Abstract
A histopathological survey was conducted to investigate the presence of microparasites in fish Archosargus probatocephalus in a river near Maceió, Brazil. Light microscope observations of fragments of gill showed the presence of small cysts containing numerous myxospores that were morphologically identified as Henneguya. Transmission electron microscopy observations further revealed several gill cells containing groups of prokaryotic cells within large cytoplasmic vacuoles. Each infected host cell displayed a single vacuole containing a variable number of Rickettsia-like cells (up to 11), some of which presented the dumbbell shape characteristic of binary fission. The Rickettsia-like cells were pleomorphic, without a nucleus and with chromatin dispersed in the cytoplasm. They had a thin electron-dense wall of Gram-negative type. The morphology of these prokaryotic was similar to those of the order Rickettsiales and was described as a Rickettsia-like organism. Histopathological evaluation showed that several vacuole membranes had a lysed appearance. Some had ruptured, thus allowing direct contact between the Rickettsia-like organism and the cytoplasm of the host cell. The rupturing of the branchial epithelium may have contributed towards reduction of the surface area of the gills, but it is not possible to say that this was the cause of the host's death.
Highlights
Occurrences of cell-dependent prokaryotic microorganisms such as Bacteria, Rickettsiae, Mycoplasma and Chlamydia in eukaryotes has been described worldwide
Light microscopy (LM) and transmission electron microscopy (TEM) Small fragments of tissues from different organs were checked under a light microscope, to detect any microparasites that might have been present
The cysts were surrounded by several layers of epithelial cells, some of which displayed cytoplasmic vacuoles containing small dense bodies that could not be identified in semithin sections (Figure 1A)
Summary
Occurrences of cell-dependent prokaryotic microorganisms such as Bacteria, Rickettsiae, Mycoplasma and Chlamydia in eukaryotes has been described worldwide These are commonly associated with differing pathogenicity in many geographical regions (Athanassopoulou & Karagouni, 2004; Azevedo, 1993; Azevedo et al, 2005; Birkbecka & Ringøb, 2005; Bower et al, 1994; Cusack et al, 2002; Fryer et al, 1990; Fryer & Lannan, 1994; Guo et al, 2004; Molloy et al, 2001; Turnbull, 1993; Villalba et al, 1999; Yuksel et al, 2006). The rickettsiosis were found to be especially important in salmon farms, where high mortality was observed (Branson & Diaz-Munoz, 1991; Chern & Chao, 1994; Corbeil et al, 2005; Cusack et al, 2002; Fryer et al, 1990; Guo et al, 2004)
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Schedule a callMore From: Revista brasileira de parasitologia veterinaria = Brazilian journal of veterinary parasitology : Orgao Oficial do Colegio Brasileiro de Parasitologia Veterinaria
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