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

Abstract

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 Dermatophagoides 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 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 patients, 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 number 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). Among the 169 prospectively tested children, 38 had a positive prick test to 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 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 that HDM was the sensitizing agent and that the cross-reaction could be clinically relevant in countries where eating snails is common.

Allergen cross‐reactivity between house‐dust mites and other invertebrates

“…Some terrestrial snails have a mite parasite, Riccardoella limacum, but it is not taxonomically close to HDM. SPT with R. limacum extract in snail-sensitized patients gave no skin reactions; thus, it is not likely to be responsible for the sensitization (129).…”

“…Positive covariation of snail and HDM sensitization has been demonstrated in some (129,130), but not all tested populations (131).…”

“…This is further con®rmed by clinical ®ndings in those HDM-sensitized patients who have developed allergic reactions to snails while claiming never to have eaten them before (26, 134). Half of the patients with allergy to terrestrial snails also react to marine snails (129). Some terrestrial snails have a mite parasite, Riccardoella limacum, but it is not taxonomically close to HDM.…”

“…Sensitization to snail demonstrated by SPT appeared in 31% of HDMallergic children in an unselected population (129). About 50% of these children had a positive open labial food challenge with snail, even though they all denied having eaten snails before (129). At the start of HDM IT, 76% of the patients showed sensitization to snail (compared with 13% in a group of Parietariaallergic patients) (26).…”

“…In several reports of HDM±snail allergy, the patients had received IT for HDM, and, after snail ingestion, urticaria, erythema, and itch often appeared at the sites of previous IT injections (26,122,129,132,133,135). IgE against snail seems to increase in these IT patients, while IgE against HDM remains unaffected (26).…”