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 hous e-dust mite (HDM). As allergy to HDM is one of the most frequent sensi tizations in atopic patients of Western countries, evaluation of the r elevance of the concomitant sensitization to Dermatophagoides pteronys sinus and to snails is an important consideration. To evaluate the res ponsibility of different snail components and of snail mites for induc ing in vivo hypersensitivity in patients allergic to HDM, the in vivo reactivity of patients with clinical symptoms after ingestion of snail s was assessed by skin prick tests with extracts and hemolymph from fo ur different Helix species snails, and extracts from the snail parasit ic mite, Riccardoella limacum. In addition, to obtain epidemiologic da ta on cosensitization to HDM and snails in allergic patients, the freq uency of snail sensitization and its relationship to HDM sensitization were determined in a population of 169 allergic children. All patient s allergic to snails had positive skin prick tests to the snail extrac ts and none to R. limacum extract. The number of positive skin reactio ns did not significantly differ whatever the species, snail part, or h eating procedure used. The strongest reactions were obtained with Heli x pomatia (Burgundy snail). Among the 169 prospectively tested childre n, 38 had a positive prick test to snail extracts; 79% of the snail-se nsitized children had sensitization to HDM; and 31% of the children al lergic to HDM were found to be sensitized to snails. These results sho w that snail components, and not the mite R. limacum, were responsible for the in vivo 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 th at HDM was the sensitizing agent and that the cross-reaction could be clinically relevant in countries where eating snails is common.