Recently, hundreds of thousands of poultry were culled across Nepal following the confirmation of avian influenza (commonly known as bird flu) outbreaks. The virus had first emerged in Morang district, eastern Nepal, this year. Moreover, Nepal’s only central zoo was forced to close indefinitely after several captive birds, including owls, vultures and egrets, as well as mammals such as civets and leopard cats, died from bird flu.

According to the Department of Livestock Services, house crows are considered a primary factor in the continued spread of bird flu across the Kathmandu valley. A few months ago, deaths of house crows associated with the bird flu virus were reported in Kirtipur and Taudaha, Kathmandu. Although every bird flu outbreak is accompanied by extensive discussion and debate on preventing further spread among poultry and reducing the risk of human infection from infected chickens, little attention has been paid to the potential role of house crows in transmitting the bird flu virus, including the possibility of direct transmission to humans.

The public remains largely unaware of the potential risk posed by live or dead house crows during bird flu outbreaks. Several scientific studies from South Asia have documented H5N1 virus infections and deaths in house crows. Given that house crows are native to South Asia and live in close proximity to human settlements, an important question arises: Could house crows become an emerging bird flu threat to humans in South Asia?

Influenza, commonly known as flu, is a highly contagious viral respiratory illness caused by influenza viruses. It is primarily transmitted through respiratory droplets released when infected individuals speak, cough or sneeze. There are four types: A, B, C and D. Among these, A and B viruses are responsible for seasonal epidemics each year. Influenza A comprises multiple bird flu subtypes, including H5N1, H9N2 and H7N9.

According to the Department of Livestock Services, the current bird flu outbreaks in Nepal are caused by the H5N1 and H9N2 subtypes. Both of these avian influenza viruses have been reported to infect humans. Indeed, the H5N1 subtype caused the first confirmed human death in Nepal in 2019. The patient was believed to have acquired the infection through exposure to a chicken; however, an investigation by experts from the Epidemiology and Disease Control Department (EDCD) and clinicians from Sukraraj Tropical and Infectious Disease Hospital (STIDH) could not conclusively determine the source of transmission. Could infected house crows have been an alternative source of the H5N1 bird flu virus in this case? Although speculative, this hypothesis remains plausible and merits further investigation.

Recent studies in the US have demonstrated that H5N1 can be transmitted to humans through exposure to infected dairy cattle. Despite this evidence, H5N1 transmission from dairy cattle to humans has not been reported elsewhere, perhaps because routine surveillance and testing in cattle have not yet been implemented. A few years ago, I observed poultry farmers and their family members presenting with influenza-like illness after dozens of chickens on their farms died each day from an outbreak that was later confirmed to be caused by the H9N2 bird flu virus. However, these patients could not be tested for bird flu viruses because diagnostic testing was not readily available, and it was unclear where such testing could be performed. Given that H9N2 is one of the viruses driving the current large-scale bird flu outbreaks in Nepal, the relevant authorities should raise awareness among high-risk groups.

Most importantly, the Department of Livestock Services has recently reported that the ongoing widespread bird flu outbreaks are linked to house crows, which could facilitate viral spread through close contact with or by sharing food and water sources. The bird flu virus in house crows has been widely reported in South Asia. Because house crows are obligate commensals that live in close proximity to human settlements, the potential for bird flu virus transmission from infected house crows to humans should not be overlooked.

As bird flu is increasingly recognised as a potential future pandemic threat, the possible role of previously overlooked transmission pathways, such as house crows, warrants greater attention. Unlike domestic poultry, house crows are free-ranging, and their movements cannot effectively be controlled, presenting a unique challenge for disease prevention. Failure to develop effective strategies to address the potential role of house crows in bird flu transmission could increase the risk of human infection, and leave South Asia among the region’s most vulnerable to highly pathogenic avian influenza. This underscores the need for innovative One Health approaches to surveillance, risk assessment and outbreak control, by fostering collaboration among the human, animal and environmental health sectors to achieve more effective and sustainable disease prevention and control.