The comparative pathology of equine cutaneous phycomycosis.

This research conducts an in-depth pathological comparison of three types of fungal infections – pythiosis, basidiobolomycosis, and conidiobolomycosis – in horses, detailing the distinct characteristics of each and their associated symptoms.

Research Overview

• The research focuses on a comparative study of three types of phycomycosis (fungal infections) in horses, specifically pythiosis, basidiobolomycosis, and conidiobolomycosis.
• These diagnoses were made based on morphological analysis from a sample of 266 horses with phycomycosis.

Findings

• All diagnosed cases presented with ulcerative granulomas on the skin. Three horses with pythiosis also had metastatic lesions in regional lymph nodes.
• Pythiosis lesions showcased yellow, coral-like coagula with a fibrotic surface containing sinus tract openings.
• Basidiobolomycosis was identified by infrequent small yellow coagula and a struck yellow line of fungal invasion beneath a swollen surface.
• Conidiobolomycosis had numerous small coagula and generally affected the nasal region of the horses.
• Some differences were noted in the inflammatory cell populations within the granulomas but were mostly attributed to the coagula size and fungal morphology.

Composition of Coagula

• Coagula, observed in different forms across the three diseases, consisted of collagen, fibrin, cellular debris, degranulated and whole eosinophils, and hyphae (a part of the fungal cell).

Histochemistry Analysis

• No significant differences were found among the three diseases when evaluated using histochemistry, a technique that uses staining methods to highlight cellular components.

Fungal Characteristics

• Pythium sp hyphae measured between 2.6 and 6.4 micrometers in diameter, had thick walls, and sometimes featured partitions (septa).
• Basidiobolus haptosporus hyphae ranged from 5.1 to 20.5 micrometers in diameter, possessed thin walls, and commonly had septa.
• Conidiobolus coronatus hyphae measured between 5.1 and 12.8 micrometers in diameter, had thin walls, and also generally featured septa.

Additional Observations

• The latter two fungi were associated with a perihyphal eosinophilic cuff (also known as the Splendore-Hoeppli phenomenon) with a radius of up to 20 micrometers.
• Upon analyzing the ultrastructure of the fungi, it was found that P. sp had a thick, singular density cell wall, while B. haptosporus and C. coronatus had thin, double-layered cell walls.