Nipah virus does not spread in predictable waves or seasonal patterns. It emerges at the fault lines between ecology, climate and human behavior — often appearing only after crossing the barrier between animals and humans. To detect it earlier, scientists are rethinking disease surveillance itself, shifting focus from hospital wards to bat roosts, wastewater systems and rapidly changing landscapes where the risk of cross-species transmission builds silently.
Across South and Southeast Asia, researchers are now combining environmental monitoring — particularly wastewater and surface water analysis — with bat ecology, land use data and climate analysis. The goal is to detect early signs of Nipah virus circulation before human cases appear, providing the opportunity to intervene early rather than reacting after outbreaks become fatal.
As deforestation, agricultural expansion and climate-driven habitat loss force fruit bats of the genus Pteropus moving ever closer to farms, livestock and human settlements, scientists warn that old surveillance models are no longer enough. The answer is a shift in perspective — attempting to detect viral signals in water, soil and other environmental samples, while field researchers track the roosts, movements and daily interactions of bats in landscapes increasingly fragmented by human activity.
« So why does Nipah really 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 classified Nipah virus (NiV) as a priority pathogen in 2018, due to its high case fatality rate, zoonotic transmission, and pandemic potential. In the absence of an approved vaccine or targeted treatment, and with outbreaks remaining rare but unpredictable, Nipah continues to pose a serious risk to global health.
Concerns resurfaced in late January after Indian authorities confirmed at least two cases of Nipah in West Bengal, leading to heightened alerts across South and Southeast Asia.
In Cambodia, the Ministry of Health responded by strengthening preventive measures against possible cross-border transmission. On January 28, Health Minister Chheang Ra inspected health screening devices and emergency response systems at Techo International Airport, alongside aviation, border and health officials.
Case fatality rates of up to 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 case fatality rates estimated by the WHO to be between 40 and 75 percent.
The situation is further complicated by the zoonotic cycle of the virus, deeply influenced by environmental changes. Nipah does not 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 disturbance.
« It lies exactly at the intersection of ecology, environment and public health”Karlsson said. “That’s precisely what makes him so difficult to watch.” »
Environmental monitoring is designed to work where clinical monitoring cannot — before people get sick. Researchers analyze wastewater, surface water, soil, air and high-touch surfaces for Nipah virus RNA, the genetic material that makes up the virus’s blueprint. It is crucial to note that this does not mean that live, infectious virus is present.
« When we talk about RNA, we are not talking about infectious viruses” and insistence Karlsson. «Detecting genetic material does not mean that someone can become 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 critical, he explained, because environmental detections are sometimes misinterpreted as signs of active outbreaks. Finding RNA in water or other samples does not mean people are currently infected. Rather, it provides insights into where and when the virus circulated — information that can help identify an increase in risk.
«It’s not just about public health. It’s about animal health and environmental health, all happening at the same time. Environmental signals are not diagnostics — they are clues. They help us understand the risk,” Karlsson said.“Environmental monitoring therefore works upstream. It is an early warning layer, not a clinical tool. It helps us see 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, because this persistence makes early detection possible.
Two lineages of Nipah virus in Cambodia
Monitoring is further complicated by the genetic diversity of Nipah. The virus has two distinct lineages, each associated with different transmission dynamics. One of the lineages has historically been linked to transmissions 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 transmissions, particularly in healthcare settings where close contact is common.
Bat of the genus Pteropus Photo lonelyshrimp — _Wikipedia
“What is particularly important is that both lineages circulate in Cambodia.” In some countries, only one lineage is present. In Cambodia, researchers encounter both, raising the stakes for accurate detection.
Environmental and wastewater monitoring relies on laboratory tests — analyzes designed to detect viral RNA. These tests must be able to identify both lineages, Karlsson warned. If they are tailored to one, critical signals may be missed. “We end up creating blind spots in the system ».
While laboratory detection is essential, scientists emphasize that it cannot work alone. Understanding where risk emerges requires detailed knowledge of bat ecology and changing landscapes.
« It all really starts with a clear vision of the landscape,” said Farah Ishtiaq, principal researcher at the Tata Institute for Genetics and Society in Bengaluru, India. “Where the bats are, where outbreaks have occurred in the past, and where people are infected — this context information matters more than we sometimes admit. »
Ishtiaq explained that the approach relies on close collaboration between molecular biologists and field researchers. Ecologists track bats’ seasonality, feeding behaviors, and movements between roosts—patterns increasingly shaped by forest fragmentation, agricultural expansion, and climate stress.
«Land use changes are altering where bats go and how they interact with humans,”she declared.“A lot of the viral genetic changes we see in bats occur under these environmental pressures. »
Despite the central role of bats in the ecology of Nipah, important gaps remain. Researchers still lack comprehensive data on the location of roosts, their stability over time, and how bats move between them as landscapes change. Studies examining interactions between bats, other animals, and shared and human-modified environments also remain limited.
« If we could combine ecological knowledge with basic, consistent and continuous monitoring”Ishtiaq said, “we would be in a much better position to anticipate areas where outbreaks are likely to occur. »
Preventing cross-species transmission, Karlsson added, ultimately requires integrating environmental signals with social realities. The way people 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 say this combination represents the best chance to stay ahead of the curve, listening for early warning signals not only in hospitals, but also in environments where cross-species transmission begins.
By Sonny Inbaraj Krishnan
Courtesy of Cambodianess which allows us to offer this article to a French-speaking readership.
date:2026-02-14 00:17:00