No human-to-human transmission among patients with AES: Study

Kochi: A study based on surveillance data from 17 virus research labs in India found that Nipah virus (NiV) outbreaks in Kerala in 2019, 2021, and 2024 showed no human-to-human transmission among patients with acute encephalitis syndrome (AES). This was unlike the outbreaks in 2001, 2007, 2018, and 2023, where patients also had acute respiratory distress syndrome (ARDS).

The two Nipah spillover events in 2024, where no transmission was observed, highlighted the need for better surveillance of ARDS cases to manage and contain outbreaks, said a recent paper in the Elsevier Journal of Infection and Public Health. The paper stated that India intensified NiV surveillance in West Bengal and Kerala, establishing a network of ten and seven trained virus research and diagnostic laboratories (VRDLs), respectively. Since Nov 2024, these laboratories initiated screening for NiV infection among cases of severe acute respiratory illness (SARI) negative for other common endemic viral respiratory pathogens. This targeted approach helps to identify potential NiV cases early, even when they might be masked by similar illnesses.

The study compared the clinical and epidemiological characteristics of AES and ARDS - predominant NiV outbreaks in Kerala to identify factors influencing transmission dynamics and examine public health interventions and their effectiveness in outbreak containment. Researchers from NIV Pune and Kerala, along with the state surveillance unit of the directorate of health services, were involved in the study.

It stated that the characteristic coughing and other respiratory symptoms in ARDS patients generate virus-laden aerosols, which, due to their smaller particle size, can travel greater distances and remain suspended in the air for extended periods, increasing the risk of inhalation and subsequent infection. This contrasts sharply with outbreaks where AES predominates, as seen in 2019, 2021, and 2024. Furthermore, the viral load and shedding patterns in AES cases may differ, potentially contributing to reduced transmissibility.

The study stated that they found the two NiV outbreaks in Malappuram with AES as the predominant clinical manifestation in July and Sep 2024. Among all close contacts screened, no secondary transmission of NiV was observed.