WHO points to India as the likely source of Australia’s first reported human case of H5N1 bird flu

World Health Organisation reported that the child diagnosed with H5N1 had travelled to Kolkata in India last month.

BySumit Jha

Published Jun 09, 2024 | 12:09 PM Updated Jun 09, 2024 | 12:09 PM

H5N1 australia India

With Australia reporting its first human case of H5N1 bird flu, the World Health Organisation (WHO) said the source of the infection could be India.

WHO reported that the child diagnosed with H5N1 had travelled to Kolkata in India last month. Despite this, the family claimed they had no known exposure to infected individuals or animals while in India.

On 22 May, Australia’s International Health Regulations (IHR) National Focal Point (NFP) notified WHO of a confirmed human infection with the avian influenza A (H5N1) virus. This marked the first confirmed human case of avian influenza A (H5N1) reported by Australia.

Although the source of the infection remains unknown, WHO suggested that exposure likely occurred in India, where this strain of A (H5N1) has previously been found in birds.

Under the IHR, any human infection by a novel influenza A virus subtype, which has the potential for significant public health impact, must be reported to WHO.

“Based on the available information, WHO assesses the current risk to the general population posed by this virus as low,” the organisation stated.

WHO said this was the first human infection with an avian influenza A (H5N1) virus reported by Australia.

“Most human cases of infection with avian influenza viruses reported to date have been due to exposure to infected poultry or contaminated environments. Currently, the likely source of exposure to the virus in the case remains unknown but likely occurred in India where the patient travelled before the onset of illness,” said WHO.

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First human case of H5N1 in Australia

On 17 May, the WHO Collaborating Centre (WHO CC) for Reference and Research on Influenza in Australia notified the NFP of Australia of a suspected case of human A(H5N1) avian influenza (HPAI) in Melbourne in Victoria.

The Department of Health Victoria confirmed this case on 18 May. Under Article 44, the NFP of Australia advised the NFP of India of the confirmed case on 21 May. Under Article 8, the IHR NFP of Australia notified WHO of the case on 22 May.

“The case is a 2.5-year-old female child with no underlying conditions. She had a history of travel to Kolkata, India from 12 to 29 February, 2024. She returned to Australia on 1 March, 2024,” said the WHO.

Upon returning to Australia, the child was presented at a hospital in Victoria on 2 March, where she received medical care and was admitted on the same day.

On 4 March, the patient was transferred to the intensive care unit (ICU) at a referral hospital in Melbourne due to worsening symptoms, for one week. The patient was discharged from the hospital after a 2.5-week admission. The case is now reported to be clinically well.

The Department of Health Victoria reported on 23 May that the family advised that the child started to feel unwell on 25 February, with loss of appetite, irritability and fever, and was taken to a doctor in the evening of 28 February, while in India.

She was febrile, coughing and vomiting and was given paracetamol. The family did not report to the Australian airport biosecurity officer that the child was unwell when she arrived in the country on 1 March.

Additional information provided by the family indicates that the case did not travel outside of Kolkata, and did not have any known exposure to sick persons or animals while in India. It is understood that no close family contacts of the case in Australia or India developed symptoms, as of 22 May.

A nasopharyngeal swab and endotracheal aspirate taken on 6 and 7 March tested positive for influenza A at the referral hospital.

The samples were sent to the WHO CC for further characterisation on 3 April, as there was insufficient knowledge from the referring practitioners at the hospital to connect the case to the H5N1 virus.

The virus genetic sequence obtained from the samples confirmed the subtype A(H5N1) and indicated that the haemagglutinin (HA) gene belonged to clade, which circulates in Southeast Asia and has a history of previous human and poultry infections.

The influenza

Animal influenza viruses normally circulate in animals but can also infect humans. Infections in humans are primarily acquired through direct contact with infected animals or contaminated environments.

Influenza A viruses can be classified as avian influenza, swine influenza, or other animal influenza viruses depending on the original host.

Avian influenza virus infections in humans may cause diseases ranging from mild upper respiratory tract infection to more severe disease and could be fatal.

Conjunctivitis, gastrointestinal symptoms, encephalitis and encephalopathy have also been reported. There have also been several detections of A (H5N1) virus in asymptomatic persons with exposure to infected birds.

Laboratory tests are required to diagnose human infection with influenza. WHO periodically updates technical guidance protocols for the detection of zoonotic influenza using molecular methods like Reverse transcription polymerase chain reaction (RT-PCR).

Evidence suggests that some antiviral drugs, notably neuraminidase inhibitors (oseltamivir, zanamivir), can reduce the duration of viral replication and improve prospects of survival in some cases.

From 2003 to 22 May, 2024, 891 cases of human infections with avian influenza A (H5N1), including 463 deaths, have been reported to WHO from 24 countries. Almost all of these cases have been linked to close contact with infected live or dead birds, or contaminated environments.

India has reported detections of avian influenza A (H5N1) in domestic birds in 2024 to the World Organisation for Animal Health (WOAH).

As the virus continues to circulate in poultry, the potential for further sporadic human cases remains.

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Health Ministry initiates epidemiological investigation

In this case, the exposure likely occurred in India where this clade of A (H5N1) viruses has been detected in birds in the past, although the likely source of exposure to the virus is currently unknown.

Meanwhile, on receipt of information from IHR NFP Australia, the Ministry of Health and Family Welfare of the Government of India initiated an epidemiological investigation with the participation of all relevant sectors.

Human infection can cause severe disease and has a high mortality rate. These A (H5N1) influenza viruses, belonging to different genetic groups, do not easily infect humans, and human-to-human transmission thus far appears unusual.

As the virus continues to circulate in poultry, particularly in rural areas, the potential for further sporadic human cases remains.

Currently, available epidemiological and virological evidence suggests that A (H5) viruses have not acquired the ability of sustained transmission among humans, thus, the likelihood of human-to-human spread is low.

(Edited by Muhammed Fazil)