Nipah is considered a newly emerging deadly virus — scientists only found out that it could jump from bats to other species, including humans, within the past 20 years. The disease is currently incurable and can be transmitted from person to person. It has killed between 40% and 75% of infected people in most outbreaks.
These statistics indicate that Nipah has the potential to cause a deadly pandemic, which is why the World Health Organisation lists Nipah as an urgent research priority, alongside diseases like Ebola and SARS.
Of the nine people who have died so far in the city of Kozhikode in Kerala, three cases of Nipah have been confirmed. Results from the other six are still being tested, and at least 25 more people have been hospitalised.
Nipah first appeared in Malaysia in 1998, when 265 people became infected with a strange illness that caused encephalitis, or brain inflammation, after they came into contact with pigs or sick people. In that outbreak, 105 people died, a fatality rate of 40%.
Since then, there have been a number of smaller outbreaks in India and Bangladesh, with about 280 infections and 211 deaths — an average fatality rate of 75%.
When the first infections jumped from pigs to humans, authorities killed more than a million pigs to try to stop the spread of the disease. Since then, however, researchers have identified several fruit bat species as the natural hosts of the virus. In some cases, humans have been infected after drinking sap from date palms that bats may have contaminated.
The BBC reported that in the most recent outbreak, mangoes bitten by bats were found in a home where three of the deceased patients lived.
Symptoms for Nipah have varied depending on the outbreak. Many patients first experienced fever and headache, followed by drowsiness and confusion. Some patients have also shown respiratory problems and flu-like symptoms while infected. In other cases, symptoms progressed to a coma within a day or two.
People who survive the initial infection can have lasting health issues, including personality changes and persistent convulsions. In some cases, the virus has re-activated in patients months or years after exposure, causing illness and death.
Close contact with sick animals or people can spread the disease — in the current outbreak, at least one of the deceased people was a nurse who treated sick patients. A study of Nipah virus transmission suggested that infected patients' saliva is likely to spread the infection.
For now, the priority is to identify the remaining Nipah cases to ensure the disease doesn't continue to spread.