Pathomorphological and Molecular Studies of Respiratory Mannheimiosis in Goats

Background: Mannheimia is a Gram-negative, facultative anaerobe, non-spore forming and non-motile bacteria belongs to the family Pasteurellaceae. Caprine bacterial pneumonia is most often caused by Mannheimia haemolytica (previously known as Pasteurella haemolytica) and Pasteurella multocida which are more frequently associated with the outbreak of acute pneumonia and death of goats, particularly young once. Mannhemia is an opportunistic pathogen that particularly inhabits the nasopharynx and tonsils of goat and sheep. The present study was aimed to study Mannheimiosis in Guwahati, Assam in order to diagnose and control the disease among goats. Methods: The present investigation was conducted during the year 2021-2022 in Guwahati, Assam. A total of 51 pneumonic lung samples were collected from nearby slaughter houses and during necropsy at Department of Pathology, C.V.Sc., A.A.U., Khanapara, Guwahati-22. All the samples were subjected to primary isolation in blood agar and MacConkey's agar and further confirmation was made using PCR. Result: Out of total 51 pneumonic lung samples examined seven (13.72%) cases were found positive for Mannheimia haemolytica infection where 5 cases were found to be associated with other respiratory pathogens. Visible gross lesions observed during necropsy were broncho-interstitial pneumonia, suppurative pneumonia and fibrinous pneumonia with hemorrhagic tracheitis. Histopathological examination revealed presence of characteristic oat cells, intravascular thrombosis, fibrin balls, oedema, necrosis and polymorphonuclear cell infiltration in the lungs. Bacteriological culture for isolation and identification of Mannheimia haemolytica showed β haemolytic zone on MLA plates. Confirmatory diagnosis was made using PCR targeting 16s rRNA gene with amplicon size 1500 bp and Lkt gene with amplicon size 206 bp. The phylogenetic analysis of 16s rRNA gene from positive sample showed percent identity of above 97% with other strains of Mannheimia haemolytica present in NCBI website. The variability in the lesions observed in the present study it can be concluded that a mixed infection with reduced resistance of the animals contributed to the development of pneumonia rather than Mannheimia haemolytica alone and PCR can be used as reliable technique for confirmatory diagnosis of respiratory mannheimiosis.