With the arrival of monsoon there comes viral fever also. Generally, viral infection increases due to scorching heat in the day and cold weather during night. People having low resistance power become prey to viral infection.  In changing season, viruses are usually more active.
Causes
Most viral infections are spread by the intake of contaminated water or food, or by direct contact. The infection then spreads locally and, thereafter, enters into the blood stream or lymph channels.
Some of the other factors which cause viral disease include fatigue and overwork, emotional stress, poor nutrition, smoking, living or working in crowded conditions.
Prevention 
"One should avoid drinking chilled water, too much of ice creams and other cold things in the changing season. Avoid fermented food like curd, pickles, etc. Also, avoid too much of fasting, as it can lead to acidity and gastro problems. It is advisable to drink plenty of water and boiled water is recommended. One must eat good quantity of green leafy vegetables, roughage to avoid constipation and get adequate vitamins. Develop habit to consume small quantity of food on shorter intervals so that there is enough time for digestion. Do not let rain water stagnate, especially around residential areas. Besides, some natural herbs that can be very useful are saunth, belgiri churan, moong dal, neem leaves, giloye, guruch, etc," says
Dr Verinder Anand, consultant, Internal Medicine, Moolchand Medcity.
—Vani Vyas