BREVIMULTICAECUM SP. (NEMATODA) LARVAE IN LIVER OF FISH GYMNOTUS INAEQUILABIATUS FROM PANTANAL REGION BRAZIL: LIVER PATHOBIOLOGY AND INFLAMMATORY RESPONSE

Gymnotus inaequilabiatus is a fish of great importance in Pantanal region (Brazil). It is used as livebait for collecting other fish species of commercial value and is one of the preferred prey for Caiman yacare. G. inaequilabiatus is paratenic host for the nematode Brevimulticaecum sp. and C. yacari is the definitive host where the adult parasites can be find in the intestine. In two occasions, one in the flood season and one in the dry period, ββ specimens of G. inaequilabiatus were sampled (mean total length ± standard deviation, SD: γ1.88 ± β.54 cm). Larvae of Brevimulticaecum sp. were encountered in likely all the visceral organs, but, this investigation was focused on liver. Twenty-one livers (95%) harboured Brevimulticaecum sp. larvae, with an intensity of infection ranging from 4 to γ4γ larvae (mean ± SD: 71.00±9γ.β8 larvae for liver). In livers with high number of nematode larvae the vast majority of the hepatic tissue was occupied by the parasites. Most Brevimulticaecum sp. larvae were encapsulated on the surface of the liver, enclosed by a granulomatous response involving the peritoneal visceral serosa. The cellular immune response within liver was assessed by histological methods and transmission electron microscopy. The wall of the capsule was composed of two layers: the innermost, which was adjacent to the nematode, consisted of host connective tissue, mainly collagenous fibres, whilst the outer layer consisted mainly of mast cells (MCs) and macrophage aggregates (MAs). In infected livers, hepatocytes, notably those in close proximity to larvae, showed degenerative changes, i.e. swelling and hydropic degeneration. By comparison, hepatocytes in uninfected liver or in regions away from the larvae appeared normal. Emphasis will be placed on the role of MCs and MAs as important components of the host’s inflammatory response.