In a study carried out on spontaneous lung lesions in slaughtered sheep, pleuritis was observed in 6 (3.21%) cases out of 187 lung samples examined by gross and histopathological examination. Gross examination revealed thickened pleura with glistening surface. Microscopically, the pleura were edematous and revealed increased proliferation of fibrous connective tissue with infiltration of lymphocytes.
Pleuritis is an inflammation of the membrane that surrounds and protects the lungs resulting in fibrous adhesions between lung and chest wall. Inflammation occurs when an infection or damaging agent irritates the pleural surface and causes substantial economic losses to the farmers. These losses are associated with downgraded or condemnation of carcasses (Azizi et al., 2013). This pleuritis is caused by one or more number of bacteria (Manheimia and Mycoplasma) and viruses. These bacteria were present in sheep lungs as commensals and only cause disease under certain circumstances like stress and dusty conditions (Robert Suter, 2016). Pleuritis lesions never resolve completely and permanent fibrous scars remain on lungs and parietal pleura these lesions persist after pneumonia resolves and appear to accumulate with successive episodes of pneumonia (Davies, 1985 and Pfeffer, 1986). The present paper describes the gross and histopathological changes observed in pleuritis in sheep.
Materials and Methods
A total of six pleuritis cases from slaughter house located in Gannavaram were included in the present study. For histopathological examination, representative samples were fixed in 10% neutral buffered formalin. Fixed tissues were routinely processed to obtain 4 – 5µ thick paraffin sections and staining as per standard procedures. Haematoxylin and Eosin and Masson’s trichrome stained sections were examined microscopically.
Results and Discussion
Pleuritis was observed in six (3.21%) cases out of 187 sheep lungs examined. Grossly, thickened pleura with glistening surface was seen which was hard to cut (Fig.1). Microscopically, the pleura were edematous and revealed increased proliferation of fibrous connective tissue with infiltration of lymphocytes (Fig. 2). The fibrous connective tissue takes blue colour with Masson’s trichrome stain (Fig. 3).
Fig.1: Pleuritis- Cut Surface of the Lung Revealed Thickening of Pleura with Glistening Surface
In the present study, 6 (3.21%) cases manifested pleuritis which was higher when compared with the reports of Chattopadhyay et al.,1986 and Azizi et al., 2013 they reported 3 (0.44%) out of 675 lungs and one case (2.38%) out of 42 lungs respectively. In this study, the affected areas revealed excessive pleural thickening with glistening surface grossly and edema, infiltration with numerous lymphocytes and proliferation of fibrous connective tissue microscopically. The gross and histological picture in the present study was in agreement with the findings of Davies (1985), Pfeffer (1986), Dar et al., 2012.
Fig. 2: Lung Pleuritis – Section showing Fibrous Connective Tissue Proliferation and Infiltration of Mononuclear Cells H&E X 40
Fig. 3: Lung Pleuritis – Section showing Fibrous Connective Tissue Proliferation (blue colour), Masson’s Trichrome x 40
Usually, pleuritis may be due to trauma, stressors, dusty conditions and infectious agents as that of pneumonia, but most possibly it is of bacterial cause, through hematogenous route or blood borne seeding (McGavin and Zachary, 2007). To reduce the incidence of pleuritis remove the stressors and infectious agents that predispose sheep to the condition.
In the present study, carried out on spontaneous lung lesions in slaughtered sheep, pleuritis was observed in 3.21% cases out of the total samples and they revealed thickened pleura with glistening surface on gross examination. Microscopically, the edematous pleura with lymphocyte infiltration were observed.