WHO confirms human case of bird flu in West Bengal

• The World Health Organisation (WHO) said a case of human infection with bird flu caused by the H9N2 virus was detected in a four-year-old child in West Bengal.

• The patient was admitted to the pediatric intensive care unit (ICU) of a local hospital due to persistent severe respiratory issues, high fever and abdominal cramps in February, and was discharged three months later after diagnosis and treatment.

• The patient had exposure to poultry at home and in his surroundings, and there were no known persons reporting symptoms of respiratory illness among his family and other contacts.

• This is the second human infection of H9N2 bird flu from India, with the first in 2019.

• While the H9N2 virus typically tends to cause mild illness, the WHO said that further sporadic human cases could occur as this virus is one of the most prevalent avian influenza viruses circulating in poultry in different regions.

Bird flu (Avian Influenza) 

• Bird flu (Avian Influenza) is a contagious viral disease affecting several species of food producing birds (chickens, turkeys, quails, guinea fowl, etc), as well as pet birds and wild birds. 

• Occasionally mammals, including humans, may contract Avian Influenza, says World Organisation For Animal Health (OIE).

• Avian Influenza has captured the attention of the international community over the years, with outbreaks in poultry having serious consequences on both livelihoods and international trade in many countries.

• India notified the first outbreak of Avian Influenza in 2006. Since then, outbreaks have been reported in many states. The disease spreads mainly by migratory birds coming into India during winter months, September–October to February–March. 

Human infection with Avian Influenza 

• Although most Avian Influenza viruses do not infect humans, some, such as Avian Influenza H5N1, H7N9 and H9N2, are well known to the public because of their implication in serious and sometimes fatal infections in people.

• H5N1, for example, a highly pathogenic AI virus, was initially diagnosed in humans in Hong Kong in 1997. The virus then re-emerged in 2003 and 2004, and spread from Asia to Europe and Africa causing several hundred human cases and deaths, as well as destruction of hundreds of millions of poultry. 

• This Asiatic form of H5N1 triggered concern from scientists and authorities and remains under close surveillance due to its feared pandemic potential if a mutation allows it to be transmitted from human to human.

• Nowadays, due to ongoing circulation of various strains (H5N1, H5N2, H5N8, H7N8, etc), outbreaks of Avian Influenza continue to be a global public health concern.

• From January 1, 2003 to December 21, 2023, a total of 248 cases of human infection with Avian Influenza A(H5N1) virus were reported from four countries within the Western Pacific Region. Of these cases, 139 were fatal.

• As of January 31, 2024, a total of 90 laboratory-confirmed cases of human infection with influenza A(H5N6) virus including 35 deaths were reported to WHO in the Western Pacific Region since 2014. The last case was reported from China on November 25, 2023.

• As of January 31, 2024, a total of three laboratory-confirmed cases of human infection with influenza A(H3N8) virus with one death were reported to WHO in the Western Pacific Region. 

Highly Pathogenic Avian Influenza

• During 2020, Highly Pathogenic Avian Influenza (HPAI) A(H5N1) clade 2.3.4.4b viruses arose from previously circulating influenza A(H5Nx) viruses and spread predominantly via migratory birds to many parts of Africa, Asia and Europe.

• The epizootic (a disease event in an animal population akin to an epidemic in humans) has led to unprecedented numbers of deaths in wild birds and caused outbreaks in domestic poultry. 

• In late 2021, these viruses crossed to North America and subsequently South America in October 2022. 

• Globally, there have been increased detections of A(H5N1) viruses in non-avian species including wild and domestic (including companion and farmed) terrestrial and marine mammals and, more recently in goats and dairy cattle in the US. 

• Avian Influenza A(H5N1) viruses, especially those of clade 2.3.4.4b, continue to diversify genetically and spread geographically. 

• Since 2022, a broader range of wild bird species has been infected globally which has had deleterious ecological consequences and caused mass die-offs in some species. The situation with wild mammals is also worrying, with some species suffering significant mortality events.

• HPAI is an extremely contagious, multi-organ systemic disease of poultry leading to high mortality, and caused by some H5 and H7 subtypes of type A influenza virus.

• HPAI viruses pose a threat to wild birds and poultry globally. HPAI H5N1 viruses are of even greater concern because of their frequent spillover into mammals. 

• Since the beginning of 2021, as many as 28 detections of A(H5N1) in humans have been reported to WHO, including a case who had exposure to dairy cattle presumed to be infected with A(H5N1) virus. 

• Although human infections with HPAI A(H5N1) virus are rare, having unprotected exposure to any infected animal or to an environment in which infected birds or other animals are or have been present can pose a risk of infection. 

• Therefore, people with work or recreational exposures to A(H5N1) virus-infected animals may be at increased risk of infection and should follow recommended precautions.