Cross-reactivity between terrestrial snails (Helix species) and house-dust mite (Dermatophagoides pteronyssinus). I. In vivo study

Clinical reports have suggested an unusual frequency in the number of patients with food allergy to snails who are also allergic to the house-dust mite (HDM). As allergy to HDM is one of the most frequent sensitizations in atopic patients of Western countries, evaluation of the relevance of the concomitant sensitization to Eermatophagoides pteronyssinus and to snails is an important consideration. To evaluate the responsibility of different snail components and of snail mites for inducing in vivo hypersensitivity in patients allergic to HDM, the in vivo reactivity of patients with clinical symptoms after ingestion of snails was assessed by skin prick tests with tests with extracts and hemolymph from four different Helix species snails, and extracts from the snail parasitic mite, Riccardoella limacum. In addition, to obtain epidemiologic data on cosensitization to HDM and snails in allergic patient, the frequency of snail sensitization and its relationship to HDM sensitization were determined in a population of 169 allergic children. All patients allergic to snails had positive skin prick tests to the snail extracts and none to R. limacum extract. The nunber of positive skin reactions did not significantly differ whatever the species, snail part, or heating procedure used. The strongest reactions were obtained with Helix pomatia (Burgundy snail extracts; 79% of the snail-sensitized children had sensitization to HDM; and 31% of the children allergic to HDM were found to be sensitized to snails. These results show that sanil components, and not the mite R. limacum, were responsible for the invivo hypersensitivity. These snail components reacting in vivo are present in different parts of snails, including the hemolymph. One-third of the children allergic to HDM were sensitized to snails without any previous ingestion of snails: this observation suggests that HDM was the sensitizing agent and that the cross-raction could be clinically relevant in countries where eating snails is common.