toxocariasis resulting in seeming allergy

toxocara canis is an intestinal nematode affecting dogs and cats that causes human infestations by ingestion of embryonated eggs excreted in dogs' faeces. humans are transport hosts, in whom the larvae do not develop to adult worms, but may migrate to various tissues and organs, and survive for several years, giving rise to several clinical symptoms, which include allergy-like presentations. we report three cases presenting as dermatitis, rhinitis, asthma, and conjunctivitis which were diagnosed and unsuccessfully treated as allergy. the correct diagnosis was established after detecting anti-toxocara antibodies by western blotting. all clinical symptoms showed improvement after starting treatment with mebendazole and subsequent courses of the antiparasitic drug resulted in full recovery. this suggests the possible role of toxocara canis in inducing chronic symptoms of allergic type. this is particularly important for asthma, where it has been demonstrated that toxocara canis infection causes allergic inflammation in the lungs associated with bronchial hyperreactivity. on the other hand, in our patients with asthma and with dermatitis the positive results from allergy tests were a confounding factor in delaying the correct diagnosis, which was finally obtained by the detection of antibodies to toxocara canis.