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Why is H5N1 so deadly? Uncover the real dangers of the deadliest subtype of bird flu!
Avian influenza, also known as bird flu, is a disease caused by the influenza A virus that mainly affects birds but sometimes also affects mammals, including humans. The primary reservoir of avian influenza is wild waterbirds, and the pathogen is endemic in many bird groups. Symptoms of avian influenza vary depending on the subtype of the virus and the bird or mammalian species affected.
Based on the severity of the virus' impact on poultry, avian influenza viruses can be divided into low-pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI). In chickens, LPAI will show mild or no symptoms, while HPAI can cause severe respiratory distress and sudden death.
It is particularly noteworthy that a particularly aggressive subtype, H5N1 (A/H5N1), is a huge potential threat and has already had a devastating impact on poultry. As H5N1 spreads, an estimated half a billion farm poultry have been slaughtered to curb the spread of the virus. The existence of this highly pathogenic avian influenza not only poses a threat to agriculture, but also raises concerns about human health, because prolonged close contact with infected birds can lead to human infection with avian influenza.
The dangers of highly pathogenic avian influenza
Since 1981, a classification system has been established globally to assess the impact of avian influenza. This system classifies avian influenza subtypes into highly pathogenic and low pathogenic, a classification determined by the lethality of a particular virus in chickens. However, for other species, this classification does not ensure accurate prediction of symptoms after infection.
The WHA (World Health Assembly) has required that all tests of LPAI H5 and H7 be reported since 2006 because they may mutate into highly pathogenic influenza viruses under certain circumstances.
Biological characteristics of influenza viruses
The cause of avian influenza is influenza A virus. This type of virus has a genome composed of negative-sense single-stranded RNA and contains 11 viral genes. The particle size of the virus is 80 to 120 nanometers and is oval or filamentous. Evidence shows that the virus can survive for long periods of time in aquatic environments and can tolerate long-term freezing.
Epidemiology of H5N1
H5N1 was first reported in a small poultry epidemic in 1959, and the pathogen has since continued to spread in poultry and wild birds around the world. According to the World Health Organization, between 2003 and November 2024, 948 confirmed H5N1 cases and 464 deaths have been reported globally. Nonetheless, many mildly symptomatic cases may go undiagnosed.
Symptoms of human infection with H5N1 range from mild to severe, and to date, no cases of sustained human-to-human transmission have been detected.
Development and application of vaccines
For poultry, vaccination against specific HPAI influenza subtypes is possible, however, it needs to be supplemented by other control measures such as surveillance, early detection and biosecurity. There are multiple "candidate vaccines" under development for H5N1 and H7N9 subtypes, which will be quickly tested, licensed and produced if an epidemic occurs.
Potential threat to public health
The mutation rate of avian influenza viruses is relatively high, which makes the coexistence of H5N1 and H7N9 even more worrying. In this case, the virus may acquire new characteristics and even have the ability to infect humans. To date, H5N1 and H7N9 are still considered to be the most disastrous subtypes. Among them, the prevalence of H7N9 in the poultry market and its potential risk of cross-transmission pose a continuing threat to public health.
Global surveillance agencies such as the Global Influenza Surveillance and Response System (GISRS) are continuously tracking the spread of influenza in order to formulate complete control policies for the international community. As influenza virus mutations continue to exist, we can't help but think about how we can better protect ourselves and avoid the spread of potentially dangerous diseases in future prevention and control?
