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

The infection of blue whiting Micromesistius poutassou from the western Mediterranean Sea, off the eastern coast of Spain, with larvae of Anisakis spp. was studied. Between April 2016 and April 2017, 140 fish were analyzed. Total epidemiological data showed that the prevalence of Anisakis spp. was 29.3% and the mean intensity 1.8. Of the 74 larvae collected, 61% were type I and the remaining 39%, type II. Of the former, 91% were molecularly identified as Anisakis pegreffii (P = 19.3%; MI = 1.4), 2.2% as Anisakis simplex s.s. (P = 0.7%; MI = 1.0), while the rest (6.7%) showed a recombinant genotype between the two (P = 2.1%; MI = 1.0). All the type II larvae analyzed were molecularly identified as Anisakis physeteris (P = 10.0%; MI = 2.1). Three fish (2.1%) were found to have larvae in the muscle, while two were found with 1 larva of A. pegreffii and one with two larvae (1 A. simplex s.s. and 1 A. pegreffii). Statistical analysis showed that the prevalence of Anisakis spp. in blue whiting was higher in spring than in autumn (P < 0.001), probably due to the greater size (and age) of the fish and related to factors as diet shift, accumulation with age and higher food intake. Analysis of the data suggested that blue whiting were first infected with Anisakis type I (mean age 2.3 years) and later with Anisakis type II (mean age 2.7 years), probably due to the diet changing with age, with the incorporation of 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.