In this blog post, we’ll explore how avian influenza (the AI virus) spreads, its potential to infect humans, and measures for prevention and response.
What Is Avian Influenza?
Do you remember the avian flu crisis? In 2017, South Korea culled more than 30 million poultry, particularly chickens, to respond to the worst avian influenza outbreak in its history. The government also implemented strict disease control measures, including restrictions on the movement of poultry nationwide for a certain period, which resulted in significant economic and social damage. Along with the massive damage caused by avian influenza, reports of cases transmitted to humans have emerged, making the causative virus and the disease a major global public health concern. We will examine the AI virus and avian influenza, which cause significant damage to ecosystems and economies not only in South Korea but worldwide.
The virus that causes avian influenza is the avian influenza virus (Avian Influenza Virus), commonly referred to as the AI virus.
The AI virus is highly contagious among birds and spreads through various routes. It spreads easily not only through direct contact between birds but also through indirect contact via equipment and materials contaminated with the virus. The virus survives in the vicinity of infected birds’ feces or is shed through saliva, nasal secretions, and eye discharge. In particular, direct contact with contaminated feces is the most common route of infection among birds. Additionally, wild ducks can spread the virus through environments or foraging areas contaminated with their feces, and in poultry farms, infection can also occur through airborne dust and secretions. Since the virus can be detected on the surface of fresh eggshells, the transport of eggs can also serve as a potential means of transmission. Finally, infection can also occur through direct contact with infected birds or surfaces contaminated with the virus.
Avian influenza is a disease that occurs in birds infected with the influenza A virus. The causative virus, influenza A, is classified into various subtypes based on the combination of H and N proteins. Avian influenza A viruses are broadly classified into low-pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI). These viruses circulate naturally among wild waterfowl worldwide and infect various birds, including poultry, as well as some other animals. In particular, they can cause severe illness or death in farmed birds such as chickens, ducks, and turkeys.
The receptors that human influenza viruses primarily bind to are widely distributed in the upper respiratory tract, including the nose, throat, and bronchi. In contrast, the receptors preferred by avian influenza viruses are abundant in cells deep within the lungs. For this reason, even when a person is infected, the virus often does not spread easily to others through coughing, as is the case with seasonal influenza. Consequently, to date, most avian influenza viruses have had limited ability to spread sustainably among humans. However, there have been reported cases where certain viruses have crossed the species barrier to infect humans; the H5 and H7 subtypes are particularly notable examples. So, how do these infections occur?
Influenza A viruses consist of eight separate gene segments. Due to this segmented genome, when different influenza A viruses simultaneously infect the same person or animal, genetic recombination can occur, leading to the creation of a new virus. For example, if a pig is simultaneously infected with a human influenza A virus and an avian influenza A virus, the newly formed virus may be a combination of the genetic information from the original viruses. A virus created in this way has the potential to infect humans and will possess surface proteins different from those of existing influenza viruses. This phenomenon is called “antigenic shift.” If a new virus causes disease in humans and acquires the ability to spread from person to person, there is a possibility of a new global pandemic.
How dangerous is the H5N1 virus?
Among avian influenza viruses that infect humans, H5N1 has been associated with numerous cases of the most severe illness and the highest fatality rates. Infection with H5N1 can lead to severe pneumonia, acute respiratory distress, and shock; in severe cases, it can be fatal. Gastrointestinal symptoms such as nausea, vomiting, and diarrhea are also frequently reported. While most cases of seasonal influenza resolve naturally, H5N1 infection can rapidly worsen, leading to pneumonia, acute respiratory distress syndrome (ARDS), and neurological abnormalities, requiring special caution.
People exposed to infected poultry or suspected farms are subject to thorough monitoring by health authorities. In addition, countries are continuously strengthening their surveillance systems for novel influenza and similar diseases. Although sustained human-to-human transmission is currently very limited, continuous surveillance is being conducted regarding the possibility that the virus could mutate and acquire the ability to spread between humans.
H5N1 infection can occur by inhaling the virus contained in the secretions or feces of infected birds, or by touching contaminated surfaces and then touching the eyes, nose, or mouth. Most human infections reported to date have occurred following close exposure to infected birds or environments contaminated with the virus.
How should we prevent and respond to this?
So, how should South Korea respond to outbreaks of avian influenza and H5N1? Preventive measures for poultry raised on farms include the following.
First, since infection can spread rapidly in intensive farming environments, strict biosecurity measures must be implemented between farms.
Second, to prevent the virus from spreading through overlapping routes of vehicles moving between farms, distribution routes must be clearly managed, and contact with external birds must be minimized as much as possible.
Third, during distribution, it is advisable to simplify the distribution system so that birds from different farms do not share the same vehicle.
In addition, sufficient quarantine personnel must be secured to respond swiftly, and culling must be carried out promptly when necessary. If hygiene management is strictly enforced and routes of viral exposure are thoroughly blocked, the spread of infection between farms can be effectively reduced.
So, how can people protect themselves from wild birds? The most important thing is to follow basic hygiene guidelines. If you have come into contact with birds or visited places where you may have been exposed to the virus, such as poultry markets, you must wash your hands and body thoroughly and maintain strict personal hygiene. In addition, chicken and eggs should be thoroughly cooked, and eggshells should be handled hygienically.
Although the seasonal influenza vaccine does not directly prevent avian influenza, it can help prevent seasonal flu and reduce the risk of co-infection. Currently, avian influenza vaccines for the general public are not routinely administered and are used only on a limited basis for high-risk groups or in specific situations.
Current Research and Future Challenges
Currently, efforts are focused on strengthening disease control measures, raising public awareness of the risks posed by the disease, and developing new treatments and vaccines. Recognizing that existing limited treatments and preventive measures alone are insufficient, countries around the world are continuously pursuing the development of various antiviral drugs and vaccines.
Research continues on existing antiviral drugs such as oseltamivir, zanamivir, peramivir, and baloxavir, and new treatment strategies are also being developed. Furthermore, research on next-generation vaccines to effectively prevent highly pathogenic H5-type avian influenza is ongoing.
Humans coexist with birds in various environments, such as food production facilities, farms, and zoos. In these settings, avian influenza viruses and avian influenza remain infectious diseases that require ongoing attention and research. The risk should not be underestimated simply because the disease does not spread easily among humans. Even if there are few cases of direct human infection, these diseases can cause enormous social and economic damage requiring the culling of vast numbers of poultry, and the possibility of new risks emerging due to viral mutations cannot be ruled out.
Therefore, we must continuously develop systematic disease control systems, treatment strategies, and preventive measures that enable a rapid response in the event of a viral outbreak. Furthermore, we must conduct ongoing research into the pathological changes the AI virus causes in humans and animals, develop new treatments and vaccines based on these findings, and establish a more systematic national disease control framework. If we correctly recognize the severity of infectious diseases and continue our research and preparedness efforts, we will be able to respond more swiftly and effectively even if new infectious diseases emerge, ensuring that everyone can live in a healthy and safe environment.
