A recent study by Meglio et al. (1) showed a significantly higher prevalence of sensitization to snails in 101 mite allergic children, who never underwent specific immunotherapy (SIT) than in 82 similar subjects who underwent mite SIT in the previous 2 years.

The authors speculated the possible protective role of mite SIT against snail sensitization.

However, their methodological approach seems inappropriate in supporting this conclusion.

The skin prick test (SPT) used in the study seems unreliable in diagnosing snail sensitization, especially as only two children with positive reaction case histories after ingesting snails yielded negative SPT, which were positive in eight mite-allergic children who had either never eaten snails, apart from one child, or performed mite SIT.

Consistent with other studies on commercial SPT in food allergy, sensitivity was poor and the resultant clinical implications should be considered with caution.

In a study performed in 167 children with combined mite-snail allergy, commercial SPT was less sensitive than native extract SPT: sensitivity being 50 and 73.6%, respectively (2).

Clinical suggestions of a link between mite SIT and snail allergy (high prevalence of previous mite SIT in snail allergic patients, and appearance of recall urticaria at the mite SIT injection site during reaction to snail) were confirmed by evidence of cross-reactivity between mite and snail allergens, and by the appearance of snail specific IgE after mite SIT in subjects with negative reaction case histories to snail, who were not habitual snail eaters (2–4).

A recent food challenge study performed in children with combined mite-snail allergy, documented worsening clinical symptoms in food allergy to snail after mite SIT (5).

Besides the clinical implications, the induction/worsening of food allergy to snail by mite SIT represents a very interesting model which provides fuller understanding of the effect of SIT on inhalant-food cross-reactive allergens. Comparison of this model with the birch-apple model, where birch SIT seems to reduce food allergy to apple, is particularly interesting.

If the cross-reacting allergen is the (highly homologous) major allergen of inhalant and food (i.e. Bet v1/Mal d1) the high dose of allergen injected during SIT, seems to reduce sensitivity to this allergen in both target organs (6), whereas, if the dose of the cross-reactive allergen is very low (like in the mite-snail model), in susceptible subjects, SIT can induce new immunoglobulin (IgE) specificities (4).

The development of new IgE specificities during SIT has been described for other minor cross-reactive allergens present in the extract. As they belong to the same kind of inhalant allergen (pollen), the clinical role of this occurrence seems slight (7).

In conclusion, apart from the speculations about the effects of SIT in combined inhalant-food allergies, there is sufficient evidence pointing to mite SIT as a risk factor for severe reactions after snail ingestion. Snail avoidance is therefore strongly advisable in patients who undergo mite SIT.


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