Occurrence of, Anisakis larvae in Atlantic horse mackerel (Trachurus trachurus) sold in the city of Marrakesh, Morocco

Human anisakidosis is a parasitic infection caused by the ingestion of nematode larvae of the Anisakidae family contained in various organs of fish and cephalopods consumed raw or undercooked. The aim of this work was to detect and identify morphologically and genetically (PCR and sequencing) the nematode larvae present in both flesh and abdominal cavity of horse mackerel (Trachurus trachurus) which are widely consumed by the population of Marrakesh. For this purpose, 299 fish were purchased at the wholesale market in refrigerated conditions. They were originated from seven different landing ports along the Atlantic coast (Agadir, Dakhla, El Jadida, Essaouira, Mohammedia, Safi and Sidi Ifni). The fishes were analyzed from November 2017 to December 2019, and 4815 larvae were detected out of 294 positive horse mackerel. This resulted in a prevalence of 98.33% and a mean intensity of 16.38 larvae per fish. Horse mackerel from Mohammedia, El Jadida, Safi, Essaouira, Agadir and Sidi Ifni were more infested than those from Dakhla with a mean intensity of 25.29, 21.33, 18.88, 16.15, 15.90 and 13.86 larvae per fish, respectively, while that from Dakhla was the least infested with a mean intensity of 11.83. These results could be explained by the availability of primary intermediate hosts of Anisakis spp., such as crustaceans (shrimps), which are more abundant in the northern Moroccan Atlantic coast. Furthermore, we have recorded a higher infection in fish during warm seasons (spring and summer) than during cold ones. We also have noticed that as the distance from the fishing area increased, the larvae had more time to migrate from the abdominal cavity to the muscles. All detected larvae were identified morphologically as Anisakis type I and genetically as Anisakis simplex sensu stricto. Statistical analysis showed that the intensity of infection by Anisakis L3 larvae was positively correlated with the weight of horse mackerel and that origin had no impact on fish parasitism.