)). Some patients presented blood in urine in three groups but haematuria reached 35% of patients in group 3. Proteinuria is noted among 33% of all patients but 20% in group 1 and 2 versus 70% in group 3. Loa loa mf were observed in urine of half the patients, but in low amounts (< 10 mf per 50 ml urine). In cerebro-spinal fluid (CSF), some mf appeared at D1 or D3 in people heavily infected with Loa loa, reaching 80% of the patients of group 3. LP made at D0 in ten patients with parasitaemia higher than 30,000 mf/ml blood confirmed that CSF was naturally microfilaria free before treatment. One patient presented severe troubles with fever, asthenia and conscience troubles beginning at D3, reactive coma at D4, renal impairment with transitory anuria; progressive improvement in 2 weeks and complete recovery at D22; he presented 102 mf/ml CSF at D6. The study confirmed that ivermectin treatment is generally well tolerated. Among people with high Loa loa parasitaemia the symptoms after treatment are frequent but mild. However severe cases with conscience troubles are possible, and may occur in about 1% of subjects with more than 3,000 mf/ml blood. Severity of adverse reactions was linked to level of parasitaemia before treatment. The critical parasitaemia level which could lead to expect serious adverse effects seems to be 30,000 ml/ml blood. These informations should induce carefulness to carry out large scale treatments against filariosis in endemic areas of Loa loa.