* Skin: This is the most obvious and characteristic symptom. The virus causes a rash that progresses through stages: macules (flat red spots), papules (raised bumps), vesicles (fluid-filled blisters), pustules (pus-filled blisters), and scabs.

* Lymphatic System: The virus multiplies in lymph nodes, leading to swelling and pain.

* Immune System: The body's immune response to smallpox is often severe and can contribute to complications.

* Respiratory System: Smallpox can cause pneumonia, which can be fatal.

* Gastrointestinal System: Smallpox can cause nausea, vomiting, and diarrhea.

It's important to note that smallpox is a highly contagious and potentially fatal disease. However, thanks to successful vaccination efforts, it has been eradicated globally.