First confirmed case of equine pythiosis in Northern Veracruz, Mexico.

Overview

• This research documents the first molecularly confirmed case of equine pythiosis in Northern Veracruz, Mexico.
• An adult horse exhibited severe skin disease caused by Pythium insidiosum, confirmed through histopathology and PCR testing.

Introduction to the Case

• The subject was an adult horse presenting with a tumor-like skin condition on its shoulder.
• Clinical signs included:
  • Ulcerative and proliferative skin lesions.
  • Pyogranulomatous inflammation characterized by pus and granuloma formation.
  • A crater-shaped mass with serosanguinous (blood-tinged serum) discharge.
  • Fistulas (abnormal openings) that emitted caseous (cheese-like) material.
• Based on these symptoms, a diagnosis was pursued to identify the causative agent.

Diagnostic Procedures

• The tumor was surgically removed and subjected to laboratory examination.
• Histopathological examination involved:
  • Staining with Grocott-Gomori methenamine silver, a technique effective in detecting fungal and fungal-like organisms.
  • Observing necrotic material, fibrosis, and infiltrating immune cells.
  • Identifying brown-colored hyphae, which are filamentous structures typical of Pythium species.
• Molecular identification was performed through:
  • Conventional Polymerase Chain Reaction (PCR) targeting the internal transcribed spacer 1 (ITS-1) region of the pathogen’s DNA.
  • This genetic marker helps differentiate Pythium insidiosum from other organisms.
  • Sequence comparison revealed close relation to strains previously identified in the US and Central America.

Significance of Findings

• This case is the first confirmed report of equine pythiosis caused by Pythium insidiosum in Mexico, expanding the known geographical distribution of this pathogen.
• Equine pythiosis is a serious disease often difficult to diagnose due to its resemblance to other granulomatous skin infections.
• Early and accurate diagnosis is critical for effective treatment, generally involving surgical excision combined with other therapies.
• This report highlights the importance of molecular methods like PCR in confirming infections by oomycetes like Pythium, which are often mistaken for fungi.

Context on Equine Pythiosis

• Pythium insidiosum is an aquatic oomycete pathogen causing invasive tissue infections mainly in horses and other animals.
• The disease manifests typically in tropical and subtropical environments where the pathogen thrives in standing water and moist soil.
• Clinically, lesions are chronic, with discharging masses that can severely compromise animal health if untreated.
• Geographic confirmation of cases informs veterinarians about emerging risks and guides surveillance efforts.