The Nipah virus doesn’t spread in predictable waves or seasonal patterns. Instead, it emerges at the intersection of ecology, climate, and human behavior – often appearing only after crossing the barrier between animals and people. This unpredictable nature poses a significant challenge to global health security, as early detection is crucial for containing outbreaks.
Researchers across South and Southeast Asia are now combining environmental surveillance – particularly analyzing wastewater and surface water – with bat ecology, land-use data, and climate analysis. The goal is to detect early warning signs of Nipah virus circulation before human cases emerge, offering the potential for proactive intervention rather than reacting after outbreaks become deadly.
Deforestation, agricultural expansion, and climate-driven habitat loss are forcing fruit bats of the Pteropus genus to increasingly come into contact with farms, livestock, and human settlements. Scientists warn that traditional surveillance methods are no longer sufficient in this changing landscape. This requires a shift in perspective – attempting to detect viral signals in water, soil, and other environmental samples, while field researchers track bat roosts, movements, and interactions in landscapes increasingly fragmented by human activity.
“So why does Nipah actually challenge the way we usually do surveillance?” asked Erik Karlsson, head of the virology unit at the Pasteur Institute of Cambodia. “Part of the problem is that it simply doesn’t behave the way most systems expect a virus to behave.”
Unlike pathogens that appear regularly and follow discernible patterns, Nipah outbreaks are rare and highly localized. They are often detected late, Karlsson explained, after transmission has already occurred.
The World Health Organization designated the Nipah virus (NiV) as a priority pathogen in 2018 due to its high fatality rate, zoonotic transmission, and pandemic potential. With no approved vaccine or targeted treatment available, and outbreaks remaining rare but unpredictable, Nipah continues to pose a serious threat to global health.
Concerns resurfaced in late January after Indian authorities confirmed at least two cases of Nipah in West Bengal, prompting heightened alerts across South and Southeast Asia.
In Cambodia, the Ministry of Health responded by strengthening preventive measures against potential cross-border transmission. On January 28, Minister of Health Chheang Ra inspected health control measures and emergency response systems at Techo International Airport, alongside officials from aviation, border control, and health authorities.
Lethality Rates Reaching 75%
The virus was first identified during an outbreak in Malaysia in 1998. Since then, the majority of human cases have been reported in India and Bangladesh, where outbreaks are sporadic but often fatal, with fatality rates estimated by the WHO to be between 40 and 75 percent.
The situation is further complicated by the virus’s zoonotic cycle, which is deeply influenced by environmental changes. Nipah doesn’t follow a simple, traceable path from animals to humans. It can spread through contaminated food, shared environments, and daily human practices, influenced by land use and ecological disruptions.
“It sits right at the intersection of ecology, environment, and public health,” Karlsson said. “That’s precisely what makes it so difficult to monitor.”
Environmental surveillance is designed to work where clinical surveillance cannot – before people become sick. Researchers analyze wastewater, surface water, soil, air, and high-touch surfaces for Nipah virus RNA, the genetic material that serves as the virus’s fingerprint. It’s crucial to note that this doesn’t necessarily mean infectious virus is present.
“When we talk about RNA, we’re not talking about infectious virus,” Karlsson emphasized. “Detecting genetic material doesn’t mean someone can be infected from it.” Viral RNA can persist even after the virus itself has degraded, leaving evidence of its past presence in the system.
This distinction is essential, he explained, as environmental detections are sometimes mistakenly interpreted as signs of active outbreaks. Finding RNA in water or other samples doesn’t mean people are currently infected, but rather provides indications of where and when the virus has circulated – information that can help identify increasing risk.
“It’s not just about public health. It’s about animal health and environmental health, all happening at the same time. Environmental signals aren’t diagnostics – they’re clues. They help us understand the risk,” Karlsson said. “Environmental surveillance works upstream. It’s an early warning layer, not a clinical tool. It helps us see a potential danger before people arrive at the hospital.”
How long the Nipah virus – or its genetic material – persists in different environments is therefore a crucial research question, Karlsson added, as this persistence makes early detection possible.
Two Nipah Virus Lineages in Cambodia
Surveillance is further complicated by the genetic diversity of Nipah. The virus has two distinct lineages, each associated with different transmission dynamics. One lineage has historically been linked to transmission involving livestock, particularly pigs. The other is more often associated with direct bat-to-human transmission and has been responsible for documented human-to-human transmission, particularly in healthcare settings where close contact is frequent.
Pteropus bat Photo lonelyshrimp — Wikipedia
“What’s particularly important is that both lineages are circulating in Cambodia.” In some countries, only one lineage is present. In Cambodia, researchers are encountering both, increasing the stakes for accurate detection.
Environmental and wastewater surveillance relies on laboratory tests – analyses designed to detect Nipah virus RNA. These tests must be able to identify both lineages, Karlsson warned. If they are tailored to only one, critical signals may be missed. “You complete up creating blind spots in the system.”
While laboratory detection is essential, scientists emphasize that it cannot function alone. Understanding where risk emerges requires detailed knowledge of bat ecology and evolving landscapes.
“It really starts with a clear vision of the landscape,” said Farah Ishtiaq, principal investigator at the Tata Institute for Genetics and Society in Bengaluru, India. “Where the bats are, where outbreaks have happened in the past, and where people are getting infected – that contextual information matters more than we sometimes admit.”
Ishtiaq explained that the approach relies on close collaboration between molecular biologists and field researchers. Ecologists track the seasonality of bats, their feeding behaviors, and movements between roosts – patterns increasingly shaped by forest fragmentation, agricultural expansion, and climate stress.
“Changes in land use are altering where bats move and how they interact with humans,” she said. “Much of the viral genetic change we’re seeing in bats is happening under these environmental pressures.”
Despite the central role of bats in Nipah ecology, significant gaps remain. Researchers still lack comprehensive data on roost locations, their stability over time, and how bats move between each other as landscapes evolve. Studies on the interactions between bats, other animals, and human-altered environments also remain limited.
“If we could combine ecological knowledge with basic, consistent, and ongoing surveillance,” Ishtiaq said, “we would be in a much better position to anticipate areas where outbreaks are likely to occur.”
Preventing interspecies transmission, Karlsson added, ultimately requires integrating environmental signals with social realities. How populations cultivate, collect food, handle animals, and share space with wildlife strongly influences risk.
Together, this knowledge enables targeted interventions – risk communication, behavior changes, and prevention strategies tailored to the right places and communities. For a virus as elusive as Nipah, scientists believe this combination represents the best chance of staying ahead, listening for early warning signals not only in hospitals, but in the environments where interspecies transmission begins.
By Sonny Inbaraj Krishnan
With permission from Cambodianess who allows us to offer this article to a French-speaking readership.
