Final answer:
A late sign of disease is a symptom that appears as the condition progresses, and for herpetic gingivostomatitis caused by HSV-1, the late sign of cold sores can initially be seen on the lips and mucous membranes.
Step-by-step explanation:
A late sign of disease is an indicator that appears as the disease progresses and is typically more specific to the disease than earlier signs. These signs are often manifested in distinct areas of the body and can be more severe. An example of a late sign can be seen in the description of herpetic gingivostomatitis, where infection by HSV-1 commonly manifests as cold sores or fever blisters, usually on or around the lips.
This symptom is a late sign that can first be seen on the lips and mucous membranes. Other diseases also show distinct late signs, such as Koplik's spots on the oral mucosa in measles or dark lesions on the mucous membranes in cases of skin cancer.