Avian Influenza in Birds
Avian influenza, commonly referred to as bird flu, is a disease caused by the avian influenza Type A virus. It is categorized by disease severity (pathogenicity) in poultry as low pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI) viruses. Workers whose jobs involve contact with infected birds, whether live or dead, or their saliva, nasal secretions, or excrement, are among those at increased risk of exposure to these viruses.
Low Pathogenic Avian Influenza (LPAI) Viruses
Wild, aquatic birds are the natural reservoirs (i.e., hosts) for LPAI viruses worldwide. The virus has been found in over 100 species of birds including seagulls, terns, shorebirds, ducks, swans, and geese. These wild aquatic birds often have respiratory and intestinal infections without showing signs of illness. LPAI viruses can spread easily, generally causing minor illness in domestic poultry, such as chickens, ducks, and turkeys. While up to half of infected chickens can become sick during an outbreak, usually less than 5% of infected chickens die.
Highly Pathogenic Avian Influenza (HPAI) Viruses
Wild birds are also reservoirs for HPAI viruses. In poultry there is concern that LPAI viruses can change into a HPAI virus. These viruses are very contagious and deadly in poultry. They can cause death in 90% to 100% of infected chickens in as little as 48 hours. Wild and domestic ducks typically show no signs of infection while other wild birds may develop serious illness and die.
Avian Influenza in Humans
Avian influenza poses minimal health risk to humans because neither LPAI or HPAI spread easily from infected birds to humans, and there is no evidence of transmission through properly handled and prepared poultry or eggs. However, people have become infected through direct unprotected contact with infected poultry (live or dead) or poultry secretions or excretions (e.g., blood, mucous, or feces), including contaminated surfaces. Direct unprotected contact with infected intermediate hosts, such as pigs, can also pose a risk to humans.
Most cases of avian influenza infection in humans have resulted from direct contact with infected poultry (e.g., domesticated chickens, ducks, and turkeys) or contact with surfaces contaminated with saliva, mucus, or feces from infected poultry. Direct exposure happens when virus particles in aerosolized droplets or dust are inhaled or contact a person’s mucous membranes, such as their eyes, nose, or mouth. Exposure can also occur when a person touches a contaminated surface, object, or material and then touches the mouth, nose, or eyes. The length of time that avian influenza viruses can survive on surfaces varies by the surface type and environmental factors such as temperature and humidity. They can survive longer under cold and wet conditions (weeks to months) than under warm, dry conditions (hours to days). Therefore, routine cleaning and disinfection is recommended in areas that may become contaminated with infectious particles. While uncommon, cases of human-to-human transmission have occurred. Most of these cases have involved unprotected, close, and prolonged contact between a sick patient and a caregiver.
Symptoms in Humans
Although avian influenza usually does not infect humans, there have been rare cases of human infection with these viruses. Most human cases are caused by H7N9 and H5N1 strains of avian influenza viruses. The type of virus (LPAI or HPAI) does not appear to be related to the severity of illness in humans. The signs and symptoms range from asymptomatic or mild illness (e.g. eye redness or mild upper respiratory symptoms) to severe (e.g. pneumonia), requiring hospitalization. Symptoms may include fever or feeling feverish, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, and shortness of breath. Less common symptoms include diarrhea, nausea, vomiting or seizures. Fever may not always be present.
Avian Influenza Outbreaks
Sporadic outbreaks of avian influenza are periodically reported within the United States in commercial poultry flocks, including an HPAI outbreak in West and Midwest states in 2014-2015. In 2022, reports of HPAI virus outbreaks have been reported in commercial poultry farms across multiple U.S. states. Information on the current avian influenza situation can be obtained from the Centers for Disease Control and Prevention (CDC).