​Greater regularity: On the Nipah virus Politics & News

The case of a 42-year-old woman in Kerala testing positive for Nipah virus on May 8 makes it the third such instance being reported from the State’s Malappuram district in the last two years. The earlier cases were detected last year, in a 14-year-old boy on July 21 and a 24-year-old adult on September 15. With the latest detection of Nipah in the State, Kerala has recorded two outbreaks, in the years 2018 and 2023, involving human-to-human transmission, and four spillovers in the years 2019 and 2021, and two events in 2024. In the May 8 event, even though only one person tested positive for Nipah and seven close contacts tested negative, it is a bit early to call it a spillover. Unlike an outbreak, Nipah spillovers are restricted to a single case with no human-to-human transmission. One reason for the absence of human spread is the timely detection of the case and isolation of the patient. The other reason is the clinical presentation. In the case of Nipah virus spillovers, patients who tested positive for the virus had presented with acute encephalitis syndrome (AES), while in the Nipah outbreaks in 2018 and 2023, the index case and at least a few other infected people had presented with acute respiratory distress syndrome (ARDS). Compared with AES, patients with ARDS present with relatively severe conditions with lung involvement. Besides cough, patients presenting with ARDS have higher viral loads, which serve as a surrogate for disease severity. Immaterial of whether blood, urine or cerebrospinal fluid samples test positive or not, throat swab samples generally test positive if a person is infected by the Nipah virus, which again serve as an indicator of human spread in the case of patients with ARDS. The high viral load, the presence of virus in the throat and the tendency to cough make human spread possible. Greater disease severity in ARDS cases is also the reason for the Nipah deaths in 2018 and 2023. There were 17 deaths from 18 cases in the 2018 outbreak, and two deaths from six cases in the 2023 outbreak. A study by the ICMR-National Institute of Virology (NIV) Pune found that the 2018 Nipah virus had small genetic variations from the Bangladesh strain and was able to cause multisystemic disease in a Syrian hamster model resembling human infection.

The Nipah virus is capable of causing different clinical presentations and is endowed with the ability to cause human spread in some cases. This makes a strong case for a quick and thorough genetic study of the virus in humans and bats. With Nipah cases now a very regular occurrence in Kerala, the compulsion to routinely study fruit bats, which are natural hosts for Nipah, cannot be overemphasised. That even the 2018 virus showed small genetic differences from the Bangladesh strain makes it even more important to know whether the virus causing the spillovers without human spread has evolved further. Such studies can be done by more scientists only when the genetic sequences are shared in public databases without any delay.