Anisakis - immunology of a foodborne parasitosis

Anisakis species are marine nematodes which can cause zoonotic infection in humans if consumed in raw, pickled or undercooked fish and seafood. Infection with Anisakis is associated with abdominal pain, nausea and diarrhoea and can lead to massive infiltration of eosinophils and formation of granulomas in the gastrointestinal tract if the larvae are not removed. Re-infection leads to systemic allergic reactions such as urticarial or anaphylaxis in some individuals, making Anisakis an important source of hidden allergens in seafood. This review summarizes the immunopathology associated with Anisakis infection. Anisakiasis and gastroallergic reactions can be prevented by consuming only fish that has been frozen to -20°C to the core for at least 24 hours before preparation. Sensitization to Anisakis proteins can also occur, primarily due to occupational exposure to infested fish, and can lead to dermatitis, rhinoconjunctivitis or asthma. In this case, exposure to fish should be avoided.

Allergenic activity of Pseudoterranova decipiens (Nematoda: Anisakidae) in BALB/c mice

BACKGROUND

Anisakis simplex is the only fishery-product associated parasite causing clinical allergic responses in humans so far. However, other anisakids, due to the presence of shared or own allergens, could also lead to allergic reactions after sensitization. The aim of this study was to determine if Pseudoterranova decipiens belonging to the family Anisakidae has allergenic activity and is able to induce sensitization after oral administration in a murine (BALB/c mice) model.

RESULTS

The ingestion of A. pegreffii proteins by BALB/c mice, which had been previously sensitized by intraperitoneal inoculation with the corresponding live L3 larvae, triggers signs of allergy within 60 min, whereas P. decipiens did to a lesser extent. Beside symptoms, allergic reactions were furtherly supported by the presence of histamine in sera of sensitized mice. Specific IgG1 and IgE responses were detected in sera of all sensitized mice from week four. Specific IgG2a response was detected in sera from mice sensitized to P. decipiens. After polyclonal or specific activation with anti-CD3/anti-CD28 or antigens, respectively, splenocytes from mice infected i.p. with A. pegreffii or P. decipiens larvae showed significantly higher production of IL-10 than naïve mice. After stimulation with specific antigens, significantly higher IL-5 and IL-13 amounts were produced by specific antigen stimulated splenocytes than by the naïve cells; only P. decipiens proteins induced IFN-ɣ.

CONCLUSIONS

The overall results suggest that infection with P. decipiens can sensitize mice to react to subsequent oral challenge with anisakid proteins, as described for A. simplex (sensu stricto) and A. pegreffii infections. The results show that anisakid proteins induce a dominant Th2 response, although P. decipiens could also induce a mixed type 1/type 2 pattern.

Anisakis haemoglobin is a main antigen inducing strong and prolonged immunoreactions in rats

Anisakis simplex larvae are well known to cause gastrointestinal and allergic manifestations after ingestion of parasitized raw or undercooked seafood. The antibody recognition dynamics against the components of Anisakis larval antigen after primary and re-infection with Anisakis live larvae remain unclear. For this study, immunoblot analyses of serum IgG, IgE, and IgM against Anisakis larval somatic extract were performed in rats that had been orally inoculated with A. simplex live larvae. Multiple antigen fractions were recognized after primary infection. Their reaction was enhanced after re-infection. Antibody recognition was observed for 12 weeks after re-infection. The fraction of approximately 35 kDa contained a main antigen that induced strong and prolonged immunoreactions in IgG and IgE. The antibody reaction to this fraction appeared to be enhanced after inoculation of larval homogenates. This fraction was heat tolerant with boiling for 30 min. The fraction was spotted by immunoblotting after two-dimensional electrophoresis and was identified as Anisakis haemoglobin (Ani s 13) using mass spectrometry analysis. The amino acid sequences of haemoglobin mRNAs from two A. simplex sensu stricto and one Anisakis pegreffii were identified by RACE-PCR. They differed from those of two isolates of Pseudoterranova decipiens and A. pegreffii. Results of this study show that Anisakis haemoglobin, which is known to be a major allergen of A. simplex, induces strong and prolonged immunoreaction in rats. This report is the first to show the amino acid sequence variation of Anisakis haemoglobin mRNA between A. simplex sensu stricto and A. pegreffii.

Immune reactions and allergy in experimental anisakiasis

The third-stage larvae (L3) of the parasitic nematode, Anisakis simplex, have been implicated in the induction of hyperimmune allergic reactions in orally infected humans. In this work, we have conducted a review of an investigation into immune reactions occurring in animals experimentally infected with A. simplex L3. The patterns of serum antibody productions in the experimental animals against excretory-secretory products (ESP) of A. simplex L3 contributed to our current knowledge regarding specific humoral immune reactions in humans. In our review, we were able to determine that L3 infection of experimental animals may constitute a good model system for further exploration of immune mechanisms and allergy in anisakiasis of humans.

The time course of biological and immunochemical allergy states induced by anisakis simplex larvae in rats

Oral infection by Anisakis simplex third stage larvae (L3) frequently gives rise to an allergic response. To comprehend the allergic and immune responses induced by L3, we investigated the kinetics of specific antibody isotype expression and the time course of biological and immunochemical allergy states using sera prepared from rats orally infected with L3 twice, with an interval of 9 weeks between infections. Biological and immunochemical allergy states were analysed by RBL-2H3 exocytosis and by indirect ELISA for IgE, respectively. The peak IgM at reinfection (RI) was comparable or similar to that at primary infection (PI) both in levels analysed by indirect ELISA and in antigen recognition analysed by Western blot. IgG1 and IgG2a levels were higher and showed accelerated kinetics after RI vs. after PI. However, the level of IgG2b was substantially lower than that of IgG2a. Peak immunochemical and biological allergy states for RI were higher and were reached faster than those for PI. The peak biological allergy state was observed at 1 week postreinfection and this occurred sooner than that for the peak immunochemical allergy state found at 2 weeks postreinfection. Our analysis of the relationship between specific IgE avidity and biological allergy state did not show any meaningful correlation. These results suggest that the allergic response induced by L3 oral infection is predominantly caused by reinfection and that this is accompanied by an elevated IgM level, which further suggests that the biological allergy state might not be related to specific IgE avidity.

Usefulness of currently available methods for the diagnosis of Anisakis simplex allergy

BACKGROUND

Serodiagnosis of anisakiosis and Anisakis allergy is difficult since many Anisakis antigens show cross-reactivity complications. In the present study, we assess the usefulness of the major immunologic methods currently available for the diagnosis of Anisakis allergy.

METHODS

Four tests (skin prick test, CAP-FEIA system, Western blotting, and an antigen-capture ELISA using O-deglycosylated antigen bound by the monoclonal antibody UA3) were applied to Anisakis-free subjects and subjects with confirmed Anisakis allergy.

RESULTS

The skin prick test, CAP-FEIA, and the antigen-capture ELISA identified Anisakis allergy sera with 100% sensitivity, while Western blotting showed 96%/ sensitivity. The antigen-capture ELISA also showed 100% specificity, but CAP-FEIA showed a specificity of only 50%. In Western blotting, none of the bands detected were specific for either Anisakis-free or Anisakis allergy subjects. The skin prick test was not applied to the Anisakis-free subjects, so its specificity could not be determined.

CONCLUSIONS

On the basis of these results, we suggest that the most appropriate procedure for diagnosis of Anisakis allergy suspected on clinical grounds is the antigen-capture ELISA using UA3, or, alternatively, a preliminary skin prick test with a positive result subsequently confirmed by UA3-ELISA.

Usefulness of early serial measurement of specific and total immunoglobulin E in the diagnosis of gastro-allergic anisakiasis

BACKGROUND

Sensitization to Anisakis simplex (A. simplex) has been documented to produce severe allergic reactions following ingestion of mainly raw or under-cooked parasitized fish. False positive skin prick tests (SPT) or specific IgE against this nematode and cross-reactivity restricts diagnosis. Gastric anisakiasis and gastro-allergic anisakiasis occur if fish is parasitized by live A. simplex

OBJECTIVE

To investigate if serial serological analysis could be useful in the diagnosis of acute parasitation by this nematode.

METHODS

We included 41 patients who experienced an allergic reaction and/or abdominal symptoms after ingestion of raw or undercooked fish and displayed specific IgE against A. simplex. Total and specific IgE were determined two times: in the 24-h period after onset of clinical symptoms and after 1 month. SPTs were performed against A. simplex and implicated fish. A fibre optic gastroscopy was performed in 22 patients.

RESULTS

Median total IgE was 80.0 (Interquartile range [IQR] 41.5-186.5) kU/L in the first evaluation and 247.0 (IQR 96.5-649.5) kU/L after 1 month. Median specific IgE against A. simplex was 11.4 (IQR 7.1-33.5) kU/L in the first 24 h and 36.8 (IQR 19.5-79.5) kU/L after 1 month. A rise of total IgE was observed in 35 of 41 patients (P<0.00001) and a rise in specific IgE against A. simplex in 37 of 41 patients (P<0.00001). Mean percentage increment was 392% (215-571%; 95% confidence interval [CI]) for total IgE and 339% (177-502%; 95% CI) for specific IgE. In nine of 22 gastroscopic examinations at least one larva, identified as A. simplex, could be detected by our microbiology service. In this group (n = 9) a rise of total and specific IgE was detected in eight patients (89%) (P = 0.02).

CONCLUSIONS

We consider a rise of total and specific IgE in the first month after an allergic reaction as a useful tool in the diagnosis of gastro-allergic anisakiasis (together with patient's history), even if the parasite cannot be seen with fibre optic gastroscopy. The important rise of total and specific IgE against A. simplex can be considered as a reaction induced by the live parasitizing larva in the context of a polyclonal immunological stimulation.

Isotype-specific immune responses in murine experimental anisakiasis

A murine experimental model of anisakiasis has been developed in BALB/c and C57BL/10 mice orally inoculated with an Anisakis simplex living third stage larva (L3) in order to investigate isotype-specific immune responses against excretory-secretory (ES) products and crude extracts (CE) from L3. Specific antibody production showed similar patterns against both ES and CE antigens with higher levels against the latter. The dynamics of the production showed the earliest responses in BALB/c, in which antibodies were principally of the immunoglobulin (Ig)M isotype. Responses to the IgG1 subclass were mainly produced in the C57BL/10 strain. Levels of IgG2a were practically undetectable. With sera from C57BL/10 mice high levels of the IgG2b isotype were detected. A slight IgG3 response was only detected against the CE antigen in the C57BL/10 strain by the end of the experiment and IgA responses were very low. Humoral responses against A. simplex antigens are different depending on individual characteristics and thymus-independent epitopes might be represented into A. simplex antigens and their stimuli could be different regarding the murine strain used.

Enzyme-linked immunosorbent assay, immunoblot analysis and RAST fluoroimmunoassay analysis of serum responses against crude larval antigens of Anisakis simplex in a Spanish random population

The results obtained in a study of seroprevalence by means of ELISA and immunoblot with crude larval extracts of Anisakis simplex using 1008 human sera from Spanish people showing no clinical suspicion of anisakidosis are given. For the evaluation of the results obtained by ELISA the Diagnostic Index (DI) was used, as the ratio between the optical density resulting from the test serum and the optical density of the negative control. Forty-seven sera showed DIs between 1.5 and 2, and 14 sera were greater than 2. After comparison of the immunoblot analysis with the immunorecognition pattern of a human anisakidosis reference serum, a diagnostic criterion could be established for those sera that, at a 1/100 dilution, showed a DI by ELISA greater than 1.5. Seven of 14 selected sera with DIs in ELISA higher than 1.3 showed anti-Anisakis specific IgE antibodies by RAST fluoroimmunoassay.