The Nipah virus is back in the news. For the fourth time in five years, Kerala is battling an outbreak of Nipah. The virus, first documented in Malaysia in 1998, is zoonotic, which means it is transmitted to people from animals, in this case the animals are believed to be the fruit bats of the Pteropus species. As of September 15, six people have tested positive for Nipah virus, and two have died. A Central government team is in Kerala at present and a mobile testing lab has been set up. In infected people, the World Health Organisation says, the virus can cause a range of illnesses from asymptomatic (subclinical) infections to acute respiratory illnesses and fatal encephalitis.  But despite our many brushes with Nipah, there still remains a lot that is unknown – we still need to know more for instance, about how the virus spills over from bats to humans, and why this is happening. There’s also the growing concern of the surge in zoonotic infections across the country – scrub typhus and leptospirosis for instance, and why this is happening.