What Is the Incubation Period of Nipah Virus? Expert Explains Detection Challenges and Symptoms

Several Asian countries have stepped up health screening measures following the detection of two Nipah virus cases in West Bengal, India. Thailand, Singapore, Hong Kong, and Malaysia have introduced enhanced testing and monitoring at airports and other entry points as a precaution.

The Nipah virus is known for its high fatality rate, ranging from 40 to 75 per cent, depending on a country’s ability to detect, trace, and treat infections, according to the World Health Organization (WHO). While the virus can spread from person to person, such transmission is rare, and outbreaks are usually limited and controllable, experts and the European Centre for Disease Prevention and Control say.

Here is what is known about the virus, including how it spreads, its symptoms, and how long it takes to appear.

What is Nipah virus?

Nipah virus is a zoonotic disease that spreads from animals to humans, mainly through fruit bats. It is comparable to viruses such as COVID-19 and Ebola in terms of its potential severity, said Dr Dip Narayan Mukherjee, Consultant in Microbiology and Infectious Diseases at CK Birla Hospitals, CMRI.

According to the WHO, the primary route of infection is through the consumption of fruit or fruit products, such as raw date palm juice, contaminated with saliva or urine from infected bats.

The virus can also spread between people, especially those in close contact. In addition, it can infect animals such as pigs, dogs, cats, sheep, and horses. First identified in 1999 among pig farmers in Malaysia and Singapore, Nipah has since caused recurring outbreaks, mainly in India and Bangladesh.

What is the incubation period?

One of the biggest challenges in controlling Nipah is its unpredictable incubation period—the time between exposure and the onset of symptoms.

Most cases develop symptoms within 5 to 14 days, but in rare instances, the incubation period can extend up to 45 days. During this phase, infected individuals may appear healthy and continue their daily activities, increasing the risk of unnoticed transmission.

The absence of early warning signs makes it difficult to identify cases based on symptoms alone, allowing the virus to spread silently in some situations.

What are the early symptoms?

Early symptoms of Nipah infection include fever, headache, muscle pain, sore throat, and fatigue. These are similar to those of common viral illnesses, which often leads people to ignore them or self-medicate.

Experts warn that mistaking these symptoms for a common cold can delay medical attention and isolation, increasing the risk of transmission.

What are the long-term effects?

About 25 per cent of patients may develop serious brain-related complications, according to Tropical Medicine and Infectious Disease. These include dizziness, confusion, behavioural changes, seizures, and, in severe cases, coma caused by encephalitis.

Some patients may also experience respiratory problems such as cough and breathlessness, which raise the risk of spreading the virus.

The disease progresses differently in individuals. While some deteriorate rapidly after neurological symptoms appear, others may remain stable before suddenly worsening. In some cases, neurological problems can emerge weeks or months later, highlighting the need for long-term monitoring.