Mycobacterium avium subsp. hominissuis infection in horses with granulomatous enterocolitis - first report in Poland

Sep 29, 2026

Uploaded by Muffet

Gastrointestinal mycobacteriosis in horses is challenging to diagnose because Mycobacterium avium subsp. hominissuis is intracellular and clinical signs are non-specific. Current material collection and diagnostic procedures often fail to provide definitive antemortem identification, so culturing, acid-fast staining, histopathology, PCR, and immunological marker assessment were evaluated. Three horses were clinically managed, and an unfavorable course led to euthanasia with necropsy and laboratory investigations. Peritoneal fluid from abdominocentesis supported microbiological and molecular diagnosis in one horse.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages8

Reading Time20 min

AccessFree to download

Abstract

Introduction

Mycobacterial complexes and MAH zoonotic potential

Pathogenesis and survival mechanisms

Material and Methods

Results

Conclusion

Mycobacterium avium subsp. hominissuis infection in horses with granulomatous enterocolitis – first report in Poland Beata Nowicka 1, Wojciech Łopuszyński2􀀍 , Monika Krajewska-Wędzina3, Anna Biazik4, Magdalena Sobuś5, Izabela Polkowska1, Ewelina Szacawa6 1Department of Animal Surgery, 2Department of Pathomorphology and Forensic Veterinary Medicine, 3Department of Food Hygiene of Animal Origin, University of Life Sciences in Lublin, 20-950 Lublin, Poland 4Department of Veterinary Surgery, 5Department of Diagnostics and Clinical Sciences, Institute of Veterinary Medicine, Nicolaus Copernicus University in Toruń, 87-100 Toruń, Poland 6Department of Bacteriology and Bacterial Animal Diseases, National Veterinary Research Institute, 24-100 Puławy, Poland [wojciech.lopuszynski@up.edu.pl](wojciech.lopuszynski@up.edu.pl) Received: May 24, 2025 Accepted: December 2, 2025 Abstract Introduction: Gastrointestinal mycobacteriosis in horses is difficult to diagnose because of the pathogen’s intracellular nature and the non-specific clinical symptoms. Effective accurate diagnosis facilitates prognosis and treatment. Current diagnostic procedures and methods of collecting material do not permit definitive antemortem diagnosis. However, culturing, acid-fast bacilli staining, histopathology, PCR and immunological marker evaluation may prove useful. Material and Methods: Three horses were admitted to a clinic for intensive care and a final diagnosis. Physical examination and additional tests were performed. Unfavourable prognoses and lack of treatment response prompted euthanasia decisions. Necropsy was performed, as were histological, microbiological and molecular investigations. Results: The clinical condition of the animals deteriorated despite therapy. Two horses were euthanised when they did not respond to treatment and had poor prognoses. Intestinal mycobacteriosis caused by Mycobacterium avium subsp. hominissuis was diagnosed postmortem using laboratory investigations. One horse’s diagnosis was established antemortem by cytological and microbiological examination of biopsy material from an abdominocentesis, and this animal was also euthanised because of its poor prognosis. Conclusion: Mycobacteriosis should be considered in the differential diagnosis of chronic debilitating equine diarrhoea in addition to rhodococcosis, lawsoniosis, salmonellosis, gastric ulcers and food intolerance. Peritoneal fluid obtained by abdominocentesis proved to be an effective diagnostic method for microbiological and molecular identification of Mycobacterium avium subsp. hominissuis in horses with suspected enteric mycobacteriosis and concomitant ascites. Keywords: abdominocentesis, enterocolitis, intractable equine diarrhoea, MAH, MALDI-TOF. Introduction Mycobacterial infections in horses are generally rare and require a complex diagnostic approach (4, 5, 9, 15) . Advances in molecular biology, gene sequencing and classification of pathogens have made possible the identification of many species and subspecies within the Mycobacterium genus. Most mycobacteria are grouped into the two most dominant complexes, namely M. tuberculosis complex (MTBC) and M. avium complex (MAC) (18, 36). The first largely comprises the mycobacteria that cause tuberculosis in both humans and animals including horses. Tuberculosis was the world’s second leading cause of death from a single infectious pathogen in humans in 2022 (36) . The second complex, which is responsible for mycobacteriosis, includes two species: M. avium and M. intracellulare, of which the first is split into four subspecies: M. avium subsp. avium, M. avium subsp. silvaticum, M. avium subsp. paratuberculosis and M. avium subsp. hominissuis (MAH). All members have worldwide distribution and zoonotic potential (24, 25). The bacteria of the MAC are widespread in the environment, being found mainly in soil and water reservoirs, both in natural and in tap water. The subspecies other than

FAQs

Why is diagnosing gastrointestinal mycobacteriosis in horses difficult?

Because the pathogen is intracellular and produces non-specific clinical symptoms, existing diagnostic procedures and sample collection may not allow definitive antemortem diagnosis.

How were the three horses diagnosed in this study?

They underwent physical examination and additional tests; necropsy was followed by histological, microbiological, and molecular investigations. One horse also had antemortem diagnosis using cytology and microbiology on biopsy material from abdominocentesis.

What diagnostic role did abdominocentesis/peritoneal fluid play?

Peritoneal fluid obtained by abdominocentesis proved effective for microbiological and molecular identification of Mycobacterium avium subsp. hominissuis in horses with suspected enteric mycobacteriosis and concomitant ascites.

Sep 29, 2026

Uploaded by Muffet