As the global spread of Bird Flu (highly pathogenic avian influenza (HPAI), specifically H5N1, increases rapidly, public health officials and scientists are closely monitoring the situation to prevent spillovers from birds and animals to humans. This article will discuss the recent global outbreak trends of HPAI, future pandemic threats, and what it means from a public health perspective.
Let’s begin by understanding what Highly Pathogenic Avian Influenza (HPAI) means. HPAI is a subtype of the avian influenza A virus that primarily affects both wild and domestic birds. The H5N1 virus was first identified in domestic waterfowl in Southern China and later caused an outbreak in Hong Kong, resulting in 18 human cases, with 6 deaths. This virus has severe effects on poultry, leading to a high fatality rate and often resulting in the culling of entire farming operations. Although human infections are rare, they carry a 50% mortality rate, making them a significant public health threat.
After a period of lower incidence, HPAI re-emerged and spread across the world, including Africa, the Middle East, and Asia, through wild bird migration networks. Between 2014 and 2016, gene-swapping among H5 viruses led to the emergence of H5N6 and H5N8 subtypes, further diversifying the hemagglutinin (HA) gene. By 2018-2020, these subtypes replaced the original H5N1 strains, becoming globally dominant, with sporadic human cases. In 2021-2023, a new H5N1 virus (clade 2.3.4.4b) emerged with adaptations for wild birds, spreading across Asia, Africa, Europe, and the Americas. By 2022, it caused widespread outbreaks in U.S. poultry and rare human infections, raising concerns about potential mammalian spillover and pandemic risk.
Recent Surge in Bird Flu Cases
Recent increases in bird flu cases have been alarming. Over the past few years, the global spillover and outbreak events of bird flu have significantly risen, threatening global health security, economic stability, and biodiversity worldwide. HPAI can infect a wide range of domestic and wild mammals. Detection of HPAI in domestic and wild birds is not uncommon. It can infect multiple species, including chickens, ducks, quails, turkeys, and guinea pigs. In most cases, avian influenza viruses (both low pathogenic and highly pathogenic) circulate freely among species in the population. Some developing countries report and consider HPAI as an endemic disease of poultry. The United States and Canada, along with other affected countries, have reported recent outbreaks of HPAI. HPAI has severe economic impacts on the poultry industry, as it often leads to culling and farm closures in infected premises.
HPAI has also been detected in domestic animals, including cattle, significantly impacting the U.S. dairy industry. You can find the latest HPAI case detections in livestock here: USDA HPAI Detections.
How Can Humans Get Infected with HPAI?
Although animal-to-human transmission is rare in bird flu cases, there have been incidents where humans were infected. Human infections caused by avian influenza viruses can vary in severity, ranging from asymptomatic or mild cases to severe disease, sometimes resulting in death. Among the avian influenza A viruses, H7N9, highly pathogenic H5N1, and H5N6 have been responsible for most reported human infections worldwide, often leading to severe illness with high mortality rates.
Infected birds shed avian influenza viruses through saliva, mucus, and feces. In some cases, other infected animals may carry the virus in their respiratory secretions, organs, blood, or bodily fluids, including milk.
Human infections occur when the virus enters the eyes, nose, or mouth, or is inhaled. This can happen through:
- Airborne exposure: Virus-laden droplets, aerosols, or dust particles come into contact with mucous membranes.
- Direct contact: A person touches contaminated surfaces and then touches their face, eyes, nose, or mouth.
Due to its ability to spread through multiple pathways, avian influenza remains a serious global health concern, requiring strict surveillance and biosecurity measures to prevent transmission.
Is H5N1 a Pandemic Threat?
The primary concern surrounding H5N1 is its potential for human-to-human transmission. Currently, H5N1 does not spread efficiently among humans. However, virologists warn that:
- Genetic mutations or reassortment with human influenza viruses could enable efficient human transmission.
- Increased mammalian infections provide opportunities for viral adaptation.
- The human population has limited immunity, making this pathogen high-risk if it overcomes transmission barriers
The World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) closely monitor genetic changes in circulating H5N1 strains to detect signs of human adaptation.
The recent surge in H5N1 cases underscores the urgent need for global surveillance, biosecurity measures, and pandemic preparedness. While the virus has not yet achieved sustained human-to-human transmission, its continued evolution and spillover events into mammals warrant vigilant monitoring and proactive mitigation efforts. Strengthening One Health approaches that integrate human, animal, and environmental health will be critical in preventing future outbreaks and potential pandemics.
