Studies were conducted on the pathology caused due to nemathelminth parasites 55 necropsied sheep. The representative portions of the tissues of abomasum, small intestine, large intestine and lungs harbouring the parasites after collection were examined grossly and histopathologically. Haemonchus contortus infected abomasum revealed traumatic erosions and petechial haemorrhages. Histological examination revealed abomasitis characterized by infiltration of eosinophils, lymphocytes, and macrophages. Colon infected with Chabertia ovina was thickened and edematous. Histologically denudation of mucosa and infiltration of mononuclear cells and submucosal oedema were observed. Oesophagostomum columbianum infected colon revealed nodules throughout the length. Histopathologically diffuse infiltration of lymphocytes, epitheloid cells and macrophages were observed especially surrounding the areas of necrosis. Small intestine infected with Bunostomum trigonocephalum showed thickening of mucosa. Histopathologically diffuse infiltrations of eosinophils were seen in the sections. Caecum infected with Trichuris ovis revealed no changes on gross examination. Histopathological sections revealed mucosal erosions and mononuclear cell infiltration. No gross changes were seen in Nematodirus spp. and Gaigeria pachyscelis infected intestines. Dictyocaulus filaria infectd lungs showed areas of consolidation in diaphragmatic lobes. Copious froth was observed in bronchi and bronchioles along with numerous worms. Histopathologically lung parenchyma revealed congested and haemorrhages. Sections of parasites were seen in the bronchioles and polymorphonuclear cell infiltration was observed in the parenchyma especially near the bronchioles containing parasites.
Sheep rearing is a major source of sustenance for small and marginal farmers and landless labours alongwith conventional agricultural production. Sheep population in India is 62.5 million (F.A.O, 2004) which constitutes 4.6 per cent of world’s total sheep population (17th livestock census, 2003) and ranks 3rd in the world. The sheep population in Jammu and Kashmir is 3.967 million (Statistical Digest, 2007).
Gastrointestinal parasitism has been recognised as a major health issue in small ruminant production systems and its consequences can be extensive ranging from reduced performance to mortality (Sykes, 1994; Waller, 1999). In spite of significant production losses, which may run into millions of rupees (Shah and Chaudhry,1995) the problem is neglected due to its chronic and insidious nature (Sanyal,1998). The productivity of domesticated animals is also adversly affected. The small ruminants are usually parasitized with several species of helminthes which occupy different organ systems of body especially digestive tract and respiratory system. Alimentary tract is comparatively more prone to develop spontaneous pathological conditions due to parasitic infection than any other single organ/ system in the body. Therefore the present paper deals with the pathological changes caused by nemathelminth parasites in sheep.
Materials and Methods
The study was carried out in locally reared sheep from September 1st 2008 ro August 31st 2009 in Ganderbal district of Kashmir valley. The abomasum, parts of small intestine, large intestine and lungs of 55 locally reared sheep and cases brought for postmortem examination were examined for macroscopic lesions and the gross lesions observed were noted down. Only representative cases were studied which harboured single species of parasites. For histopathological studies fresh tissue pieces showing gross lesions were fixed in 10% formalin and preserved. The slides were prepared using conventional technique ans stained with Haematoxylin and Eosin stains for histological examination.
Results and Discussions
Out of 55 cases examined, 40(72.72%) were found positive. Haemonchus contortus was found to be most prevalent (50.90%), followed by Trichuris ovis (30.90%), Chabertia ovina (20.00%), Dictyocaulus filaria (16.36%), Oesophagostomum columbianum (12.72%), Bunostomum trigonocephalum (7.27%), Trichostrongylus spp. (3.63%), Nematodirus spp. (1.81%) and Gaigeria pachyscelis (1.81%).
In case of Haemonchus contortus, abomasum had thickened walls and oedematous folds. The mucosa was swollen and covered with small red bite marks of the parasites. Some cases revealed haemorrhagic points on the mucosal surface. Histologically dilated and engorged blood vessels alongwith mononuclear cell infiltration in the mocosa sometimes extending to the submucosa was seen. Erosions were seen on the mucosal surface. These changes resembled to the findings of Al-zubaidy et al (1987), Mallick et al (1978), Rahman and Collins (1991). Abomasitis, characterized by infiltration of eosinophils, lymphocytes and macrophages along with increased number of mast cells which were evident in the lamina propria and mucosa of the abomasum. (Fig1). Similar changes were reported by Darzi et al (2004) on necropsy and histological examination of abomasum of corriedale sheep infected with Haemonchus contortus. The prominent eosinophillic response noted in parasitized abomasa was attributed to tissue invasive phase of the infection. The traumatic erosions on the mucosal surface may be due to an active feeding habit of developing stages of the parasites. No gross changes were observed in case of Ostertagia and Trichostrongylus infected abomasum.
Gross examination of small intestine infected with Bunostomum trigonocephalum revealed oedema. Histopathologically the main lesion associated with Bunocephalum trigonocephalum were abrasion of villi and hyperplasia of the crypts of liberkuhn (Fig 2).
These histological changes were found in the proximal small intestines which correspond to the site of prediliction for most species. These histological lesions develop rapidly after with signs of degeneration and severe alteration in brush border. Hyperplasias of villi and crypts have been described as adaptive response of the organ to the nematode infection.
Colon infected with Chabertia ovina revealed oedema and thickening of mucosa with inflammation, patchy congestion and some haemorrhages. The affected area was congested, swollen and covered with mucous in severe cases. Histopathologically the adjoining parts of the mucosa showed increased activity of goblet cells and infiltration with lymphocytes and eosinophils. Denudation of mucosa, sub mucosal edema and infiltration of lymphocytes and globular leukocytes were also seen (Fig 3). Solusby (1982) also reported that adult worms of Chabertia cause the mucosa to become thickened and edematous. The infiltration of cells may be due to the response of tissue to the invading phase of the parasite.
In case of Oesophagostomum columbianum the gross examination of large intestine especially caecum and colon revealed the presence of white thread like worms in the lumen. Small nodules of varying sizes were found on the serosa of large intestine which on incision revealed creamy and caseated exudates. Besides this, there was thickening of intestinal mucosa. Histopathologically there was hyperplasia of goblet cells and infiltration of lymphocytes in the mucosa. Nodular areas of caseous necrosis with calcification were present deep in the mucosa. Also epitheloid cells and macrophages were observed especially surrounding the areas of necrosis (Fig 4). These granulomatous nodular lesions in the parasitized intestine werer similar to those described by Jubb et al (1993). Shelton and Grifth (1969) and Alok et al (1997) also observed thickening of mucosa, nodule and creamy exudates material.
In case of Trichuris ovis infection anterior end of the worm was embedded in superficial epithelium with their posterior end free in the intestinal contents. No gross changes were seen. Histopathologically mucosal erosions were seen accompanied with sparse infiltration of mononuclear cells (Fig 5). Similar types of changes were reported by Alok et al (1997). Sparse infiltration of mononuclear cells may be due to response of tissue to the invading parasite. No changes were observed in Nematodirus, Gaigeria infected small intestine.
Numerous Dictyocaulus filaria were recovered from the lungs admixed in a much copious froth throughout the bronchial airways. Scattered throughtout the lung surfaces were noted slightly sunken, dark consolidated areas among normal ones. In severely affected cases lumps of worms appeared to obliterate secondary bronchioles. Histopathological sections revealed congestion and haemorrhages in lung parenchyma. Sections of parasites were seen in the bronchioles. Numerous macrophages were present in the alveoli. Polymorphonuclear cell infiltration was observed in the parenchyma especially near the bronchioles containing parasites (Fig 6). Similar findings were reported by Nashiruddullah et al (2007).
The authors are highly thankful to Division of veterinary Pathology for providing necessary laboratory facilities in order to carry out the research programme in their laboratory.
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