Molecular epidemiology of Anisakis spp. in blue whiting Micromesistius poutassou in eastern waters of Spain, western Mediterranean Sea

Abstract

The infection of blue whiting, Micromesistius poutassou, from the western Mediterranean, off the eastern coast of Spain, by larvae of Anisakis spp. was studied. Between April 2016 and April 2017, 140 fish were analyzed. Total epidemiological data show that the prevalence (P) of Anisakis spp. was 29.3%, the mean intensity (MI) was 1.80 and the mean abundance (MA), 0.53. Of the 74 larvae collected, 60.8% were type I and the remaining 39.2%, type II. Of the former, 91% were molecularly identified as A. pegreffii (P=19%; MI=1.44; MA=0.28), 2.2% as A. simplex s.s. (P=0.7%; MI=1.00; MA=0.01), while the rest (6.7%) showed a recombinant genotype between the two (P=2.1%; MI=1.00; MA=0.02). All the type II larvae analyzed were molecularly identified as A. physeteris (P=10.0%; MI=2.07; MA=0.21). Three fish (2.1%) were found to have larvae in the muscle, while 2 were found with 1 larva of A. pegreffii and 1 with 2 larvae (1 A. simplex s.s. and 1 A. pegreffii). Statistical analysis showed that the prevalence of Anisakis spp. in blue whiting from this geographical zone is higher in spring than in autumn (p<0.001), probably due to the greater size of the fish and that the probability of the fish being infected increases with increasing length and/or weight related with factors as diet shift, accumulation with age, higher food intake in larger fish, and others. It was also observed that the blue whiting is not infected in this zone by Anisakis until it is 1.6 years old, first by Anisakis type I ( ̴2.3 years) and later by Anisakis type II ( ̴2.7 years), probably due to the diet of the blue whiting changing with age, incorporating into its diet the paratenic/intermediate host species of these parasites. In any case, the public health authorities must continue to emphasize the need for suitable thermal treatment (freezing or cooking) of the fish prior to consumption since all the identified Anisakis species in blue whiting of this zone are pathogenic for man.