Between late 2022 and early 2023, hospitals in Bangladesh treated five patients exhibiting alarming symptoms reminiscent of the Nipah virus. They experienced high fevers, respiratory distress, and severe brain inflammation. Nipah, a notorious bat-borne virus, has a mortality rate that can reach up to 70%.
However, the PCR tests for these patients returned negative results.
A recent study has since identified the culprit: Pteropine orthoreovirus (PRV). Previously thought to only cause mild illnesses like colds, this new evidence suggests it can have much more severe effects.
A Traditional, Dangerous Practice
For many generations, people in Bangladesh have been harvesting sap from date palms, using clay pots to collect the sweet nectar overnight. It’s a cherished local delicacy.
But they’re not the only ones interested in the sap; Pteropus bats, or the large flying foxes of South Asia, often visit the trees to lick the syrup. Unfortunately, these bats are also key vectors for several dangerous diseases, including Nipah.
When the five patients, all in critical condition, arrived at the hospital, doctors were puzzled. These individuals came from different locations and didn’t know each other. The only connection? They had all recently consumed glassfuls of raw date palm sap while battling serious health issues.
In search of clarity, researchers sent throat swabs to the Center for Infection and Immunity at Columbia University. High-tech sequencing methods confirmed the sap’s link to the infections.
“Our findings suggest that the health risks associated with consuming raw date palm sap extend beyond Nipah virus,” noted Nischay Mishra, PhD, from Columbia University’s Mailman School of Public Health. “This highlights the need for extensive surveillance to pinpoint and address public health threats posed by emerging bat-borne viruses.”
Anatomy of a Master Shifter
PRV was first described about ten years ago, isolated from a flying fox. It’s a non-enveloped virus, lacking the fatty outer layer that makes some other viruses easier to eliminate with soap. Its genome consists of ten segments of double-stranded RNA.
This structured composition is key, allowing the virus to excel at “reassortment.” If two strains infect the same bat, they can mix segments, potentially fostering a new version that is more infectious or harmful to humans.
Worryingly, PRV appears to be more hazardous to humans than once believed.
When researchers followed up with the patients a year and a half later, they found persistent issues. Two survivors still grappled with fatigue and mental fog, struggling physically long after the initial infection. Tragically, one patient from Sirajganj died a year after his health began to deteriorate, succumbing to mysterious neurological complications.
In earlier instances observed in Malaysia and Indonesia, PRV primarily resulted in mild respiratory symptoms. The situation in Bangladesh, however, paints a different picture.
The Viral Lottery
If the emergence of another bat virus is unsettling, it’s a valid concern. Bats are known for their strong immune systems, meaning that viruses surviving within them are often equally resilient and potentially dangerous.
Viruses typically struggle to jump between species—much like a long shot in a lottery. But increased interaction with the host species offers more opportunities for the virus to adapt.
There exists a minimal chance this virus could learn to transmit among humans. PRV strains in Malaysia have already shown limited human-to-human transmission. When considering its genetic adaptability, this could lead to a significant public health disaster.
This gives rise to the necessity for broader monitoring by health professionals. Currently, the focus is primarily on Nipah, and based on this study, that may not be sufficient.
The problem is, enhancing these measures requires more funding and specialists, which is tricky, especially as support from places like the U.S. for such programs is dwindling, posing risks globally. Countries like Bangladesh must receive more backing to manage these threats effectively.
In the meantime, health officials in Bangladesh have been urging the public for years: Stop consuming raw sap. Boiling the sap neutralizes the virus, making it safe to enjoy. Yet, the cultural attachment to the raw flavor complicates any attempts to change this well-established tradition.
Journal Reference: Sharmin Sultana, Ariful Islam, James Ng, Sunil Kumar Dubey, Manjur Hossain Khan, Cheng Guo, Mohammed Ziaur Rahman, Joel M. Montgomery, Syed Moinuddin Satter, Tahmina Shirin, W. Ian Lipkin, Lisa Hensley, Nischay Mishra. Bat Reovirus as Cause of Acute Respiratory Disease and Encephalitis in Humans, Bangladesh, 2022–2023. Emerging Infectious Diseases, 2025; 31 (12) DOI: 10.3201/eid3112.250797
