Red Leg is a short-term infection, capable of infecting amphibians. The infection leads to the diseased frog's leg turning a bright reddish color, eventually leading up to the entire body, killing the frog.
Its symptoms are easily mistaken with the effects of a type of fungi that Anne prepared for the Plantar family in a soup. These effects, similar to Red Leg, caused the family to turn bright red, starting from the bottom.