AVIS - Foot and Mouth Disease - Clinical Disease and Diagnosis

Ageing Of Lesions

Characteristics

The main stages in the progression of vesicular lesions on the tongue of cattle and the feet of pigs over time are as follows:

Characteristics

Approximate Age

Unruptured vesicles, some fluid present, early signs of necrosis in overlying epithelium

1 day

Unruptured, fluid-filled vesicles, overlying epithelium necrotic

1-2 days

Vesicles ruptured, erosions present with ragged portions of epithelium adherent to the margins of the lesions

1-3 days

Erosions with little epithelium attached, margins of lesions losing 3 but sharpness due to early healing

<7-10 days

Healing advanced with marked fibrous tissue in-filling

7-10 days

The ageing of lesions older than one week can best be done in pigs by studying their foot lesions. If a lesion is still at the coronary band it is unlikely to be more than one week old. After this the break in the continuity of the horn gradually grows down the claw at a rate of around 1 mm per week. Therefore, by allowing one week for the lesion to grow out of the coronary band and by adding one week for each millimetre that the lesion in the horn is distant from the coronary band, a rough estimate can be made of the age of a lesion.