WHO: Australia’s First Case of H5N1 Bird Flu Likely Linked to India

Australia has reported its first human case of H5N1 bird flu, and the World Health Organisation (WHO) suggests that the source of the infection could be India. This development has raised concerns about the spread of the virus and its implications for public health.

H5N1
The Incident

Australia’s International Health Regulations (IHR) National Focal Point (NFP) notified WHO. They confirmed a human infection with avian influenza A (H5N1) on 22 May. This marked the first confirmed human case of avian influenza A (H5N1) reported by Australia. WHO reported that the child diagnosed with H5N1 had traveled to Kolkata, India, last month. Despite this, the family claimed they had no known exposure to infected individuals or animals while in India.

Travel and Initial Symptoms

The case involves a 2.5-year-old female child with no underlying conditions. She had traveled to Kolkata, India, from 12 to 29 February 2024. She returned to Australia on 1 March 2024. Upon returning to Australia, the child visited a hospital in Victoria on 2 March. Doctors admitted her and provided medical care the same day.

The Department of Health Victoria reported that the child started feeling unwell on 25 February. She had a loss of appetite, irritability, and fever, and saw a doctor on 28 February in the evening 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.

Hospitalization and Diagnosis

On 4 March, doctors transferred the patient to the ICU at a referral hospital in Melbourne. The patient stayed in the ICU for one week due to worsening symptoms. The hospital discharged the patient after a 2.5-week admission. Now, the medical report states that the patient is clinically well. A nasopharyngeal swab and endotracheal aspirate taken on 6 and 7 March tested positive for influenza A at the referral hospital.

Genetic Analysis

The hospital sent the samples to the WHO Collaborating Centre for further analysis on 3 April. The referring practitioners lacked sufficient knowledge to connect the case to the H5N1 virus. The samples confirmed the subtype A(H5N1) and indicated the hemagglutinin (HA) gene belonged to clade 2.3.2.1a. This clade circulates in Southeast Asia and previously infected humans and poultry.

Source of Infection

The source of the infection remains unknown. WHO suggested exposure likely occurred in India, where this H5N1 strain was previously found in birds. The family advised that the child 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.

WHO’s Assessment

WHO assesses the current risk to the general population posed by this virus as low. 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 this case remains unknown but likely occurred in India where the patient traveled before the onset of illness.

Human Infection and Avian Influenza

Infected animals or contaminated environments primarily transmit infections to humans through direct contact. 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).

Treatment and Prevention

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, WHO received reports of 891 human infections with avian influenza A (H5N1). These cases included 463 deaths, reported 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.

Epidemiological Investigation

Upon 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.

H5N1
Potential for Human-to-Human Transmission

Available evidence suggests A (H5) viruses haven’t acquired sustained transmission ability among humans. Thus, the likelihood of human-to-human spread is low. However, as the virus continues to circulate in poultry, particularly in rural areas, the potential for further sporadic human cases remains.

This case highlights the importance of monitoring and controlling the spread of avian influenza viruses. It also underscores the need for international cooperation and communication to address the risks posed by these viruses. Public health authorities will continue investigating. They will implement measures to protect the population.

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