Nipah virus resurgence: a call for preparedness across states

Nipah virus (NiV) is a zoonotic disease that was first identified in 1999 during an outbreak among pig farmers in Malaysia [1]. Since then, 749 human cases have been reported across five countries: Bangladesh, India, Malaysia, Singapore, and the Philippines [2]. NiV spreads from bats to humans or from bats to pigs and then to humans. The virus can also spread directly from person to person [3]. Pteropus bats (popularly called fruit bats) are typically the primary reservoir for the virus. However, during the early outbreaks in Malaysia and Singapore, most human infections were owing to direct contact with infected pigs or their contaminated tissues and fluids [3]. The outbreaks in Bangladesh and India were probably caused by the consumption of fruits or fruit products that had been contaminated with the urine or saliva of infected fruit bats (Fig. 1A) [4]. According to the World Health Organization (WHO), individuals infected with NiV commonly show symptoms such as fever, headaches, muscle pain, vomiting, and a sore throat. In some cases, individuals might also develop atypical pneumonia and severe respiratory problems, including acute respiratory distress. In severe cases, encephalitis and seizures can occur. Although many who survive acute encephalitis make a full recovery, some may experience long-term neurological problems (Fig. 1B) [5].

Fig. 1.

An overview of Nipah virus: (A) transmission mechanism; (B) symptom; (C) outbreak history in India and current outbreak in Kerala.

Beginning on 21st July 2024, India experienced its seventh NiV outbreak; this was the fifth in the state of Kerala. A 14-year-old boy from Malappuram in Kerala died after contracting NiV infection. Confirmation was performed by India's apex reference laboratory at the National Institute of Virology, Pune [6]. Over 20 people have died from NiV since 2018 in Kerala [7]. The first ever outbreak of NiV in Kerala's Kozhikode and Malappuram districts during 2018 claimed the lives of 17 individuals (Fig. 1C) [7]. The state government and central government agencies’ management of the outbreak has been recognized as a success by WHO [1]. However, technical difficulties were worsened by the inexperience of surveillance personnel, highlighting sthe need for more trained public health specialists and epidemiologists. Despite technical support provided by the WHO, the documentation and data sharing processes were not satisfactory [1]. Expertise was lacking within the healthcare system in managing infections that spread quickly and could be life-threatening, and hospital infection control protocols were also inadequate. However, until the outbreak of 2023, infectious disease containment efforts against NiV had improved after the COVID-19 pandemic. The training and experience that came out of the COVID-19 pandemic built up the capacity of field workers in terms of contact tracing. Mask use, social distancing, and hand hygiene were practised. Isolation practices and coordination among health authorities enhanced the responses. Decentralized actions and strong political leadership further contributed to rapid containment, and prior NiV outbreaks provided critical insights into effective public health strategies [8].

It is notable that these outbreaks have been happening only in Kerala and in only two districts, Kozhikode and Malappuram. This geographic link has been examined many times. First, Kerala's dense vegetation provides an ideal habitat for fruit bats, which are natural reservoirs of the virus. Additionally, the proximity of human settlements to fruit bat roosting sites owing to urbanization, and disruption of bats’ natural habitat, increase the risk of NiV transmission. Kerala's tropical climate and high humidity levels also favour survival of the virus. Human practices, such as consuming raw date palm sap contaminated with bat secretions, also contribute to transmission [9,10].

Despite Kerala's robust surveillance system, the state continues to experience outbreaks and fatalities annually. The incidence is low, but a single case of NiV is a serious public health threat owing to a high fatality rate (60%–90%) for the variant found in Kerala [8]. The potential for rapid human-to-human transmission and lack of specific antiviral treatment increases the vulnerability toward NiV. Nipah is caused by an mRNA virus that mutates rapidly, potentially altering its transmission dynamics. This characteristic heightens the risk of larger future outbreaks or even a pandemic. [11].

As per a survey conducted in 14 states and union territories (UT) by the National Institute of virology, NiV strains have been found in bats across different states in India including Assam, West Bengal, Bihar, Karnataka, Maharashtra, Goa, Tamil Nadu, Kerala, and two UT's, Pondicherry and Chandigarh [12]. This is concerning because previous outbreaks of NiV have occurred in Kerala, a state with a robust healthcare infrastructure in comparison with other states in India. Kerala has used its strengths, built over the years, to contain these outbreaks [13]. The concern is a lack of clarity regarding the preparedness of other states if such an event occurs. The most likely scenario is that cases might initially go unnoticed, which could escalate into an epidemic-like situation.

NiV diagnosis is also challenging owing to its non-specific early symptoms. Early-stage diagnosis is typically done using real-time polymerase chain reaction tests on samples such as throat swabs, cerebrospinal fluid, and blood. As the illness progresses, antibody detection using enzyme-linked immunosorbent assay is used [14]. Early detection is crucial for effective treatment and to prevent further transmission. NiV should be considered in people who have symptoms consistent with NiV infection and who have been in areas where Nipah is common, such as Bangladesh or India, particularly if they have a known exposure. Strengthening early diagnosis can be achieved by increasing the availability of high-containment laboratories and point-of-care testing, as seen in the 2019 Kerala outbreak where a micro-PCR assay for rapid NiV detection was implemented with the support of NiV Pune [15]. Incorporating differential diagnosis for diseases like dengue and Japanese encephalitis in suspected NiV cases can also improve accuracy in managing seriously ill patients by reducing the possible diagnoses.

Future strategies for states with NiV in bats, like Kerala, where recurring outbreaks are common, should prioritize preventive measures because there is currently no specific treatment or vaccine available against Nipah [16]. The root cause of disease transmission linked to bat encroachment into human habitats and the consumption of contaminated fruits must be addressed [17]. Public awareness campaigns on the risks of consuming raw date palm sap and the promotion of safer food practices are essential for mitigating transmission. Strengthening surveillance of bat populations and monitoring human settlements near bat habitats will enable early detection and prevention. Urban planning should prioritize minimizing human–wildlife contact, preserving natural ecosystems, and establishing buffer zones [18]. Effective management should focus on implementing infection control measures, triaging processes, isolation practices, and comprehensive patient management that includes providing intensive supportive care [7,19]. Social media platforms can play a crucial role in educating communities about risk factors and possible preventive measures, especially within socioeconomically disadvantaged populations [7,19]. The transmission route followed by NiV warrants the adoption of a One Health approach. Kerala effectively contained virus spread by fostering coordination among human health, veterinary, environmental, and public health departments [20]. Enhancing diagnostic capabilities and establishing rapid response mechanisms are also vital components of this approach, which includes healthcare infrastructure improvements for prompt action. Furthermore, fostering international collaboration for sharing data and resources will help to effectively prevent and manage outbreaks in the future [21].

Funding

None.

CRediT authorship contribution statement

Manya Soni: Writing – review & editing, Software. Vijay Kumar: Writing – review & editing, Software, Resources. Mahendra Pratap Singh: Writing – original draft, Conceptualization. Muhammed Shabil: Writing – original draft, Validation. Sanjit Sah: Writing – original draft.