Nipah virus: What we know and how Australian researchers are responding

Nipah virus has recently re-entered global conversations following an outbreak in India. Although the virus is not present in Australia, it continues to cause small but serious outbreaks overseas. 

At CSIRO, researchers are studying Nipah virus and related bat-borne pathogens to strengthen national preparedness and build the scientific knowledge needed to respond swiftly to new pathogen threats. Only a few months ago, CSIRO announced the discovery of a previously unknown virus in the same family as Nipah virus, underscoring Australia’s ongoing research focus on this group of high‑consequence pathogens. 

CSIRO researchers Dr Sarah Edwards and Ms Jenn Barr explain what we know about Nipah, how transmission happens and how Australian science contributes to global efforts to monitor and understand emerging viruses. 

What is Nipah virus? 

Dr Sarah Edwards, Group Leader — Zoonotic Pathogens and Models, CSIRO: 

Nipah virus is a highly pathogenic zoonotic virus — meaning it spreads from animals to humans — that can cause severe respiratory illness and fatal brain inflammation (clinically known as encephalitis). First identified in 1998, it is considered one of the most dangerous emerging infectious diseases due to its high fatality rate and lack of approved treatments or vaccines. 

While Nipah virus is not currently present in Australia, we do have closely related viruses, including Hendra virus, which is carried by Australian flying foxes. Hendra virus can spillover — that is, jump from its natural animal host into another species — from bats to horses, and infected horses can then transmit the virus to humans. At present, there is no evidence of direct transmission of Hendra virus from bats to humans. 

Why is there an outbreak now? Is this outbreak a new strain? 

Dr Sarah Edwards, Group Leader — Zoonotic Pathogens and Models, CSIRO:

Nipah virus outbreaks occur almost annually in parts of Asia — most often India and Bangladesh. The current outbreak in India is not caused by a new strain of the virus, however it is occurring in an area (West Bengal) that has not seen cases of Nipah virus for nearly 20 years. 

Are there differences between the virus in Bangladesh and India? 

Dr Sarah Edwards, Group Leader — Zoonotic Pathogens and Models, CSIRO:

The viruses being reported in Bangladesh and India are closely related but not identical. The main difference is in how spillover occurs. In Bangladesh, cases are often seasonal and linked to the consumption of contaminated sap from date palms. In India, Nipah virus outbreaks occur occasionally. When they do happen, the infections are usually linked either in healthcare settings (for example, the virus spreading between patients or healthcare workers in hospitals) or to exposure to bats. 

Despite these differences, both regions experience severe disease and high fatality rates during outbreaks. 

How is Nipah virus transmitted? 

Ms Jenn Barr, experimental scientist and leader Pathogen Investigation team, CSIRO:

Transmission of Nipah virus occurs through several well-established pathways. 

Animal to human transmission can happen when people come into direct contact with infectious bodily secretions such as the saliva, urine or faeces of fruit bats or infected intermediate hosts like pigs. 

Contaminated food also plays a significant role in transmission, particularly date palm sap (a delicacy) that is partially consumed by bats. For example, in Bangladesh, fruit bats often drink from or lick date palm sap collection pots, contaminating the sap with their saliva or urine and creating a well-known route of human infection. 

Nipah virus spreads from person-to-person through close contact with an infected individual or by exposure to their bodily fluids. 

Could this Nipah virus outbreak affect animals or people in Australia? 

Ms Jenn Barr, experimental scientist and leader Pathogen Investigation team, CSIRO:

There have been no recorded outbreaks of Nipah virus in Australia to date. It is highly unlikely that animals or people in Australia will be affected by the current outbreak as the virus does not spread easily between people and requires close, prolonged contact with infected individuals. 

Nipah virus is extremely rare, with isolated outbreaks occurring almost exclusively in Bangladesh and India. Despite its high fatality rate and significance as an unpredictable outbreak threat, Nipah virus spreads poorly between people and lacks airborne transmission. Consequently, outbreaks of this virus tend to remain localised, driven primarily by spillover events, and are usually effectively contained with existing public health measures to limit further spread. 

What Nipah virus research is CSIRO doing? 

Dr Sarah Edwards, Group Leader — Zoonotic Pathogens and Models, CSIRO:

CSIRO’s ACDP facility has been focusing efforts on Nipah virus research since the initial outbreak in 1998. This research is broad and spans many different areas including the development of diagnostic tests for early detection, understanding the virus and why it can be so deadly to humans and animals, development of testing models to understand how the virus behaves, carrying out early-stage studies to evaluate potential vaccines and therapeutics, and field surveillance both domestically and internationally. 

How does CSIRO’s ACDP study viruses like Nipah safely? 

Dr Sarah Edwards, Group Leader — Zoonotic Pathogens and Models, CSIRO:

All work with Nipah virus must be conducted in specialised infrastructure, a Biosafety Level 4 laboratory, which is the highest biosafety level in the world. Pathogens that require this level of containment cause severe or fatal disease and have no licenced vaccines or therapeutics available. Scientists working at ACDP undergo extensive biosafety training and wear fully encapsulating suits when researching pathogens like Nipah and Hendra virus. 

Why do so many outbreaks seem to start with bats — how can they carry so many viruses? 

Ms Jenn Barr, experimental scientist and leader Pathogen Investigation team, CSIRO:

Bats don’t necessarily carry more diseases than other animals but some of the viruses they host can be especially harmful to humans. 

Spillover events are often driven by human activities — when natural habitats are reduced or disrupted, wildlife is forced into closer contact with people and livestock. As habitat loss increases and human-wildlife interactions become more frequent, the risk of spillover rises. In contrast, healthy, intact ecosystems help buffer and reduce the emergence of new diseases. 

Why don’t bats get sick from viruses that are deadly to humans? 

Ms Jenn Barr, experimental scientist and leader Pathogen Investigation team, CSIRO:

When humans become infected with a virus, part of what makes us feel unwell is our own strong inflammatory response. Many of the symptoms we experience — like those during a common cold — stem from human immune systems ramping up to fight the infection. 

Bats, however, respond very differently. Their immune systems avoid overreacting by suppressing biological pathways that would otherwise trigger damaging inflammation. CSIRO research has found that some components of the Australian flying fox immune system are already active before infection occurs. This gives them an early advantage, eliminating the delay between encountering a virus and activating their defences. 

What should people do if they find a sick/trapped bat? 

Ms Jenn Barr, experimental scientist and leader Pathogen Investigation team, CSIRO:

Whilst most viruses that bats carry are unlikely to be transmitted directly to humans, it’s important never to handle a bat. Bats can carry Australian bat lyssavirus, which can be transmitted through a bite or scratch.

If you encounter an injured or distressed bat, the safest approach is to contact a wildlife rescue organisation, who can arrange for a vaccinated and trained rescuer to assist.