It starts with the usual symptoms of an infection: sore throat and fever, headache and muscle pain. But within hours, it is clear that it is more than just flu.
First comes the dizziness and fuzzy thought, then the seizures and, for most, death.
Named after the region in Malaysia where it was first identified 20 years ago, several outbreaks of the Nipah virus have been reported in Bangladesh and India since then, including in Kerala in 2018 when 17 people died from only 18 confirmed cases.
Now the Indian state, already hit hard by the Covid-19 pandemic, is on high alert once more after the death of a 12-year-old boy who contracted the virus.
The danger posed by the virus led to it being added to the World Health Organisation list of infections posing a global threat, putting it in the same threat category as Ebola, Zika and Mers.
While evidence suggests that while it kills up to 75 per cent of those infected, Nipah is still relatively hard to contract.
Previous outbreaks suggest direct contact with infected animals or patients is needed to become infected.
Like Covid-19, which has ravaged Kerala, Nipah is a zoonotic disease that is believed to originate in bats.
In Nipah’s case, fruit bats of the family Pteropodidae are the natural hosts. The animals do not appear to suffer illness as a result.
According to the World Health Organisation, consumption of fruit or fruit products, such as raw date palm juice, contaminated with urine or saliva from infected fruit bats was the most likely source of infection in outbreaks in Bangladesh and India.
Efforts continue to find treatments and vaccines before it evolves into something like the Spanish Flu pandemic that struck exactly a century ago or the Covid-19 pandemic the world is grappling with today.
While far less deadly than Nipah, the Spanish Flu virus spread like wildfire and between 1918 and 1920 killed an estimated 50 to 100 million people worldwide.
The Covid-19 pandemic has a grim global death toll of about 4.6 million from more than 222 million cases.
Science remains key to combating viruses
Yet, as viruses evolve, so does scientific knowledge. And researchers are now starting to get the upper hand in the war against these microscopic terrorists.
When the Spanish Flu epidemic began, the very existence of viruses was unclear. Scientists knew only that some diseases were caused by agents so small they were invisible even using the most powerful optical microscopes.
It took the invention of the electron microscope in the 1930s to reveal their true nature: small strings of molecules wrapped in a protein bag.
Made from either DNA or its close relation RNA, those molecules allow the virus to hijack the genetic machinery of healthy cells and churn out new virus instead.
Lessons from the past offer hope
No one knows where viruses came from. Some scientists have posited that they may be from another world.
What is certain is that they pose a constant threat to life on our planet. Reports of smallpox date back millennia, and during the 20th century alone that one disease claimed at least 300 million lives.
But it was also the first to be defeated by science. In 1980, the WHO announced that its global programme of mass vaccination begun 20 years earlier had finally eliminated the disease.
Ever since, scientists have been working to achieve similar success with other viral killers.
And now there is real optimism that success is within reach.
When the Ebola virus claimed its first victims in central Africa in 1976, it gained a nightmarish reputation. Up to 90 per cent of those infected died horrific deaths, bleeding to death while their organs disintegrated.
In 2013, Ebola tore across West Africa, killing more than 11,000 in a three-year epidemic.
It has since flared up again, claiming victims in the Democratic Republic of Congo. But this time doctors fought back, using an experimental vaccine developed by the German pharmaceutical company Merck.
While the vaccine is not a cure, the hope is that it can dramatically slow the spread of the disease, allowing medics to focus on those infected.
In 2018, the US National Institutes of Health announced the start of human trials of a treatment for another disease on the WHO's most wanted list: Mers.
Early detection is vital
But the most potent weapon in the war against viruses is not a drug or a vaccine, but surveillance.
Early detection of the very first cases allow those affected to be identified and quarantined – thus depriving the viruses of the one thing they all need to thrive: human hosts.
No matter how fast they evolve, if they cannot spread they will become extinct.
Since the WHO’s establishment of a global network of monitoring centres for influenza in 1952, it has arguably saved more lives than any medical treatment yet devised.
And it has probably already prevented at least one global pandemic.
In November 2002, Canadian epidemiologists came across rumours of a new disease that had broken out in southern China.
It was the first evidence for what became known as Severe Acute Respiratory Syndrome (Sars) virus, which proved to be almost as dangerous as Spanish Flu.
By monitoring its spread, epidemiologists were able to help keep it contained, and when the outbreak ended in July 2003, Sars had claimed fewer than 800 lives worldwide.
The virus surveillance system is now so good that it detected the handful of Nipah cases within days, and triggered a global alert.
No one knows when or where the next potential pandemic will start. But our best hope of stopping it lies not in miracle cures, but in vigilance.