Fruit bats were the source of Nipah virus which created havoc in Kerala's Kozhikode in May according to the Indian Council of Medical Research (ICMR), an official said on Tuesday.

Kerala Health Secretary Rajiv Sadanandan said that tests of the first batch of 21 bats were were negative, but the second set of tests done on 55 fruit bats from Kozhikode confirmed that the nocturnal mammals were behind the spread.

Sadanandan told IANS that Union Health Minister J.P. Nadda on Tuesday confirmed the latest test results.

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At least 13 people died and more than 2,000 were kept under observation when the virus struck in May. Most of them were from Kozhikode district and some from Malappuram.

Even when the final green signal came from Kerala health authorities that the fear of the spread has been contained, the source of the virus outbreak was yet to be ascertained.

The ICMR is the country's premier body engaged in formulation, coordination and promotion of biomedical research. (IANS)