On June 5 2024, The World Health Organisation (WHO) confirmed the death of a person infected by Avian Influenza A (H5N2), in April 2024.
On May 23, 2024, the Mexico International Health Regulations (IHR) National Focal Point (NFP) reported to PAHO/WHO a confirmed fatal case of a human infection with avian influenza A(H5N2). This is the first laboratory-confirmed human case of infection with an influenza A(H5N2) virus reported globally. However, the current risk of bird flu virus to the general population is low, according to WHO.
In March 2024, a high pathogenicity avian influenza A(H5N2) outbreak was detected in a backyard poultry farm in the state of Michoacán, which borders the State of Mexico. The virus was detected in a 59-year-old residing in the area. On April 24, the case sought medical attention, was hospitalised at the National Institute of Respiratory Diseases in Mexico City, and died the same day due to complications of his condition.
The case’s relatives reported that the case had already been bedridden for three weeks, for other reasons, prior to the onset of acute symptoms. Mexico’s health reported the person to have chronic kidney disease and type 2 diabetes. However, the case had no history of exposure to poultry or other animals. Although the source of exposure to the virus in this case is currently unknown, A(H5N2) viruses have been reported in poultry in Mexico.
No further cases were reported during the epidemiological investigation. Scientists said the case is unrelated to the outbreak of H5N1 bird flu in the United States that has so far infected three dairy farm workers. Australia reported its first human case of A(H5N1) infection in May, noting there were no signs of transmission. It has however found more poultry cases of H7 bird flu on farms in Victoria state.
A study describing the continuous circulation of low pathogenicity avian influenza H5N2 viruses in Mexico and spread to several other countries was published in 2022.
Epidemiology
Animal influenza viruses normally circulate in animals but can also infect humans. Infections in humans have primarily been acquired through direct contact with infected animals or contaminated environments. Depending on the original host, influenza A viruses can be classified as avian influenza, swine influenza, or other types of animal influenza viruses.
Avian influenza virus infections in humans may cause mild to severe upper respiratory tract infections and can be fatal. Conjunctivitis, gastrointestinal symptoms, encephalitis and encephalopathy have also been reported.
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, e.g. RT-PCR. Evidence suggests that some antiviral drugs, notably neuraminidase inhibitors (oseltamivir, zanamivir), can reduce the duration of viral replication and improve survival prospects for some cases.
WHO risk assessment
Whenever avian influenza viruses are circulating in poultry, there is a risk for infection and small clusters of human cases due to exposure to infected poultry or contaminated environments. Therefore, sporadic human cases are not unexpected. Human cases of infection with other H5 subtypes including A(H5N1), A(H5N6) and A(H5N8) viruses have been reported previously. Available epidemiological and virological evidence suggests that A(H5) viruses from previous events have not acquired the ability to sustain transmission between humans, thus the current likelihood of sustained human-to-human spread is low.
There are no specific vaccines for preventing influenza A(H5) virus infection in humans. Candidate vaccines to prevent A(H5) infection in humans have been developed for pandemic preparedness purposes. Close analysis of the epidemiological situation, further characterisation of the most recent viruses (in human and birds) and serological investigations are critical to assess associated risks and to adjust risk management measures in a timely manner.
WHO advice
This case does not change the current WHO recommendations on public health measures and surveillance of influenza.
Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect and monitor virological, epidemiological and clinical changes associated with emerging or circulating influenza viruses that may affect human and animal health and timely virus-sharing for risk assessment.
Edits made by EH News Bureau