Was trench foot a new disease in World War 1?

No, it was not a new disease.

Trench foot is a medical condition that affects the feet and can occur in times of prolonged wet and cold weather, such as in trench warfare. The condition was previously referred to as "immersion foot" and was known as early as the American Civil War. In World War 1, the incidence of trench foot greatly increased due to the extensive periods of fighting in wet and muddy trenches, affecting numerous soldiers.