"Either that or dengue fever, she's not sure. Mark diagnosed her with beriberi."

Dengue fever is a virus spread by mosquitoes. Symptoms include extremely high fever, rash, aches, nausea and fatigue, which can persist for a week or more. However, dengue fever is not life-threatening, and patients will recover without treatment. Dengue fever is found in South and Central America, sub-Saharan Africa and South East Asia; it is not usually found in English school girls.

Beriberi is caused by a lack of vitamin B1 (thiamine) in the body. It leads to tingling or loss of feeling in arms and legs, paralysis of the legs, mental confusion, pain and vomiting. Today, except in people genetically unable to absorb vitamin B1, the general improvement in nutrition around the world has made beriberi extremely rare. It is now most commonly found in alcoholics, as alcoholism is associated with poor nutrition and also reduces the body's ability to absorb vitamin B1.