Understanding the dynamics of nipah virus (NiV) transmission and outbreaks in India from Kerala’s perspective

INTRODUCTION

The Nipah virus (NiV), a pleomorphic pathogen classified within the Paramyxoviridae family and Henipavirus genus, was first discovered in Malaysia in 1998 and subsequently manifested in Singapore by 1999.¹ Its initial outbreak in India occurred in Siliguri, West Bengal, in 2001, showcased a dire 68% mortality rate. This grim scenario worsened with a catastrophic event in 2007 in the Nadia district of West Bengal, which recorded an overwhelming 100% mortality rate.¹ NiV’s inclusion in the World Health Organization’s (WHO) 2018 Research and Development Blueprint among the top 10 priority diseases was justified due to its propensity to cause substantial public health crises.¹ The resurgence of NiV in May 2018 in the Kozhikode district of Kerala, India, exhibited an alarming case fatality rate of 89%, resulting in 17 tragic fatalities among 18 confirmed cases within a month.² The most recent NiV epidemic, occurring on September 5, 2021, in Kozhikode district, Kerala, resulted in the unfortunate demise of a 12-year-old boy, attributed to his consumption of rambutan fruits procured along the riverbank by his father.³

The transmission dynamics of NiV [Figure 1]⁷ is based on the direct contact with infected humans or animals or eating food or fruits that have come into contact with the bodily fluids of diseased animals, such as pigs and bats.³ G Arunkumar et al.¹ has demonstrated the transmission dynamics in their research and they had shown that the transmission is happening though close contact of the infected individual. So, contact tracing is a key factor in this scenario. G Arunkumar et al.¹ has also mentioned, “Of the 60 environmental samples including partially eaten mangoes, guava and areca nuts with bite marks of bats were collected from the surroundings of the residence and potential work places of the index case, none had evidence of NiV RNA by real time PCR. His pet rabbits and ducks tested negative for NiV” So, origin of this disease is still not clear, but direct transmission picture is quite clear. So, isolation of cases and contact tracing, both are crucial in this disease.

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Figure 1:

Transmission dynamics of Nipah virus. (Adapted and modified with permission with Creative Common License CC BY 4.0, Open Access Article of 2022) (Created with Bio render).

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DISCUSSION

The incubation period of NiV disease spans a wide spectrum across different geographical regions, ranging from as short as 4 days to as long as 2 months.^3,4 Clinical manifestations of the viral infection exhibit significant variability, encompassing instances predominantly characterized by fever and severe cases involving acute encephalitis. Notably, cases in Kerala showcased psycho-neural symptoms such as behavioral distortions, disorientation, and reduced consciousness.⁵ Throughout India, including recent occurrences in Kerala, all NiV outbreaks have propagated through person-to-person transmission. Substantial evidence supports the correlation between the emergence of bat-related viral infections, which are contagious to both humans and animals and the loss of natural habitats for bats.⁵

Following the confirmation of the 2018 outbreak by the National Institute of Virology (NIV) in Pune, the information was swiftly relayed to the World Health Organization (WHO) on May 23, 2018.⁴ The Medical College Hospital (MCH) in Kozhikode emerged as the central facility for admitting suspected NiV cases, with regional healthcare providers explicitly instructed to adhere to strict protocols and it is crucial to manage the cases at designated tertiary care hospitals with appropriate infrastructure.⁶ In response to the NiV infection situation, a multidisciplinary central team, guided by the Union Health Minister, was deployed to conduct a comprehensive review and formulate a response strategy. Comprising experts from diverse healthcare specialties and reputable organizations, this team was well-equipped to address the exigencies of the situation.⁵

Efforts to contain the spread and reduce the fatality rate of Nipah Virus Disease (NiVD) focus on early detection, vigilant monitoring, and swift response to outbreaks that are prone to epidemics. The Government of India, through the Integrated Disease Surveillance Program (IDSP), plays a pivotal role in early detection by offering technical and financial support to all states under the National Health Mission (NHM). Diagnostic techniques, including virus isolation, neutralization, immunohistochemistry, molecular and serological assays, enzyme-linked immunosorbent assays (ELISA), and polymerase chain reaction (PCR) have been extensively employed for NiV detection, with successful NiV isolation achieved through Vero cell culture. The WHO officially declared the cessation of the epidemic status within the state of Kerala by July 1, 2018.⁴

The comprehensive examination of the 2018 Kerala NiV outbreak revealed a staggering 91% case-fatality rate, resulting in 21 mortalities and only two survivors. The majority of the cases were among males with a median age of 45 years. The median incubation period was meticulously determined to be 9.5 days.⁴

CONCLUSION

Efforts to elucidate the origin of NiV infection involved meticulous sampling from incarcerated bat specimens, utilizing techniques such as mitochondrial cytochrome b gene polymerase chain reaction (PCR) for species classification.

Currently, treatment options [Table 1] for NiV primarily focus on supportive care and symptomatic management, particularly in cases involving various complications. The Department of Health and Family Welfare, Government of Kerala, has recommended drugs such as ribavirin, human monoclonal antibody M102.4, remdesivir, and favipiravir for treatment, with details provided in Table 1. In a study by Pallivalappil et al., Ribavirin was administered to over 40% of patients, while 15% initially received intravenous acyclovir, which was subsequently switched to Ribavirin at a dosage of 1200 mg/day (administered in 6 divided doses) and continued for 14 days in survivors.⁴ Convalescent plasma may emerge as a potential therapeutic recourse in severe cases where proven treatment options are unavailable. Preventive measures focus on identifying and isolating infected individuals, promoting rigorous hand hygiene, and advocating the meticulous use of personal protective equipment (PPE) in endemic areas.⁶ Recommendations to combat the situation are highlighted in Table 2.

The recent Nipah Virus Disease (NVD) outbreak highlights the sporadic nature of NiV spillover into the human population, emphasizing the prevalence of NiV infections among the Pteropus medius bat population. The swift and efficient confirmation of the outbreak in India was facilitated by seamless coordination between Virology Research and Diagnostic Laboratories (VRDL) and the Department of Health and Family Welfare, Government of Kerala, within a mere 12 hours of notification.

Capacity-building initiatives under numerous programs, notably the National Centre for Disease Containment’s Integrated Disease Surveillance Program and India’s Global Health Security Agenda, significantly contributed to the successful containment of this outbreak. Continuous efforts to promote early diagnosis, ensure rigorous laboratory confirmation, provide access to top laboratories, and enhance infection control procedures are critical for identifying and managing future instances of NVD.