Dr Ava Easton is Chief Executive of Encephalitis International and a Senior Honorary Fellow, University of Liverpool, UK.

“Enceph-a-what?” I hear you say. “There are so many global threats these days, not another one.  Sigh” … Let me tell you why you should you be bothered about this one.

Encephalitis is inflammation of the brain, caused often by over 100 everyday infections many will be familiar with such as measles, chickenpox, the flu, and the cold sore virus. Some causes are geographically restricted such as West Nile Virus and Japanese encephalitis.  Other causes can include a person’s own immune system attacking their brain in error. 

Each year between 1 and 1.5 million people develop encephalitis, and almost 100,000 die from it. Encephalitis is the fourth leading cause of neurological death and disability in children under the age of five worldwide and the thirteenth leading cause across all age groups. 

Added to this is the impact of climate change on new and emerging infections – viruses such as Zika and Japanese encephalitis are just two examples. The mosquitoes that carry disease are moving into new geographic territories, infecting unsuspecting populations whose immune systems are ill-prepared, resulting in often devastating consequences.

If you speak to those affected by encephalitis they will tell you, “Encephalitis is a thief!” In the same way that we have watched COVID-19 rob people of their lives and loved ones (and yes, Covid causes encephalitis too), encephalitis has quietly been at work for hundreds of years, robbing families of their loved ones, and even in those families when the person survives, it robs them of the person they once knew. Significant numbers of survivors post-encephalitis suffer long-term outcomes and quality of life impacts.

This World Encephalitis Day (Feb 22) we see the publication of a World Health Organization (WHO) report that makes no bones about the burden and impact of encephalitis for those affected; and that it presents a significant, under-recognized, and underestimated global health challenge, with the greatest burden of disease in low to middle income countries (LMICs). 

But there is something else important about this growing public health threat. It is often the first warning we see when new and emerging infections strike. Encephalitis truly is the canary in the coalmine.

When dead birds started falling out of the sky in New York City in 1999 (5,500 crows died in four months that summer) a curious doctor and virologist called Laura Kramer investigated. These birds were dying of inflammation of the brain (encephalitis) and further investigations revealed the cause as West Nile Virus, a mosquito-borne virus that can also cause encephalitis in humans. Since that time, it has spread rapidly across the United States affecting some seven million people with thousands of neuroinvasive cases and deaths as a result.

The University of Georgia is undertaking a modelling project looking at how the swine and pig industry will be impacted should Japanese encephalitis ever hit the United States. It’s been posited that if it did, it could devastate that industry and almost certainly would jump from pigs to humans as it did in 2022 when an unexpected outbreak occurred in Australia.

There are plenty of horror stories from patients in the global north who describe their often lengthy pathway to accurate diagnosis and treatment. But what is the fate of those living in LMICs – it is precisely from these countries we have an absence of data, and limited or no access to diagnostics for the few treatments that do exist for encephalitis.

As an example, rabies kills around 70,000 people each year, 20,000 of whom are in India. When you die of rabies you effectively die of encephalitis. One heartbreaking account in the literature reminds us of the impact in an LMIC – a child admitted to hospital following a dog bite, dead within two hours and abandoned in the mortuary – the “cost of cremating a dead child could be better utilized to feed other hungry mouths” – a harsh reality faced by many parents in the global south. A further tragedy being that the rabies deaths of tens of thousands of people, like many other causes of encephalitis are preventable through vaccine.

Unless substantial political and financial commitments are taken to mobilise the actions outlined by the WHO report, encephalitis will continue to drive avoidable death and disability. These actions include improved surveillance and data, prevention through vaccination, and investments in health planning and research.

The rise of new and emerging infections that often cause encephalitis will undoubtedly be fuelled by other challenges including increased population density, vaccine hesitancy, intensive farming practices/proximity to animals, and climate change.

More recently we have the additional challenges presented by two critical actions since the return to the White House of Donald Trump: the withdrawal of the United States from the WHO which will undoubtedly hinder efforts to provide lifesaving healthcare and combat deadly outbreaks, especially in LMICs; and the appointment of Robert F Kennedy Junior, a vaccine denier and conspiracy theorist, as U.S. health secretary.