Lessons from Nipah outbreak in Kerala

NiV outbreaks have so far not led to an enormous number of cases as in respiratory viral infections such as influenza or vector-borne viruses like dengue. In the first recorded outbreaks in Malaysia and Singapore, where the infection in humans was linked to pigs, there were 300 cases and more than 100 deaths.

The worrying dimension about NiV infections is that mortality (more accurately, case fatality rate) can range between 40% and 75%. The outcome (mortality) is determined by early diagnosis and good quality supportive treatment since there is no specific curative treatment. In contrast, the case fatality rate for Ebola is over 60%. It has a propensity to infect close family contacts and health care workers through human-to-human transmission; that has been the case in the current outbreak too.

The World Organisation for Animal Health (formerly Office International des Epizooties [OIE]) observed that human cases have occurred sporadically in Bangladesh and India since 2003 without apparent related domestic animal disease outbreaks, suggesting possible human-to-human transmission. NiV can also infect companion animals but it is likely that it does not play any important role in the epidemiology of the disease. It has emerged as a highly localised form transmitted directly to populations without an intermediate amplifying host (pigs). The natural reservoir of NiV is wild fruit-eating bats (Pteropus sp.) that can spill over to human or carrier animals (cat, dog, pig, horse). While it causes mild symptoms in pigs with a mortality of about 1-5%, in human diseases it has a much higher fatality on account of acute respiratory and neurological complications. A critical impact is on the animal husbandry industry for outbreaks linked to pigs; more than 100,000 pigs were killed to contain the Malaysia/Singapore outbreak.

A new wave of zoonotic (diseases transmitted from animals to humans) have emerged towards the turn of this millennium on account of an interplay of several key determinants including large and/or industrial-scale farming, high demand for animal source foods, destruction of forests and wildlife habitats and the climate crisis.

The first NiV outbreak goes back to late September 1998 near the city of Ipoh in the northern Malaysian state of Perak. Initially considered Japanese Encephalitis, (that is linked to pigs and present with similar clinical features) the outbreak could not be halted with the specific measures for JE. It further spread to the southern state of Negeri and then through imported pigs to abattoir workers in Singapore in early March 1999.

The viral genome was sequenced at the Centers for Disease Control and Prevention (CDC) in the US and identified as a new virus. The virus was named Nipah in April 1999 after the river in the town where the first victim lived. The slash-and-burn deforestation for the plantation of palm trees and pulpwood in Malaysia was considered to have displaced bats towards the mango orchards at the edge of pig farms, triggering the chain of events.

Covid-19 prompted the Prime Minister’s Science, Technology, and Innovation Advisory Council (PM-STIAC) to recommend a “One Health Mission” to develop a “unified pandemic preparedness plan” for addressing priority “One Health diseases” (diseases of zoonotic nature, transboundary animal diseases as well as diseases of epidemic/pandemic potential) through cross-ministerial coordination and engage non-governmental stakeholders including academia, private sector and international agencies for “better disease control and preparedness”. One Health is an integrated, unifying approach that aims to sustainably balance and optimise the health of people, animals and ecosystems and recognises that the health of humans, domestic and wild animals, plants, and the wider environment (including ecosystems) are linked and interdependent.

Kerala formulated a One Health Scheme in the context of zoonotic outbreaks such as scrub typhus, Kyasanur forest disease (monkey fever) and Nipah virus disease. The department of animal husbandry and dairying (DAHD) has supported pilots in Karnataka and Uttarakhand to develop a national One Health Framework through early prediction, detection, and diagnosis of zoonoses through increased quality, availability and utility of data evidence. The National Institute of Virology-led surveillance has so far detected evidence of Nipah viral antibodies in bats in Tamil Nadu, Karnataka, Goa, Maharashtra, Bihar, West Bengal, Assam and Meghalaya and Pondicherry.

The G20 Leaders’ Declaration, under the Indian presidency, has pledged to implement the One Health approach, enhance pandemic preparedness and strengthen existing infectious disease surveillance systems. One Health is marked by shared interests where common goals are set and the team works towards benefiting the overall health of a population. It will require sustained collaboration of multiple disciplines and sectors across local, national and global levels. The barriers to effective multi-sectoral engagements are many; carefully thought-out rules of engagement and shared leadership will be the key ingredients to success.

Rajib Dasgupta is professor (Community Health), JNU and co-investigator, UKRI-GCRF One Health Poultry Hub, an international One Health research programme. The views expressed are personal