Mycobacterium branderi Infection in a Horse with Granulomatous Mesenteric Lymphadenitis.

The research paper documents the occurrence of an infection caused by Mycobacterium branderi in a horse, represented as the first known case of this bacteria affecting a horse and resulting in granulomatous mesenteric lymphadenitis.

Overview of the Case

• The research starts off by discussing a unique case of a 17-year-old Thoroughbred stallion suffering from chronic diarrhea, cachexia, and ventral and cervical edema for 3 months.
• The post-mortem inspection revealed severe proliferation of mesenteric lymph nodes, abnormal dilation of lymph vessels (lymphangiectasia), and noticeable thickening of the small intestinal mucosal lining.

Microscopic Examination

• The microscopic examination of the mesenteric lymph node showed widespread granulomatous, or nodular, inflammation. This essentially replaced the majority of the nodal tissue. Acid-fast bacilli, a type of bacteria, were found within the cytoplasm of the macrophages, a kind of immune system cell.
• Furthermore, it was revealed that there was wide diffusion of lymphangiectasia, a disease condition where the lymph vessels are dilated.

Bacteriological Findings

• Although fresh samples of the mesenteric lymph nodes didn’t result in bacterial growth, the usage of the nested polymerase chain reaction (PCR), a highly sensitive technique to amplify DNA, indicated the presence of M. branderi, a non-tuberculous bacterium. This is noteworthy as this is the first reported instance of such an infection occurring in horses.
• Generally, M. branderi is known to cause respiratory infections in humans; however, this report suggests it can also have a significant impact on the gastrointestinal health of horses.

Importance of the Findings

• The researchers present the case as a necessary addition to the veterinary differential diagnosis repertoire, emphasizing that M. branderi infection should be considered in chronic diarrhea cases in horses. This is especially so if such cases are accompanied by granulomatous enteritis and lymphadenitis, symptomatic conditions characterized by inflammations of the intestine and lymph nodes respectively.