H9N2 is a subtype of the influenza A virus, which causes human influenza as well as bird flu.
Indian scientists have detected the country’s first case of infection with a rare variant of the virus that causes avian influenza, or bird flu. In the December 2019 issue of the Emerging Infectious Diseases journal of the US Centers for Disease Control and Prevention (CDC), scientists of the National Institute of Virology (NIV), Pune, have reported avian influenza A(H9N2) virus infection in a 17-month-old boy in Maharashtra. What is this virus, and is there any cause for serious concern?
The A(H9N2) virus
H9N2 is a subtype of the influenza A virus, which causes human influenza as well as bird flu. The H9N2 subtype was isolated for the first time in Wisconsin, US in 1966 from turkey flocks. According to the US National Centre for Biotechnology Information (NCBI), H9N2 viruses are found worldwide in wild birds and are endemic in poultry in many areas. However, they are somewhat neglected. According to a recent report by NCBI researcher T P Peacock, H9N2 viruses could potentially play a major role in the emergence of the next influenza pandemic. According to the World Health Organization (WHO), with avian influenza viruses circulating in poultry, there is a risk for sporadic infection and small clusters of human cases due to exposure to infected poultry or contaminated environments. Therefore, sporadic human cases are not unexpected.
Human infections rare
H9N2 virus infections in humans are rare, but likely under-reported due to typically mild symptoms of the infections. Cases of human infection have been observed in Hong Kong, China, Bangladesh, Pakistan, and Egypt. One case was detected in Oman recently. The first case globally was reported from Hong Kong in 1998. A total of 28 cases in China have been reported since December 2015. Cases continue to be reported mainly from mainland China and Hong Kong.
The virus has, however, spread extensively among poultry populations. Surveillance for influenza viruses in poultry in Bangladesh during 2008-2011 found H9N2 virus to be the predominant subtype. The virus was also identified in poultry populations in surveillance studies in Myanmar during 2014-16 and Burkina Faso in 2017.
First case in India
The virus was picked up in February 2019 during a community-based surveillance study in 93 villages of Korku tribes in Melghat district of Maharashtra. NIV scientists were looking to determine the incidence of deaths associated with respiratory syncytial virus (RSV) among children under age two. In the process, they identified A(H9N2) virus infection in one boy. The child had fever, cough, breathlessness, and difficulty in feeding for two days after illness onset on January 31, 2019, and was fully immunised with treatment. After a series of confirmatory tests, the findings were reported last month. Dr Varsha Potdar, senior scientist at NIV, is the lead author of the study along with Dr Pragya Yadav and Dr M S Chadha.
The child was not exposed to poultry. A week before showing the symptoms, he had travelled with his parents to a religious gathering. The father showed similar symptoms but could not undergo serologic testing.
A call for surveillance
NIV scientists said H9N2 viruses have been observed in poultry in India several times. Now, identification of the first clinical human case of H9N2 virus infection highlights the importance of systemic surveillance in humans and animals to monitor this threat to human health, they said.
The same concerns were expressed after the first reported case in Oman. “Despite the low pathogenicity of this subtype, the continuing emergence of the virus in unpredicted region and now rise in number of human cases pose a pandemic threat and the need to adopt a multi sector One Health approach, “ Zayid K Almayahi of the Directorate of Health at Oman has said. Almayahi is one of the scientists who authored a study in the International Journal of Infectious Diseases recently, reporting detection of H9N2 infection in a 14-month-old girl in Oman.
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