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Toxocariasis is a worldwide helminthic zoonosis due to the infection of humans by larvae of Toxocara canis, the common roundworm of dogs, or T. cati, a parasite of cats. Regarding treatment, only diethylcarbamazine (DEC) and mebendazole (MBZ), given daily orally (p.o.) for 21 days at 4 mg kg of body weight (bw)¹ and 25 mg kg bw¹, respectively, have to date demonstrated good efficacy (4).

Ivermectin has become the drug of choice for the treatment of onchocerciasis (1). This drug is also excellent for treating strongyloidiasis (5).

In 17 hypereosinophilic outpatients who attended the parasitology clinic at the University Hospital Purpan, Toulouse, France, the diagnosis of toxocariasis was based on the results from a Western blotting procedure using T. canis excretory-secretory antigens (3). Other helminthic diseases were ruled out by stool examination along with Baermann's method and by appropriate immunodiagnostic tests.

Two patients with a history of chronic hypereosinophilia were asymptomatic. The others presented with a clinical syndrome consistent with toxocariasis (2), namely chronic weakness (three cases), intermittent abdominal pain (six cases), intermittent diarrhea (three cases), and/or various allergy signs (seven cases). The duration of clinical picture and/or hypereosinophilia prior to the consultation was on average 18 months (standard error of the mean [SEM], 4.3; range, 3 to 72). The mean blood eosinophil count was 1.13 × 10⁹ cells liter¹ (SEM, 0.257; range, 0.44 to 4.5).

After informed consent was obtained, every patient was given p.o. a single 12-mg dose of ivermectin, corresponding on average to a rate of 193 µg kg bw¹ (range, 130 to 286). The mean time gap between drug intake and the checkup consultation was 7.9 weeks (SEM, 1.3; range, 4 to 24). Of the 15 symptomatic patients, 2 did not exhibit any clinical sign but still had an unchanging hypereosinophilia, 4 showed clinical improvement, and no effect was found for the remaining nine. Posttreatment mean blood eosinophil count was 1.0 × 10⁹ cells liter¹ (SEM, 0.15; range, 0.5 to 2.9). No significant difference (Wilcoxon's rank test) was noticed between pre- and posttreatment mean values of eosinophilia.

No significant correlation (Spearman's correlation test) was observed between the rate (micrograms per kilogram bw) of absorbed ivermectin or the posttreatment time gap on the one hand and the effect on clinical symptoms or the posttreatment mean eosinophil count on the other hand.

These results contrast with those for DEC and MBZ, both of which elicited in toxocariasis patients, on average 4 weeks after the treatment had ended, significant decreases in clinical signs and blood eosinophilia (4). Larger-scale controlled studies with placebo groups, therefore, have to be carried out to assess the real efficacy of ivermectin for the treatment of human toxocariasis. This zoonosis is indeed endemic in rural areas of Europe, and physicians could be tempted to use ivermectin, which has just been registered in the European Union, for the treatment of strongyloidiasis.