April 7 is World Health Day. The theme this year is 'Vector-borne diseases - small bite big threat' and one of the most common vector-borne diseases is dengue fever. The incidence of dengue has risen significantly in the past few decades. According to the World Health Organisation (WHO) more than 2.5 billion people in the world are now at risk of suffering from dengue. Dengue is a mosquito borne viral infection. In simple words dengue is caused by dengue virus that gains entry into the human body via mosquito bites. Because dengue is a viral disease there is no definitive