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Experimental demonstration of pathogenic potential of Anisakis physeteris and Anisakis paggiae in Wistar rats

Abstract:

Anisakis morphotype I is the principal etiologic agent of human anisakiasis, with differences in pathogenicity found between the Anisakis simplex s.s. and A. pegreffii species; however, the role of morphotype II larvae in this illness is not well understood. The purpose of this study is to verify the ability of morphotype II larvae to invade tissues via the experimental infection of Wistar rats, an animal model which simulates infection in humans. In the in vivo assay, 7.1 % (4/56 L3 morphotype II) showed pathogenic potential, defined as the capacity of the larvae to cause lesions, attach to the gastrointestinal wall or penetrate it. Two of these larvae, one of A. physeteris and one of A. paggiae, penetrated the stomach wall and were found within the abdominal cavity, with the first one producing a small lesion with blood vessel breakage. The majority of the L3 larvae of morphotype II were found in the intestine (51.8 %; 29/56) with the caecum being the least frequent location (8.9 %; 5/56). In contrast, 44.0 % (11/25) of the morphotype I larvae demonstrated pathogenic potential. Isoenzyme electrophoresis, PCR-RFLP of ITS1-5.8 s-ITS2 and PCR-sequencing of the cox2 mitochondrial gene were used to identify these larvae as A. physeteris (42.9 %), A. paggiae (30.3 %) and A. brevispiculata (1.8 %). Although the morphotype II larvae of A. physeteris and A. paggiae have lower pathogenic potential than morphotype I larvae of A. simplex s.s. (93 and 91 % lower, respectively), they may still be implicated in human anisakiasis, as they are capable of attaching to and penetrating the gastrointestinal wall of animals, demonstrating a similar pathogenicity to that of A. pegreffii. The techniques used for the identification of species reveal a great genetic heterogeneity of A. paggiae and A. physeteris, suggesting the existence of sibling species.