Essay: Ultrastructure of Acanthocephala infection in Marine fishes

Introduction
Histopathology is a microscopic study; it is used to assess the manifestation of diseases and evaluation of the organ structure. This is reflecting the morphological structure of the cells and tissues. The parasites are an important group of pathogen causes infection and diseases to the fish both in fresh water and marine fishes. Formerly many authors have related to the extent of histopathology in the gut caused by these parasitic worms to factors such as the attachment apparatus, parasite size relative to host size and movement within the alimentary tract (Bullock, 1963; Chaicharn and Bullock, 1967, Wanstall, Robotham and Thomas, 1986; Wanstall, Thomas and Robotham 1988; Szalai and Dick, 1987; Taraschewski 1988, 1989a). Amina El-Mansy et al. (2011) has been studies the histopathology of tissues of different cultured fishes (Cyprinus carpio, Clarias gariepinus, Oreochromis aureus, Sarotherodon galilaeus and Tilapia zillii) due to different helminthes had been investigated. But, in the case of the present study was carried out the various species of marine fishes infected with the several Acanthocephalan species. The direct effect of helminth parasites mainly depend on their attachment organs. Occurrence of the disease conditions particularly due to parasites has become a major constraint in aquaculture and captive fisheries (Bondsd-Reantaso et al., 2005).
Acanthocephalan has been frequently reported in the intestines of wild fresh water and marine fishes in throughout world. Selective pressures of parasites alive in the lumen of the gastrointestinal tract, where physical disturbance in the form of peristalsis and food movement can exert powerful drag on attached parasites (Poulin, 2009). Acanthocephalans in particularly have developed a proboscis armed with hooks that anchor to the gut of their final host (Taraschewski, 2000). The infected fish intestines suffer irreversible mechanical damage due to the attachment of the acanthocephalan armed proboscis which also affects the architecture of the intestinal tissues leading to pathological changes. Although, there are several studies particularly the parasitic morphology and histopathological investigations on most helminthes species that had been described are still scanty (Castro, 1992). The Endoparasitic helminths often induce the inflammation and modification of the structure and function of infected tissues. According to Sharkey (1992), the inflammation consists of a complex series of homeostatic mechanisms involving the immune, nervous and circulatory systems in response to tissue injury or infection. There are several published records on the essential role of enteric immune cells in inflammatory processes caused by parasitic helminths (Dezfuli et al., 2000a, 2002a, b, 2003b; Bosi et al., 2005).
The pathological effects might be localized around individual worms in low infection, but in the high parasite load, total destruction of the tissue architecture due to the occurrence of the collective pathological changes. Loss/degeneration of intestinal villi, formation of the granular tissues and capsule formation associated with host immune responses that seriously affect animal’s digestive and absorptive efficiency. In heavy infections they cause occlusion of the gut and invasion and migrate into uncommon locations (Nickol, 2006). The pathogenesis consequences of the parasitized fishes are well documented and serve as evidence that the parasites are one of the main causes of fish mortality.
Schmidt and Roberts (2005) described that acanthocephalan lack a digestive tract; they absorb nutrients directly from the lumen of the host intestine. Absorption occurs across the tegument of the parasite. Marcogliese, (2004) also reported that the parasites affect the fish health, growth, behavior, fecundity and mortality and also regulate host population dynamics and their community structure. Acanthocephalan parasites of fishes live either as adults in the intestine or as larvae (post-cystacanths) in fish tissues. The ultrastructure of the infected fish intestine has been well documented in this chapter. The fact that the parasite has not been investigated in great detail in Marine fishes Tamil Nadu coast. Therefore, this study aimed to evaluate the histological lesion observed through light microscope of the Acanthocephala infection on the host fishes.
Materials and Method
The Acanthocephala were collected from the intestine of naturally infected fishes. The infected intestine samples cut were preserved in the 10 % buffer formalin for histopathological study. The selected samples were stored in 70 % ethanol, dehydrated in ethanol, embedded in paraffin wax and 3 ??m sections were obtained using a rotary microtome. The sections were stained with Harris Haematoxylin and Eosin according to (Coolidge and Howard 1979). The stained tissues were examined under a compound microscope (40?? magnification), and digital images of histological features were obtained using the Lucia (Laboratory Imaging, www. forensic. cz/ en/ products) screen measurement system.

Results
The examination of the intestine of host fishes (Caranx ignobilis Seriolina nigrofasciata Thunnus albacares Nibia maculate) revealed that presence of heavy infection with the Acanthocephalan . The actual trunk of the worms is also visible nestled between microvilli. Again ‘gap’ is visible in each of these figures but this is thought to be an artifact. The higher magnification view of the proboscis in Figure 6e illustrates a proliferation of erythrocytes and leukocytes surrounding the area of proboscis attachment (Fig. 6f).
The praesoma of the acanthocephala extended through the intestinal wall Fig.. and the proboscis was enclosed in a nodule within the mesentery surrounding the intestine. The heavily infected, posterior region of the intestine appeared swollen with the anterior ends of some worms projecting into the peritoneal cavity enclosed in a connective capsule. A cross section of the intestine showed that the intestine was packed with parasites, almost blocking the intestinal lumen Fig’ At the site of parasite attachment, the surface of the intestine appeared Fig… In E. malabaricus the parasites were found to occupy the entire stretch of the intestine posterior to the stomach and the intensity of infection was very heavy. The proboscis of most of the parasites enclosed in a capsule was seen projecting into the peritoneal cavity in a melanised condition, while in L. argentimaculatus it was less.
The several pathological changes and the mechanical damage caused by the Echinorhynchus gadi have totally destroyed the normal ultrastructure of the intestinal tissues. However, the mucosal epithelium, stratum granulosum, lamina propria, muscular and serosa of the wall of the intestine formed a tunnel surrounded with collagenous fibers and granulocytes (Fig. 5a). The intestinal inflammation, granular tissue formation, connective tissue proliferation, associated with the, host immune reactions were evident in the infected tissues. Accumulation of lymphocytes and the presence of large number of granulocytes as well as fibroblasts suggested inflammatory responses (Fig. 5b and c). The lipid droplets seen with in cells in the deeper parts of the parasitic infected host intestine (Fig. 5d). Though the parasite was surrounded in a fibrous capsule of host origin, the integument of the parasite appeared to be unaffected by the inflammatory responses mounted by the host’s immune system (Fig. 5e, f and 6a). The large, last row of spines on the proboscis were seen anchored firmly in the surrounding connective tissue capsule (Fig. 6b). The neck region of the parasite was particularly long, in many cases (Fig. 6c). The proboscis was seen traversing the entire breadth of the intestinal wall reaching the peritoneal cavity, enclosed in a fibrous connective tissue jacket of host origin (Fig. 6d).
Discussion
The pathological consequences of parasite of fishes are well documented and serve as evidence to support the view that parasites are one of the main causes of mortality in fish population. This study was well recorded the pathological changes of marine fishes from Tamil Nadu coast. In case of heavy infections, they can cause occlusion of the gut and invasion or migration of parasites into uncommon locations (Nickol, 2006). The pathological consequences of parasite of fishes are well documented and serve as evidence to support the view that parasites are one of the main causes of mortality in fish population.
The presence of gaps in the infected histological sections of both Yellow perch and Smallmouth bass intestine. These gaps were observed between the proboscis and the host tissue to which it was attached. This apparent retraction of the proboscis from the host tissue has been observed previously (Venard and Warfel, 1953; Bullock, 1963). That is, there would be no gap in an actual infection of L. thecatus in a living Yellow perch or Smallmouth bass because the parasite by definition attached to the intestinal wall with its hooks. But, in the case of the current study so many big size of the gaps observed from the infected intestine pathological sections. In the gaps defense up on the proboscis size hooks and length sine the Acanthocephalan proboscis as well as hooks length is vary from the individuals.
In this study revealed that structural abnormalities such as disruption of infected intestine cells, degeneration, necrosis and also damage of blood vessels in the intestine. The longer praesoma of Acanthocephalan penetrate the deep in the wall and often enter the peritoneal cavity where it is encapsulated by proliferated connective tissue. Akinsanta Bamidele, (2007) reported that the deposition of hemosiderin pigments in both healthy and diseased specimens of catla may probably have some relevance with the poor gonadal maturation of the fish. Haemosiderosis occurs in the form of brown intracellular granules which gives an intensely positive Prussian blue reaction. In the present study, the number of goblet cells was found to be increased in affected region, and increased mucus secretion was observed on the intestine surface. Accumulation of lymphocytes and the presence of large number of granulocytes as well as fibroblasts suggest inflammatory responses.
The extent of inflammation and amount of cellular infiltration associated with L. pagrosomi in the gut of parus major reported by Hatai et al., (1987). The small regions of ecosinophilia beside the parasite wall in both the gut and spleen of yellowfin bream may be associated with cellular necrosis, but an eosinophilic mucus ‘ like substance between the proboscis and bulbous neck region of P.bulbocolli was thought to be secreted by the inner layer of epithelioid fibroblast cells (Chaicharn and Bllock, 1967). In the case of the present study similarly, observed the cell necrosis of the acanthocephala infected tissues. The necrosis due to the hooks and armed of the acanthocephalan.
The differences in the cellular components in inflammation tissue of the stone loach appeared to be correlated with the amount of collagen present (Wanstall et al., 1986). The presence of granulocytes, a few macrophages and a small amount of collagen is used as an indicative of acute inflammation. A chronic inflammatory state is associated with the presence of a large amount of collagen, giant cells and fibroblast (Wanstall et al., 1986). In the present study, also similarly exposed fibroblasts, granulocytes, lymphocytes and macrophages were prominent in the inflammation tissue. Since giant cells were not found in inflammation tissues, it was indicated to acute inflammation. Inflammatory reactions involving cellular responses, either accompanied by the formation of granulomas or not, have been reported for numerous piscine parasites belonging to different groups, such as amoebas, dinoflagellates, diplomonads, kinetoplastids, microsporidians, apicomplexans, ciliates, myxozoans, monogeneans, digeneans, cestodes, nematodes, acanthocephalans and crustaceans (Dykova and Lom, 2007; Alvarez-Pellitero, 2008).
The chronic intestinal damage leads to the inflammatory response and serious illness or high mortality induced by acanthocephalan infected fishes. Pathogenic effects and ultrastructure of acanthocephalans are due to the attachment of the adult parasite in the digestive tract and also in the encapsulation of larval stages in the tissues. The extent of damage is proportional to the depth of penetration of the proboscis (Sanil et al., 2010). There were more significant pathological changes observed in yellowfin tuna as a result of Echinorhynchus gadi infection. Acanthocephalan infections are negligible when parasites are attached to the epithelial mucosa only. Further studies are still required on the other marine fishes of Nagappattinam in order to ascertain the intermediate hosts of these helminthes parasites. Moreover it seems that the Echinorhynchus gadi might be considered as detrimental to fish health. In order to present the intense cases of infestation with parasites, it is important to use a registered efficient safe medicament. However, no reports could be found in the literature on the morphology, histology and ultrastructure of the digestive tract of yellowfin tuna.

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