H5N8 is a highly pathogenic avian influenza (HPAI) that primarily affects bird populations, particularly poultry and wild waterfowl, causing severe illness and high mortality. The virus has spread globally, leading to significant outbreaks across various continents.
Understanding H5N8
H5N8 is a subtype of the influenza A virus, categorized by two surface proteins: hemagglutinin (H) and neuraminidase (N). There are 16 H and 9 N subtypes, which combine in various ways, such as H5N1 or H5N8. This virus typically circulates among wild birds, which can carry it asymptomatically. However, when H5N8 infects domestic poultry like chickens, turkeys, and ducks, it causes widespread disease and high mortality. The H5N8 virus originated from the H5N1 virus first detected in China in 1996, and has since evolved and reassorted with other avian influenza viruses.
How H5N8 Spreads
H5N8 primarily spreads through direct contact with infected birds or their droppings, which contain the virus in saliva, mucus, and feces. Contaminated equipment, vehicles, and materials can also facilitate its spread between farms. Wild migratory birds play a significant role in the global dissemination of H5N8, carrying the virus along migration routes and introducing it to new geographical areas. Once introduced, it can spread rapidly within dense poultry populations. Environmental transmission through contaminated water, often from infected wild bird feces, can also lead to infections in domestic poultry.
Implications for Human Health
While H5N8 primarily affects birds, the risk of human infection is considered low. In February 2021, Russia reported seven confirmed H5N8 cases in poultry workers exposed during a farm outbreak. All reported human cases were mild or asymptomatic, with individuals recovering, and there was no evidence of human-to-human transmission.
Despite the low risk, organizations like the World Health Organization continually assess the situation, emphasizing that human infection cannot be entirely ruled out. Symptoms could range from no symptoms to mild illness. In more severe, though rare, cases with other H5 subtypes, symptoms have included fever, aching muscles, headache, cough, shortness of breath, and conjunctivitis, potentially progressing to pneumonia or acute respiratory distress syndrome. Avoiding direct contact with sick or dead birds, their droppings, or contaminated environments remains an important precaution.
Controlling Outbreaks
Controlling H5N8 outbreaks involves a multi-faceted approach focused on limiting its spread, particularly in poultry. Enhanced biosecurity measures are key to preventing the virus’s introduction and spread on farms, including strict access control, disinfection of equipment and vehicles, and preventing contact between domestic poultry and wild birds.
Surveillance programs are important for early detection in wild bird populations and poultry. Rapid diagnosis allows for prompt control measures, often including culling infected flocks to prevent further spread. Movement restrictions on poultry and poultry products are put in place to contain outbreaks. International cooperation and timely reporting are also important for global monitoring and response efforts.