Viral encephalitis has caused at least 56 deaths in India's western state of Gujarat, forcing authorities to step up surveillance for the disease caused by a viral infection often spread by sand flies and ticks.

Viral encephalitis, which can cause high fever and in many cases affect the brain, is common in several parts of India during the monsoon season, but many of the deaths in Gujarat were caused by the Chandipura virus, a relatively new form that is known to affect mostly children under 15.

Of the 56 dead over the last month, a quarter were confirmed to have died from the Chandipura virus, Gujarat Health Commissioner Harshad Patel said.

"Almost all the patients are children. As far as I know, this virus affects only children," Patel told Reuters about the outbreak.

Patel said that local health authorities have been monitoring encephalitis cases for a month and would continue to keep a close eye on infections in the general population, stepping up surveillance in areas which have reported cases.

A total of 133 cases of viral encephalitis , including 47 cases caused by the Chandipura virus, have been registered in the state of 70 million people in a month, the state government said in a statement.

The Chandipura virus, named after a small town in the western state of Maharashtra where it was first discovered, is known to cause sporadic cases of encephalitis and there have been outbreaks in the western, central and southern parts of the country, a health ministry statement said last week.

"It is transmitted by vectors such as sand flies and ticks. It is to be noted that vector control, hygiene, and awareness are the only measures available against the disease," the statement said.

Cases of viral encephalitis first came to light in two northern districts of Gujarat last month. However, more cases have since been registered from across more than two dozen districts, according to government data.