Fatal equine gas gangrene associated with Clostridium septicum in the Brazilian Amazon: clinicopathological and molecular characterization of a 20-case series.

Fatal gas gangrene caused by Clostridium septicum was studied in 20 horses from the Brazilian Amazon, detailing clinical signs, pathological findings, and molecular diagnosis. All cases resulted in death despite treatment, highlighting the disease’s rapid progression and the need for early diagnosis and careful clinical practices.

Introduction and Background

• Equine gas gangrene is a severe and rapidly progressing muscle infection characterized by necrosis and systemic toxicity.
• It typically features sudden onset of lameness, swelling, and gas accumulation in muscles.
• Clostridium septicum is one of several clostridial bacteria known to cause histotoxic infections, but cases from tropical regions like the Amazon are underreported.
• This study fills a gap by documenting a comprehensive case series in a tropical setting.

Study Design and Case Description

• The study analyzed 20 fatal cases of equine gas gangrene diagnosed between 2018 and 2026 in Pará State, Brazil.
• All affected horses showed sudden severe limb lameness and swelling, often with subcutaneous crepitus, indicating gas presence under the skin.
• Most cases followed a breach of tissue integrity such as puncture wounds, trauma, or intramuscular injections, which likely predisposed horses to infection.
• Despite receiving antimicrobial and anti-inflammatory treatment, the horses rapidly deteriorated and died or were euthanized due to poor prognosis.

Pathological Findings

• Necropsy revealed widespread muscle destruction characterized by hemorrhagic myonecrosis and serosanguineous fluid.
• Accumulation of gas was evident within muscle and subcutaneous tissues, a hallmark of clostridial infections.
• Histological examination showed extensive coagulative to floccular necrosis of muscle fibers, marked tissue edema, and hemorrhage around vessels.
• Frequent thrombosis within blood vessels was noted, indicating vascular injury.
• Large numbers of bacillary (rod-shaped) bacterial structures consistent with clostridia were observed within the lesions.

Molecular Diagnosis

• Targeted multiplex PCR was used to detect DNA of major histotoxic clostridial species in affected muscle tissue samples.
• Clostridium septicum DNA was identified in all 20 cases, confirming this species as the etiologic agent.
• No DNA from other clostridial species was amplified, reinforcing the specific association with C. septicum.

Clinical and Epidemiological Implications

• The study underscores that C. septicum can cause fatal gas gangrene in horses living in tropical environments.
• Rapid clinical progression and high fatality emphasize the need for early detection and aggressive intervention.
• Prevention should focus on strict aseptic techniques during procedures that break the skin, such as intramuscular injections, to reduce infection risk.
• Integration of pathological examination with molecular techniques is essential to confirm diagnosis and guide treatment decisions.

Conclusion

• This case series provides critical, systematically documented evidence from a tropical region, expanding understanding of clostridial gas gangrene in horses.
• The findings highlight the importance of clinician awareness, meticulous clinical hygiene, and the use of modern molecular diagnostics in managing this rapidly fatal disease.