It's believed one's body would be overheated when one is down with dengue and that also caused the patient to have fever. Papaya juice has cooling effect. Thus, it helps to reduce the heatiness in one's body, thus the fever will go away. I found that it's also good when one is having sore throat or suffering from heatiness.
I've always been interested in traditional Indian medicine's idea that some things are heating, and some cooling, and that an imbalance between the two causes illness. For instance, mangoes are hot. If you gorge on mangoes and get diarrhoea, it is because you have overheated your system. Some foods are obvious: chillies, onions, garlic are hot, yoghurt is cooling. Others, like the mangoes, are not so obvious, at least to me.
I never knew what to call the condition of heat overload, and now I do: 'heatiness.' I think this is a great word, with many applications. In this fast-paced world of ours, there is altogether too much heatiness; and papaya leaf juice, yoghurt or any other cooling substance is certainly worth trying, to get the temperature down.