Preliminary Data on the Occurrence of Anisakis spp. in European Hake (Merluccius merluccius) Caught Off the Portuguese Coast and on Reports of Human Anisakiosis in Portugal

Abstract

Parasitic nematodes of the genus Anisakis are among the most important biological hazards associated with seafood. A survey of Anisakis spp. in European hake (Merluccius merluccius) was undertaken as this species is a staple of the Portuguese diet. Moreover, a literature review of cases of anisakiosis reported from Portugal, a country with one of the highest levels of fish consumption in the world, was also carried out. Seventy-five European hake caught in the Atlantic Ocean off the northern coast of Portugal were analyzed to determine the infection levels and site distribution of Anisakis spp. Isolated nematode larvae were identified to species level by molecular analysis. Two sets of samples were collected. Firstly, a total of 46 Anisakis spp. L3 larvae were collected with a prevalence of 76.7% (95% CI 61.5–91.8%) and intensity (mean ± SD, range) of 2.0 ± 1.2 (1–5). Most larvae were found on the liver (45.7%) and on the gonads (32.6%), but none in the muscle. The molecular analysis showed the presence of both A. simplex s.s. (70%) and A. pegreffii (30%). For the second sample, analyzed using the UV-Press method, a total of 473 Anisakis spp. were found, with a prevalence of 95.6% (95% CI 89.5–100.0%), intensity (mean ± SD, range) of 11.3 ± 9.7 (1–41), density of 0.05 ± 0.04 (0–0.16) worms/muscle weight in g, and density of 0.54 ± 0.50 (0–2.53) worms/viscera weight in g. Surprisingly, only three very recent cases of human anisakiosis in Portugal have been reported in the literature. Data from this study contribute towards an updating of the existing epidemiological picture in an area characterized by very high seafood consumption and changing eating habits.

Anisakid Nematodes and Potential Risk of Human Anisakiasis through the Consumption of Hake, Merluccius spp., Sold Fresh in Spanish Supermarkets

“…The analysis of the fish catching season on larvae parasitization, mainly on Anisakis larvae showed a similar pattern in the three populations of hakes, with the autumn-winter period reaching the highest parasitization parameters, prevalence and mean abundance, compared to the spring-summer period, with or without statistically significant differences. However, these results are not in accordance with those reported in previous studies in this and other fish species previously analysed, which reported mainly, the highest parasitization parameters during the spring season [12,18,22,36,44,45]. Only a few studies reported a higher parasitation in fish caught during the autumn season, such as in the silver hake [1,12].…”

“…The very high global prevalence of Hysterothylacium and Anisakis type I larvae in the samples of European Atlantic hake and silver hake, as well as the low prevalence in the sample of European Mediterranean hake stands out. These results are in agreement with the most of the previous studies carried out on samples of the European Atlantic hake [12,22,25,27,[31][32][33][34][35][36], the silver hake [37], and the European Mediterranean hake [12,25,33,[38][39][40]. In this last case, the studies carried out in the same Mediterranean subdivision, FAO 37.1.1-Balearic, were taken into account, with the exception of the study carried out by Valero et al [26], which found a higher prevalence of parasitization in this area.…”

“…Fish size, length and weight, influenced the Anisakis larvae parasitization parameters of the three hake population analysed, with the only exception being the prevalence in the silver hake. This positive relation between the size (age) of the fish and the increase of parasitization has been reported particularly in the case of hake analysed in various fishing grounds of the Atlantic Ocean and the Mediterranean Sea [12,22,[25][26][27][28]30,33,34,36,38,40], although this is not a universal phenomenon in fish, and this correlation might even be negative [22].…”

Seafood safety and food‐borne zoonoses from fish

“…There are very few reported cases of anisakiosis in Portugal (Santos et al., 2022 ). The first case was reported in 2017 by Carmo et al.…”

“…Furthermore, dead Anisakis larvae may be allergenic to previously sensitised individuals. Hake gonads are a popular Portuguese dish and this area of the fish is frequently parasitised by Anisakis (Santos et al., 2022 ). The factors outlined above indicate that the Portuguese population is at risk of exposure to this parasite.…”