Diagnosis was based on postmortem examination of gross lesions, followed by histopathology and tissue smear examination. The animals presented for necropsy were highly emaciated. Three pigs (7.14%) were diagnosed positive for tuberculosis. All the positive cases were of generalized tuberculosis as there were lesions is spleen as per
Radostits et al., (2006). Eight pigs (19.04%) had nodules in either lungs or liver but these were diagnosed negative for TB on ZN staining. This can be attributed to the regressive nature of the disease in pigs often negative on culture and guinea pig inoculation
Radostits et al., (2006). Our results are in collaboration with earlier studies on prevalence by
Palanivel et al., (2011) and
Arega et al., (2013). Lower prevalence is also stated by
Radostits et al., (2006) but they are of view that the lower prevalence reflects the prevalence in the local cattle population from which the infection derives either by ingestion of dairy products or by grazing on same pasture as cattle or bedded on shavings already infected with
M. bovis. The lower relative prevalence in pigs might be due to a number of factors particularly the tendency of the disease to remain localized and early age of slaughter.
In infected pigs, typical tubercle lesions were evident in liver, spleen and lungs and were characterized by the presence of circumscribed yellowish white raised lesions of various sizes and numbers (Fig A, B, C, D). Spleen surface was dry, shriveled with blackish discoloration (Fig C). The affected lungs of different pigs also showed chronic pneumonic lesions (Fig D). Kidneys were smaller in size than normal. Large encapsulated nodules containing yellowish white exudates were observed in some of the affected organs. After cutting tubercle a gritty sensation could be felt indicating that majority of the lesions collected were calcified. The present gross pathological findings corroborated with the earlier findings of
Bolin et al., (1997), Pavlik et al., (2005), Palanivel et al., (2011) and
Arega et al., (2013). Typical tubercle lesions were not found in any of the lymphnodes even in cervical lymph nodes also which were contrast with findings of
Palanivel et al., (2011) and
Arega et al., (2013). Radostits et al., (2006) has also suggested localization as non-progressive abscess in the lymphnode of head and neck as the most common findings although generalized tuberculosis as seen in our study, is not uncommon.
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Histopathologically, granulomatuous lesions characterized by necrotic areas surrounded by mixed inflammatory cells and occasionally by multinucleated giant cells were found in the liver (Fig 1). Caseous necrotic areas surrounded by macrophages, lymphocytes, plasma cells and peripheral fibrosis were detected in the lungs and spleen (Fig 2 and 3). Often there was a surrounding of moderate layer of epithelioid cells, multinucleated giant cells, collar of lymphocytes and plasma cells in liver, lungs and spleen (Fig 1, 2 and 3). The microscopic lesions observed was in agreement with the earlier findings of
Bolin et al., (1997), Koni et al., (2016) and
Singh et al., (2017). No acid fast bacilli or any other bacteria or fungi were seen in the tissue sections. The ZN stain reveals presence of acid fast bacilli as red rods in impression smear made from lung, spleen and liver (Fig 4) which was similar with the findings of
Bolin et al., (1997), Pavlik et al., (2005), Palanivel et al., (2011), Koni et al., (2016) and
Singh et al., (2017).
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The most important observation in this study was prevalence of tuberculosis in pigs to a considerable extent in the form of generalized infection in Ayodhya and Sultanpur district which comes under Middle Gangetic Plain of Eastern Uttar Pradesh. The source of infection for swine might be sawdust, wood shavings, peat, soil, kaolin, water or feces of infected poultry, wild birds and swine or uncooked garbage. Therefore, this study recommends screening of pigs to assess the carrier status so that effective control measure can be made to stop the incidence of tuberculosis in other animals and swine unit workers keeping in view of zoonotic importance of
Mycobacterium spp. The occurrence of tuberculosis is linked to both management and ecological factors. Thus, particular attention is needed in the farm having different species of domestic animals. There is an urgent need to develop technique that not only identify and characterize tubercle bacilli but also facilitate epidemiological studies in order to back trace of infection thereby facilitating formulation of effective control strategies for both animals as well as humans.
