- Influenza D virus primarily infects cattle but shows potential to infect humans as well
- Studies reveal influenza D can replicate in human respiratory cells and has zoonotic traits
- No standard diagnostic tests exist, risking underdiagnosis and unnoticed human infections
Even as the world continues to grapple with evolving strains of influenza and the long shadow of Covid-19, scientists are turning their attention to a lesser-known but potentially significant viral threat, influenza D. Traditionally associated with cattle and other livestock, this virus is now being closely studied for its ability to infect humans and possibly trigger future outbreaks. Recent findings highlighted in emerging infectious disease research suggest that influenza D virus (IDV) may have the biological capacity to cross species barriers, a hallmark of past pandemic-causing viruses. While no large-scale human outbreaks have been recorded so far, mounting evidence indicates that the virus is already interacting with humans, particularly those in close contact with animals.
Experts warn that the combination of zoonotic potential, limited surveillance, and lack of diagnostic tools could create a dangerous blind spot in global public health systems. For countries like India, where human-animal interaction is widespread due to agriculture and livestock farming, the implications could be especially significant.
So, how serious is this threat, and what does it mean for global and Indian public health preparedness?
What Is Influenza D Virus?
Influenza D is one of four types of influenza viruses and belongs to the Orthomyxoviridae family. Unlike the more familiar influenza A and B viruses that cause seasonal flu in humans, influenza D has primarily been detected in animals, particularly cattle and pigs.
First identified in 2011, the virus has since been found across multiple species, including livestock and wildlife. Its wide host range and ability to circulate silently in animals make it a concern for zoonotic spillover, the process by which viruses jump from animals to humans.
Evidence Of Human Infection Potential
Recent studies provide compelling evidence that influenza D may not be confined to animals. Laboratory research shows that the virus can replicate efficiently in human respiratory cells, with behaviour comparable to influenza A viruses, known for causing pandemics.
Additionally, serological studies have found antibodies against influenza D in people working with livestock, indicating prior exposure. In some studies, a very high proportion of cattle workers tested positive for such antibodies. Experts also warn that the virus may already be spreading under the radar.
Why Global Health Experts Are Concerned
The concern around influenza D stems from a familiar pattern. Past pandemics, including the 2009 H1N1 flu and Covid-19, originated from animal viruses that adapted to humans.
Influenza D shares several worrying characteristics:
- Zoonotic origin: Circulates widely in animals, increasing mutation opportunities
- Efficient replication: Can grow in human airway tissues
- Silent infections: May cause mild or no symptoms, enabling undetected spread
- Diagnostic gaps: Not detected by routine respiratory virus tests
Experts warn that without improved surveillance, the world risks being "fooled" again by an emerging respiratory virus.
Diagnostic And Surveillance Challenges
One of the biggest risks is that influenza D infections may go unnoticed. Currently, there are no widely available standard diagnostic tests for detecting the virus in humans. This creates a dangerous scenario where infections could be misclassified as generic respiratory illnesses or missed entirely. Evidence from broader influenza research already shows that respiratory infections are often underdiagnosed, even when they contribute to mortality. Without targeted testing, early warning signs of an outbreak could be lost.
India's Unique Risk Factors
India's socio-economic and environmental landscape could increase vulnerability to zoonotic viruses like influenza D.
- High Human-Animal Interface: A large portion of India's population depends on agriculture and livestock. Frequent contact between humans and animals creates ideal conditions for cross-species transmission.
- Dense Population: Urban crowding can accelerate the spread of respiratory infections once human-to-human transmission is established.
- Limited Surveillance Infrastructure: While India has strengthened disease monitoring post-Covid, gaps remain in rural and semi-urban regions, particularly for emerging pathogens.
- Climate And Migration Patterns: Changing climate conditions and animal trade routes may influence virus spread and mutation dynamics.
These factors highlight the importance of a "One Health" approach, integrating human, animal, and environmental health surveillance.
Could Influenza D Trigger A Pandemic?
At present, there is no confirmed sustained human-to-human transmission of influenza D. However, scientists caution that the virus has many of the building blocks required for adaptation. Respiratory viruses are particularly dangerous because they spread easily through droplets and close contact. Seasonal influenza alone causes up to 650,000 respiratory deaths globally each year, underscoring the potential impact of any new strain. If influenza D acquires efficient transmissibility among humans, it could pose a significant global health threat.
What Needs To Be Done?
Public health experts recommend several urgent measures:
- Enhanced surveillance at the human-animal interface
- Development of diagnostic tests for early detection
- Genomic monitoring to track viral evolution
- Preparedness planning, including research into vaccines and antivirals
Early intervention could prevent a localized zoonotic spillover from becoming a global crisis.
Influenza D virus may still be under the radar, but it represents a growing concern in the world of infectious diseases. With clear evidence of human exposure, the ability to infect human cells, and significant gaps in detection, the virus embodies the kind of silent threat that has historically led to global outbreaks. For India and the rest of the world, the lesson is clear: waiting for widespread transmission before acting could be a costly mistake. Strengthening surveillance, investing in research, and adopting a One Health approach are essential steps to stay ahead of the next potential pandemic.
Disclaimer: This content, including advice, provides generic information only. It is in no way a substitute for a qualified medical opinion. Always consult a specialist or your own doctor for more information. NDTV does not claim responsibility for this information.
