Cutaneous nodular phaeohyphomycosis in five horses associated with Alternaria alternata infection.

The research article discusses a study on nodular skin disease, a common condition in horses, which in five particular cases was associated with fungal infection caused by Alternaria alternata. The horses presented with facial nodules with features characteristic of lymphoid follicle formation.

Detailed Explanation of the Study

The research studies five horses, all five years of age or less, that were diagnosed with single or multiple facial nodules. Importantly, the lesions associated with this condition have not been associated with a fungal infection in horses previously.

• The horses did not present symptoms like pain or itching, making the nodules asymptomatic.
• Biopsies of the lesions were done for further investigation of the disease.
• The biopsy samples were placed in 10 per cent buffered formol saline for preservation.

Findings from the Histological Analysis

Histological sections of the skin lesions were stained with haematoxylin and eosin, providing details about the structure and composition of the nodules.

• The analysis revealed an unencapsulated but well-circumscribed mass in the mid to deep dermis, separating and distorting adnexal structures.
• The lesions primarily consisted of small, mature lymphocytes, with plasma cells, histiocytes and neutrophils present in smaller numbers.
• Lymphoid follicles with germinal centres were prominent in all cases except for smaller, early-stage lesions.
• A minor characteristic observed was small clusters of neutrophils surrounded by macrophages, forming indistinct pyogranulomas.
• Significantly, fungal elements were detected using the Periodic acid-Schiff reaction (PAS) stain, indicating the presence of a fungal infection caused by Alternaria alternata.

Observations from Individual Cases

Individual observations were made for each horse, contributing to the understanding of the disease’s progression and treatment.

• Horse 1 developed multiple nodules over a 2-year period and underwent several biopsies. The inflammatory reaction and the nature of lesions varied depending upon the stage of lesion development. Despite surgical removal of most of the nodules, new lesions appeared approximately 12 months later.
• The mare (Horse 1) was treated with sodium iodide and no more nodules were observed for several months afterwards.
• Horse 2, who presented with two nodules, exhibited spontaneous reduction of the nodule size without treatment.
• For horse 3, the excision of the original lesion appeared to be curative, with no further lesions developing.

The findings of this research suggest that a fungal infection, not previously associated with equine nodular skin lesions, can be a possible cause of this condition. It also highlights the variable response of the horses to different types of treatment.