Avian influenza, often called bird flu, refers to a group of influenza viruses that naturally circulate among wild aquatic birds. These viruses can infect domestic poultry and other bird species, and in some instances, mammals, including humans.
Understanding Avian Influenza Strains
Avian influenza viruses are classified based on two surface proteins: hemagglutinin (H) and neuraminidase (N). There are 18 known H subtypes and 11 N subtypes, leading to many possible combinations, such as H5N1 or H7N9.
Avian influenza viruses are also categorized by their ability to cause disease in poultry, distinguishing between highly pathogenic avian influenza (HPAI) and low pathogenic avian influenza (LPAI). HPAI viruses cause severe illness and high mortality rates in infected poultry flocks. In contrast, LPAI viruses cause mild or no signs of illness in birds.
How Avian Influenza Spreads
Avian influenza spreads among birds through direct contact with infected birds or their bodily fluids, such as saliva, nasal secretions, and feces. Contaminated environments, including water, feed, equipment, and clothing, also serve as pathways for transmission. Wild migratory birds play a role in disseminating the virus over long distances, often carrying the virus without showing symptoms.
Transmission from birds to humans is rare and occurs through close, prolonged contact with infected birds or heavily contaminated environments. This can involve handling sick or dead poultry or being exposed to their droppings. Human-to-human transmission is even rarer and has not led to sustained spread.
Impact on Animals and Humans
Avian influenza can affect birds, particularly domestic poultry. Infected birds may exhibit respiratory distress, including coughing and sneezing, or neurological signs such as tremors and incoordination. Sudden, unexplained deaths within a flock are also a common outcome, especially with HPAI strains, leading to economic losses for poultry farms due to mortality and culling.
In humans, the symptoms of avian influenza can range from mild, flu-like illness, including fever and muscle aches, to severe respiratory disease. Complications can include pneumonia, acute respiratory distress syndrome, and even death. The severity of illness in humans depends on factors such as the specific viral strain involved, the amount of virus exposure, and the individual’s immune response.
Prevention and Public Health Measures
Preventing avian influenza outbreaks in poultry involves implementing biosecurity measures on farms to limit contact between domestic birds and wild birds. This includes securing poultry houses, restricting visitor access, and disinfecting equipment. Surveillance programs are also in place to monitor wild bird populations and poultry farms for early detection of the virus.
When an outbreak occurs, culling infected flocks helps to contain the spread of the virus and minimize economic impact. Vaccines for poultry are available for specific strains and can be used in some regions as part of a control strategy. For human protection, public health advice includes avoiding contact with sick or dead birds and ensuring proper handling and thorough cooking of poultry and eggs. Monitoring for potential human cases, especially among those with high-risk exposures, remains a priority for public health agencies.