Generalized Equine Cutaneous Mastocytosis.

This study investigates a case of generalized cutaneous mastocytosis in a newborn foal, its progression, and its characteristics, including the presence of an equine herpesvirus, in which no direct link with the disease was established.

Overview and Progression of the Disease

• The research begins by precisely depicting a newborn equine case of generalized cutaneous mastocytosis. This is an unusual condition wherein the skin is infiltrated with mast cells, leading to various skin abnormalities.
• The first signs in the foal were numerous small clusters of mast cells on the skin. These progressively grew, became ulcerated, and then naturally disappeared.
• While new lesions continued to appear during the first month of life, they finally started to decline in number.

Characteristics of Advanced Lesions

• Advanced stages of the lesions were recognizable through eosinophil infiltration, collagen necrosis, and fibroplasia.
• Mast cells were abundantly found in biopsies of lymph nodes, spleen, and bone marrow of the sick foal.
• The death of the foal revealed discrete clusters of mast cells in the bone marrow, however, no other notable changes were observed.

Mast Cells Features

• Mast cells were found to be rich in histamine, but comparatively poor in serotonin. This differential chemical composition affects the pathways by which mast cells contribute to immune responses.
• Their cytoplasmic granules mainly appeared granular with only a few showing denseness under the microscope.

Cell Culture Observations

• In cell culture experiments, it was observed that mast cells from early lesions kept dividing till 14 passages while those from older lesions were quickly overgrown by fibroblasts. This suggests that the disease state affected the life cycle and proliferation tendencies of mast cells in the afflicted animal.

Presence of Equine Herpesvirus

• An equine herpesvirus was isolated from the cultures of both the mast cell lesions on the skin and spleen. However, the researchers did not establish a direct connection between this virus and the disease.