Is pruritus (body) a common allergy symptom? Are allergy induced pruritus alleviated with anti histamines? How different from miliara rubra?

Yes. Allergy is usually associated with itching at the affected organ but most itching are not caused by allergies. Dry skin is by far the most common cause for itching without a skin rash. If the itching is caused by allergies (but not contact allergy), antihistamine in sufficient doses would work. In contact allergy involving the skin, topical cortisone works far better.