Malignant catarrhal fever in swamp buffaloes (Bubalus bubalis): A retrospective pathological study of outbreaks in Thailand

Malignant catarrhal fever (MCF) is a highly fatal disease of ruminants which has not been extensively studied in Thailand. The aim of this study was to describe the clinical signs and pathological findings of MCF-affected buffaloes (n=13), in the Nakhonpathom province of Thailand. All cases were collected between May 1996 and August 2000. Before the 1998 outbreak, four clinically normal sheep were moved into a pen adjacent to the buffaloes pens. The animals developed clinical signs of severe depression, anorexia, high fever, hypersalivation, and corneal opacity-associated excessive lacrimation. Necropsy revealed severe haemorrhages in various organs including the oropharynx, trachea, heart, kidneys and urinary bladder. Ulcerative stomatitis and abomasitis was often present. Diphtheritic tracheitis and/or pharyngitis were seen in 7/9 (77.8 percent) cases. Histopathologically, generalised vasculitis with occasional fibrinoid degeneration was a pathognomonic lesion detected in all cases in this study. Lymphoid infiltration was recognized in various organs, including the liver, eyes, and meninges, tracheal and intestinal submucosa. In this study, interstitial nephritis and non-suppurative myocarditis were markedly noticed. A skin lesion, consisting of chronic vasculitis, was observed in one buffalo, and is an unusual feature of MCF. The diagnoses of MCF in this study were based on histopathology and a nested polymerase chain reaction (PCR) result in one case. In conclusion, MCF was a highly fatal disease of buffaloes, and generalised vasculitis was clearly detectable in all cases. It is possible to speculate from the history of the outbreak, that MCF in buffaloes, in this study, was associated with sheep.