There is strong IgE cross-reactivity between allergens from all crustacea. The most important allergen in these species is tropomyosin and DeWitt et al. (2004) [1536] reported that recombinant Pen a 1 bound 94% of the IgE from the 6 crustacea specific sera. As tropomyosin is strongly conserved in sequence with more than 99% identity amongst penaeoid shrimps and 92% identity between more distantly related crustacea such as a penaeoid shrimp (Farfantepenaeus aztecus) and a crab (Charybdis feriatus), allergy to crustacea is generally treated as a single allergy. DeWitt et al. (2004) [1536] also showed specific IgE binding to recombinant Pen a 1 and seven invertebrate extracts with 9 sera. 6 sera bound extracts from crustacea most strongly, 2 bound dust mite extract more strongly and one serum showed similar binding with both extracts. rPen a 1 bound 94% of the IgE from the 6 crustacea specific sera and gave 50% inhibition of the binding of extracts at about 0.1 µg/ml. However, the crab used by DeWitt et al. (2004) was Cancer pagurus.

Leung et al (1998) [1554] reported the percentage of amino acid identity of crab Cha f 1 with the known allergens Met e 1 from shrimp, Pan s 1 from spiny lobster and Hom a 1 from Homarus americanus as 90%, 91%, 92%. Also the tropomyosins from Homarus americanus slow muscle, from fruit fly and from chicken were 96%, 69% and 60% identical respectively. As might be expected at this level of similarity, these authors found that IgE from the sera from 10/10 crab allergic subjects bound the recombinant shrimp and lobster tropomyosins (rMet e 1, rPan s 1 and rHom a 1).

Chiou et al. (2003) [1689] studied IgE cross-reactivity of 67 sera from patients allergic to multiple allergens with 36 Pharmacia allergens. There was a significant correlation of reactivity between crab, Cancer pagurus, (F23) and shrimp, Pandalus borealis (F24). IgE from 27 sera bound crab (F23), IgE from 28 bound shrimp (F24) and IgE from 20 sera bound both allergens. Inhibition studies on IgE binding in 15 sera gave an inhibition of >50% between 3 shrimp and cockroach reactive sera, an inhibition of >50% between 11 shrimp and crab reactive sera, and an inhibition of >50% between 4 crab and cockroach reactive sera.

Leung et al (1996) [1557] report that 9/9 sera from shrimp allergic patients reacted to mud crab (Scylla serrata) and lobster (Panulirus homarus) extracts. Lehrer et al. (1985) [1706] used crossed immunoelectrophoresis to show that of the 7 allergens detected from white shrimp, 5 cross-reacted with crayfish, 3 with lobster and 1 with crab extract. Two precipitins appear to be common crustacea allergens and were present in shrimp, crayfish, lobster and crab. Similarly, skin prick tests and RAST with extracts of shrimp, blue crab (Callinectes sapidus), crawfish (Procambarus clarkii), and lobster (Panulirus sapidus) were highly correlated (Daul et al., 1987 [1574]).

There is also IgE cross-reactivity between crustacea and insects, gastropods, bivalves and cephalopods (van Ree et al. 1996 [1609]; Leung et al 1999 [1557]; Goetz & Whisman, 2000 [1594]). This is believed to be due to allergenic tropomyosins. Fernandez et al. (2003) [1539] demonstrated IgE binding and SPT reactivity to shrimp in subjects sensitised by insect and mite allergens without prior exposure to shrimp.

In contrast to the observed cross-reactivity in IgE binding between arthropods and mollusks, clinical cross-reactivity is less common and some but not all crustacea allergics can tolerate mollusks (Leung et al (1996) [1557]; Ishiwara et al. 1998 [1584]; Ishiwara et al. 1998 [1582]).

As expected, Helbling et al. (1996) [1727] did not demonstrate any IgE cross-reactivity between finfish and crab (Callinectes sapidus), crawfish (Procambarus clarckii), lobster (Palinurus argus) or shrimp (Litopenaeus setiferus). 

Occupational allergy to crustacea including snow crab has been reported (Cartier et al. 1986 [1591]; Desjardins et al. 1995 [1561]; Ortega et al. 2001 [1592]). Cartier et al. 1986 [1591] used both extracts of meat or snow crab (Chionoecetes opilio) cooking water to demonstrate sensitisation by SPT. Cartier et al. 2004 [1610] report that the prevalence of sensitisation in different crab plants varied from 50% (n=19) to 15% (n=16) and the prevalence of certain or highly probable crab asthma varied from 50% (n=19) to 9% (n=3). A preliminary report describes immunoblotting with these sera (Hefle et al. 1995 [1761]) and reported multiple IgE- reactive proteins of 25 to 45 kDa and 5 IgE proteins of 14 kDa or less in snow crab meat and cooking water extracts. 5 of 18 sera showed IgE binding to single bands at 38 to 41 kDa. Wu et al. (2002) [1734] suggests that exposure to crab as an aerosol can be associated with atopic dermatis. Such aerosols may be responsible for occupational allergies to crab.

Lin et al. (1993) [1575] found clear evidence for a 39 kDa allergen which is an arginine kinase from Japanese blue crab, Portunus trituberculatus.