The H3N8 virus is a subtype of the Influenza A virus, commonly found in various animal populations. It circulates naturally in specific species. Understanding its characteristics is important due to its presence in animals and rare human infections.
Understanding H3N8’s Origins
The H3N8 virus originates primarily from wild aquatic birds, its natural reservoir. From these hosts, the virus adapted and spread to other animal species. For example, the H3N8 subtype is the main cause of equine influenza, having created widespread epidemics in horses in the 1960s.
Beyond horses, H3N8 has also been found in dogs, with outbreaks of canine influenza first identified in Florida in 2004. This canine strain is closely related to equine H3N8, suggesting a direct transmission from horses to dogs. The virus was also reported in seals in 2011, showing its ability to adapt to marine mammals.
Human Infections and Transmission
Human infections with the H3N8 avian influenza virus are rare. While not known to infect humans prior to 2022, three cases were reported in China in 2022 and 2023. These infections likely occurred through direct or indirect exposure to infected live poultry or contaminated environments, such as live animal markets.
The World Health Organization (WHO) and other health organizations state that H3N8 does not appear to spread easily from person to person. Studies show human-isolated H3N8 can transmit between ferrets with low efficiency. Public health officials closely monitor these rare human cases and their close contacts for symptoms, but there is no evidence of sustained human-to-human transmission.
Recognizing Symptoms and Staying Safe
Symptoms in rare human cases of H3N8 infection are similar to the flu. These can include fever, cough, sore throat, runny or stuffy nose, muscle aches, headaches, and fatigue. Vomiting and diarrhea may occur, especially in children. Severe pneumonia and acute respiratory distress syndrome have also been reported.
To minimize exposure, good hygiene is important. This includes frequent handwashing with soap and water after handling animals, meat, or eggs. Alcohol-based hand sanitizers are an alternative if soap and water are not available. Avoid direct contact with sick or dead poultry, wild birds, or other sick animals. When contact with potentially infected animals is unavoidable, wear appropriate personal protective equipment.
Global Surveillance and Response
Public health organizations worldwide actively monitor influenza viruses like H3N8 through global surveillance systems. The World Health Organization (WHO) operates the Global Influenza Surveillance and Response System (GISRS), a network of nearly 150 National Influenza Centres performing influenza surveillance. This system helps identify emerging influenza viruses that could potentially cause pandemics.
Collaborative efforts in research and risk assessment are underway to understand novel zoonotic influenza viruses. Organizations like the Centers for Disease Control and Prevention (CDC) conduct research to assess the risk these viruses pose to humans and support the development of prevention and treatment strategies. This includes developing candidate vaccine viruses (CVVs) for pandemic preparedness efforts, though specific H3N8 human vaccines are not widely available. These global monitoring and research initiatives aim to detect changes in viral characteristics, epidemiology, and clinical patterns that could pose a threat to human or animal health.