Do crustacean allergies imply mollusk allergies in individuals with shellfish allergies?

From the Guidelines

Individuals with crustacean allergies do not necessarily have allergies to mollusks, as these are distinct categories of shellfish with different allergenic proteins. The primary allergen in crustaceans is tropomyosin, while mollusks contain different protein structures 1. According to the guidelines for the diagnosis and management of food allergy in the United States, the cross-reactivity between crustaceans and mollusks is relatively low, with 47% sensitization and 14% clinical reactivity 1. Many people who react to crustaceans can safely consume mollusks without experiencing allergic reactions. However, cross-reactivity can occur in some individuals, meaning they may be allergic to both types.

Some key points to consider:

• The allergenic proteins in crustaceans and mollusks are different, which supports the idea that an allergy to one does not necessarily imply an allergy to the other 1.
• Cross-reactivity can occur, but it is not universal, and the decision to try mollusks should be made under the guidance of an allergist 1.
• If you have a confirmed crustacean allergy but want to try mollusks, it's advisable to consult with an allergist first, who may recommend skin testing or a supervised food challenge to determine if you can safely eat mollusks.
• Always carry emergency medication like epinephrine auto-injectors (such as EpiPen or Auvi-Q) if you have any severe food allergies, and be cautious about potential cross-contamination in restaurants or food preparation areas where both types of shellfish might be handled.

From the Research

Crustacean and Mollusk Allergies

• Crustacean allergies do not necessarily imply mollusk allergies in individuals with shellfish allergies, as the relationship between the two is complex and not fully understood 2, 3, 4.
• Studies have shown that there is a high degree of cross-reactivity between different species of shellfish, including both crustaceans and mollusks 5, 6.
• However, the degree and pattern of cross-reactivity between different shellfish species can vary greatly, and some individuals may be allergic to only one type of shellfish 3, 4.

Diagnostic Challenges

• Diagnosing mollusk allergy in shrimp-allergic patients is still a complex process, and current diagnostic methods are often inadequate 4.
• Skin tests with fresh material may be more effective in detecting mollusk hypersensitivity than in vitro tests or commercial extracts 4.
• A clinical history, available diagnostic instruments, and/or tolerance tests should be used to support the decision to exclude mollusks from a shrimp-allergic patient's diet 4.

Allergen Cross-Reactivity

• Tropomyosin is a major allergen in both crustaceans and mollusks, and cross-reactivity between the two can occur 3, 6.
• However, the extent of cross-reactivity between crustaceans and mollusks is not fully understood and may vary depending on the individual and the specific species of shellfish involved 3, 4.
• Further research is needed to better understand the relationship between crustacean and mollusk allergies and to develop more effective diagnostic and treatment options for individuals with shellfish allergies 2, 4.