Birds, just like people, get the flu. Bird flu viruses infect birds, including chickens, other poultry, and wild birds such as ducks. Usually bird flu viruses only infect other birds. It is rare for people to get infected with bird flu viruses, but it can happen. Two types, H5N1 and H7N9, have infected some people during outbreaks in Asia, Africa, the Pacific, the Middle East, and parts of Europe. There have also been some rare cases of other types of bird flu affecting people in the United States.

Most of the people who get bird flu have had close contact with infected birds or with surfaces that have been contaminated by the birds' saliva, mucous, or droppings. It is also possible to get it by breathing in droplets or dust that contain the virus. Rarely, the virus has spread from one person to another. It may also be possible to catch bird flu by eating poultry or eggs that are not well cooked.

Bird flu illness in people can range from mild to severe. Often, the symptoms are similar to the seasonal flu, such as

• Fever
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle or body aches
• Fatigue
• Headaches
• Eye redness (or conjunctivitis)
• Difficulty breathing

In some cases, bird flu can cause serious complications and death. As with seasonal flu, some people are at higher risk for serious illness. They include pregnant women, people with weakened immune systems, and seniors aged 65 and older.

Treatment with antiviral medicines may make the illness less severe. They may also help prevent the flu in people who were exposed to it. There is currently no vaccine available to the public. The government does have a supply of a vaccine for one type of H5N1 bird flu virus and could distribute it if there was an outbreak that spread easily from person to person.

There are four types of influenza (flu) viruses: A, B, C and D. Wild aquatic birds, including gulls, terns, and shorebirds, and wild waterfowl, such as ducks, geese and swans are considered reservoirs (hosts) for avian influenza A viruses.

Subtypes of Influenza A Viruses

Influenza A viruses are divided into subtypes on the basis of two proteins on the surface of the virus: hemagglutinin (HA) and neuraminidase (NA). There are 18 known HA subtypes and 11 known NA subtypes. In birds, 16 HA and 9 NA subtypes have been identified. (Two additional subtypes, H17N10 and H18N11, have been identified in bats.) Many different combinations of HA and NA proteins are possible. For example, an “A(H7N2) virus” designates an influenza A virus subtype that has an HA 7 protein and an NA 2 protein. Similarly, an “A(H5N1)” virus has an HA 5 protein and an NA 1 protein.

All known subtypes of influenza A viruses can infect birds, except subtypes A(H17N10) and A(H18N11), which have only been found in bats. Only two influenza A virus subtypes A(H1N1)pdm09, and A(H3N2), are currently circulating among people. Influenza A viruses have been detected and are known to circulate in seven different animal species or groups, including humans, wild water birds, domestic poultry, swine, horses, dogs and bats. In many other animal species, avian influenza A viruses have been reported to cause occasional infections, but do not regularly spread among them (e.g., cats and seals). Equine (horse) influenza A(H3N8) virus routinely circulates and can cause illness in horses, and canine (dog) influenza A(H3N2) virus routinely circulates and can cause illness in dogs.

Lineages of Influenza A Viruses

Avian influenza A viruses that infect birds have evolved into distinct genetic lineages based on the geographic locations where they were first detected. These different lineages can be distinguished by studying the genetic make-up of these viruses. For example, avian influenza A viruses that were first detected in birds in Asia can be recognized as genetically different from avian influenza A viruses that were first detected among birds in North America. These broad lineage classifications can be further narrowed by genetic comparisons that allow researchers to group the most closely related viruses together. The host, time period and geographical location are often used in the lineage name to help further delineate one lineage from another.

Highly Pathogenic and Low Pathogenic Avian Influenza A Viruses

Avian influenza A viruses are classified into the following two categories: low pathogenicity avian influenza (LPAI) A viruses, and highly pathogenic avian influenza (HPAI) A viruses. The categories refer to molecular characteristics of a virus and the virus’ ability to cause disease and mortality in chickens in a laboratory setting. HPAI and LPAI are defined and explained below:

• Low Pathogenic Avian Influenza (LPAI):  Low pathogenic avian influenza viruses cause either no signs of disease or mild disease in chickens/poultry (such as ruffled feathers and a drop in egg production). Most avian influenza A viruses are low pathogenic and cause few signs of disease in infected wild birds. In poultry, some low-pathogenic viruses can mutate into highly pathogenic avian influenza viruses.
• Highly Pathogenic Avian Influenza (HPAI):  Highly pathogenic avian influenza viruses cause severe disease and high mortality in infected poultry. Only some avian influenza A(H5) and A(H7) viruses are classified as HPAI A viruses, while most A(H5) and A(H7) viruses circulating among birds are LPAI A viruses. HPAI A(H5) or A(H7) virus infections can cause disease that affects multiple internal organs with mortality up to 90% to 100% in chickens, often within 48 hours. However, ducks can be infected without any signs of illness. HPAI A(H5) and A(H7) virus infections in poultry also can spill back into wild birds, resulting in further geographic spread of the virus as those birds migrate. While some wild bird species can be infected with some HPAI A(H5) or A(H7) virus subtypes without appearing sick, other HPAI A(H5) and A(H7) virus subtypes can cause severe disease and mortality in some infected wild birds as well as in infected poultry.

Both HPAI and LPAI viruses can spread rapidly through poultry flocks. HPAI and LPAI designations do not refer to or correlate with the severity of illness in cases of human infection with these viruses; both LPAI and HPAI A viruses have caused mild to severe illness in infected humans. There are genetic and antigenic differences between the influenza A virus subtypes that typically infect only birds and those that can infect birds and people.

Avian influenza A viruses rarely infect people. Five subtypes of avian influenza A viruses are known to have caused human infections (H5, H6, H7, H9, and H10 viruses). The most frequently identified subtypes of avian influenza A viruses that have caused human infections are H5, H7 and H9 viruses. Specifically, A(H5N1) and A(H7N9) viruses have caused the majority of avian influenza A virus infections reported in people, with HPAI A(H5N6) and LPAI A(H9N2) viruses also causing human infections in recent years. Human infections with other subtypes, such as A(H6N1), A(H10N3), A(H10N7), and A(H10N8), have been detected in small numbers of people. In the United States, no HPAI A(H7) virus infections have ever been reported in people; however, there have been four laboratory-confirmed cases of LPAI A(H7N2) virus infection in people.

Avian Influenza A(H5) Viruses

There are nine known subtypes of A(H5) viruses [A(H5N1), A(H5N2), A(H5N3), A(H5N4), A(H5N5), A(H5N6), A(H5N7), A(H5N8), and A(H5N9)]. Most A(H5) viruses identified worldwide in wild birds and poultry are LPAI, but occasionally HPAI A(H5) viruses have been detected. Sporadic A(H5) virus infections of humans have occurred, such as with HPAI A(H5N1) viruses associated with poultry outbreaks in many countries. Human infections with HPAI A(H5N1) virus have been reported in 19 countries since 2003, resulting in severe pneumonia and death in more than 50% of cases. Human infections with HPAI A(H5N6) virus have been reported since 2014 from two countries with death occurring in more than 40% of cases, and human infections with HPAI A(H5N8) virus were reported from one country in 2021.

Avian Influenza A(H6) Viruses

LPAI A(H6) virus outbreaks in birds are not internationally reportable, therefore, its true prevalence is unknown. However, LPAI A(H6) viruses have been identified in various species of wild waterfowl and domestic poultry in Eurasia and the Americas. Known subtypes of A(H6) viruses include LPAI A(H6N1) and A(H6N2). In 2013, Taiwan reported the first known human infection with LPAI A(H6N1) virus.

Avian Influenza A(H7) Viruses

There are nine known subtypes of A(H7) viruses A(H7N1), A(H7N2), A(H7N3), A(H7N4), A(H7N5), A(H7N6), A(H7N7), A(H7N8), and A(H7N9)]. Most A(H7) viruses identified worldwide in wild birds and poultry are LPAI viruses. Avian influenza A(H7) virus infection of humans have occurred sporadically. The most frequently identified A(H7) viruses associated with human infections are avian influenza A(H7N9) viruses, which were first detected in China in 2013. While human infections with A(H7N9) viruses are uncommon, they have resulted in severe respiratory illness and death in approximately 40% of reported cases. In addition to A(H7N9) viruses, human infections with A(H7N2), A(H7N3), A(H7N4), and A(H7N7) viruses have been reported and have primarily caused mild to moderate illness with symptoms that included conjunctivitis and/or upper respiratory tract symptoms.

Avian Influenza A(H9) Viruses

There are nine known subtypes of A(H9) viruses A(H9N1), A(H9N2), A(H9N3), A(H9N4), A(H9N5), A(H9N6), A(H9N7), A(H9N8), and A(H9N9)]; all A(H9) viruses identified worldwide in wild birds and poultry are LPAI viruses. A(H9N2) virus has been detected in bird populations in Asia, Europe, the Middle East and Africa. Sporadic avian influenza A(H9N2) virus infections have been reported in people with mild upper respiratory tract illness, although some infections have resulted in death.

Avian Influenza A(H10) Viruses

Known subtypes of A(H10) viruses include A(H10N3), A(H10N4), A(H10N5), A(H10N6), A(H10N7) and A(H10N8). A(H10N4) was found in a mink in 1984 and A(H10N5) was found in swine (pigs) in 2008. The A(H10) virus subtypes known to have caused human infections include A(H10N3), A(H10N7), and A(H10N8). Egypt reported the first human infections with A(H10N7) virus in 2004, while Australia reported human infections with A(H10N7) virus in March 2010. The first human infections with A(H10N8) virus were reported in China in December 2013. The first human A(H10N3) virus infection was reported in China in June 2021. Most A(H10) virus infections in people have resulted from exposure to infected poultry.

Although avian (bird) influenza (flu) A viruses usually do not infect people, there have been some rare cases of human infection with these viruses. Illness in humans from bird flu virus infections have ranged in severity from no symptoms or mild illness to severe disease that resulted in death. Asian lineage H7N9 and highly pathogenic avian influenza Asian lineage H5N1 viruses have been responsible for most human illness from bird flu viruses worldwide to date, including the most serious illnesses and illness with the highest mortality.

Infected birds shed bird flu virus through their saliva, mucous and feces. Human infections with bird flu viruses can happen when virus gets into a person’s eyes, nose or mouth, or is inhaled. This can happen when virus is in the air (in droplets or possibly dust) and a person breathes it in, or possibly when a person touches something that has virus on it then touches their mouth, eyes or nose. Human infections with bird flu viruses have occurred most often after unprotected contact with infected birds or surfaces contaminated with bird flu viruses. However, some infections have been identified where direct contact with infected birds or their environment was not known to have occurred.

The spread of bird flu viruses from one infected person to a close contact is very rare, and when it has happened, it has only spread to a few people. However, because of the possibility that bird flu viruses could change and gain the ability to spread easily between people, monitoring for human infection and person-to-person spread is extremely important for public health.

Signs and Symptoms of Avian Influenza A Virus Infections in Humans

The reported signs and symptoms of bird flu virus infections in humans have ranged from no symptoms or mild illness [such as eye redness (conjunctivitis) or mild flu-like upper respiratory symptoms], to severe (such as pneumonia requiring hospitalization) and included fever (temperature of 100ºF [37.8ºC] or greater) or feeling feverish*, cough, sore throat, runny or stuff nose, muscle or body aches, headaches, fatigue, and shortness of breath or difficulty breathing. Less common signs and symptoms include diarrhea, nausea, vomiting, or seizures.

*Fever may not always be present

Detecting Bird Flu Avian Influenza A Virus Infection in Humans

Bird flu virus infection in people cannot be diagnosed by clinical signs and symptoms alone; laboratory testing is needed. Bird flu virus infection is usually diagnosed by collecting a swab from the upper respiratory tract (nose or throat) of the sick person. Testing is more accurate when the swab is collected during the first few days of illness.

For critically ill patients, collection and testing of lower respiratory tract specimens also may lead to diagnosis of bird flu virus infection. However, for some patients who are no longer very sick or who have fully recovered, it may be difficult to detect bird flu virus in a specimen.

Avian Influenza (AI) type A viruses are divided into subtypes based on two proteins on the surface of the virus:

• Hemagglutinin (HA), of which there are 16 subtypes (H1-H16)
• Neuraminidase (NA), of which there are 9 subtypes (N1-N9)
• Many combinations of HA and NA proteins are possible (i.e., H5N1, H5N2, H7N2, H7N8, etc).

AI viruses are also classified into two groups based on their ability to produce disease in chickens: highly pathogenic avian influenza (HPAI) or low pathogenic avian influenza (LPAI).

• HPAI viruses cause high mortality in poultry and occasionally high death rates in certain species of wild birds.
• LPAI viruses can cause a variety of outcomes in poultry ranging from no apparent clinical signs to moderate death rates. LPAI viruses usually cause little to no signs in wild birds.

H5 and H7 LPAI viruses have the potential to mutate or evolve into HPAI viruses and are closely monitored by animal health officials.

Influenza A viruses are endemic (can infect and regularly transmit) in 6 animal species or groups (wild waterfowl, domestic poultry, swine, horses, dogs, and bats) in addition to humans. Influenza A virus subtypes currently endemic in humans are H3N2 and H1N1 viruses. Examples of different influenza A virus subtypes currently endemic in animals include H1N1 and H3N2 in pigs (different strains than those found in humans), H3N8 in horses, H3N2 in dogs, and H5N1 in wild water birds and domestic poultry.

Influenza A viruses that typically are endemic in one animal species sometimes can cause illness in another species. For example, until 1998, only H1N1 viruses circulated widely in the U.S. pig population. However, in 1998, H3N2 viruses from humans were introduced into the pig population and caused widespread disease among pigs. More recently, H5N1 viruses from birds have caused sporadic infections in wild foxes in the U.S. and in other countries.

Avian influenza A (bird flu) viruses may be transmitted from infected birds to other animals, and potentially to humans, in two main ways:

• Directly from infected birds or from avian influenza A virus-contaminated environments.
• Through an intermediate host, such as another animal.

Direct infection can occur from exposure to saliva, mucous, or feces from infected birds. Bird flu infections among people are rare; however, human infections can happen when enough virus gets into a person’s eyes, nose, or mouth, or is inhaled. People with close or prolonged unprotected contact (not wearing respiratory and eye protection) with infected birds or places that sick birds or their mucous, saliva, or feces have contaminated, might be at greater risk of bird flu virus infection.

Infection through an intermediate host is not as straightforward or as likely to occur, although it is possible. Influenza A viruses have eight separate gene segments. The segmented genome allows influenza A viruses from different species to mix genes (reassortment) and create a new virus if influenza A viruses from two different species infect the same person or animal at the same time.

One possible way that virus reassortment could occur is if a pig were infected with a human influenza A virus and an avian influenza A virus at the same time, the new replicating viruses could reassort and produce a new influenza A virus that had some genes from the human virus and some genes from the avian virus. The resulting new virus might then be able to infect humans and spread easily from person to person, but it could have surface proteins (hemagglutinin and/or neuraminidase) different than those currently found in influenza viruses that routinely circulate in humans—this could make it seem like a “new” influenza virus to people, one that had not been encountered before.

This type of major change in the influenza A viruses is known as “antigenic shift.” Antigenic shift results when a new influenza A virus subtype against which most people have little or no immune protection infects humans. If this new influenza A virus causes illness in people and is transmitted easily from person to person in a sustained manner, an influenza pandemic can occur.

While a “shift” of this kind has not occurred in relation to avian influenza viruses, such a “shift” occurred in the spring of 2009 when an H1N1 virus with genes from North American Swine, Eurasian Swine, humans and birds emerged to infect people and quickly spread, causing a pandemic. When shifts happen, most people have little or no immunity against the new virus.

It is also possible that the process of genetic reassortment could occur in a person who is co-infected with an avian influenza A virus and a human influenza A virus. The genetic information in these viruses could reassort to create a new influenza A virus with a hemagglutinin and/or neuraminidase gene from the avian virus and other genes from the human virus. Influenza A viruses with a hemagglutinin against which humans have little or no immunity that have reassorted with a human influenza virus are more likely to result in sustained human-to-human transmission and have pandemic potential. Therefore, careful evaluation of influenza A viruses recovered from humans and animals that are infected with avian influenza A viruses is important to identify genetic reassortment if it occurs.

Although it is unusual for people to get influenza A virus infections directly from animals, sporadic human infections and outbreaks caused by certain avian influenza A viruses and swine influenza A viruses have been reported.

Avian influenza (“bird flu”) viruses rarely infect people. Most previous bird flu virus infections in people have occurred following close, prolonged, and unprotected (e.g., no gloves or medical mask) contact with infected birds or environments contaminated by their saliva, mucous or poop. For any one person, the risk of infection depends on exposure and specifically on how close and how long the exposure is. Even when people have been infected with bird flu viruses there has very rarely been onward spread from one infected person to another person. Detailed public health investigations are used to determine whether person-to-person spread of bird flu virus has occurred. Below are a few examples of this happening in other countries, however, when it has happened, it has not led to sustained (ongoing) spread among people.

Examples of likely person-to-person spread of bird flu:

• In 1997, the first human infections with H5N1 bird flu viruses were identified in Hong Kong.
• Buxton Bridges C. et al. “Risk of influenza A(H5N1) infection among health care workers exposed to patients with influenza A(H5N1), Hong Kong;”
• Katz JM et al. “Antibody response in individuals infected with avian influenza A(H5N1) viruses and detection of anti-H5 antibody among household and social contacts.”)

• In 2003, in the Netherlands, there was evidence of probable spread of H7N7 virus from two poultry workers to three family members. All three family members had conjunctivitis (pink eye) and one also had influenza (flu)-like illness.
  • (M Du Ry van Beest Holle, Meijer, et al, 2005. “Human to Human Transmission of Avian Influenza /H7N7, The Netherlands, 2003.”)
• In 2004, in Thailand, there was evidence of probable person-to-person spread of H5N1 bird flu virus in a family. Spread of H5N1 bird flu was associated with prolonged, very close unprotected contact between an ill child with H5N1 virus infection and her mother and aunt while the child was hospitalized. Further spread did not occur.
  • (Ungchusak et al, 2005. “Probable Person-to-Person Transmission of Avian Influenza A(H5N1).”)
• In 2005, in Indonesia, limited, non-sustained person-to-person spread of H5N1 bird flu virus could not be excluded among two groups of patients who had no known contact with poultry or other animals.
  • (Kandun et al, 2006. “Three Indonesian Clusters of H5N1 Virus Infection in 2005.”)
• In 2006, in Indonesia, limited, non-sustained person-to-person spread of H5N1 bird flu virus may have occurred among a family cluster of eight probable or confirmed H5N1 cases.
  • (Avian influenza – situation in Indonesia – update 16)
• In December 2007, in China, limited, non-sustained H5N1 bird flu virus spread likely occurred between a sick son and his father through prolonged very close unprotected exposure while the son was in the hospital.
  • (Wang et al, 2008. “Probable limited person-to-person transmission of highly pathogenic avian influenza A(H5N1) virus in China.”)
• Also in 2007, in Pakistan, limited, non-sustained person-to-person H5N1 virus spread likely occurred among brothers.
  • (WHO, Weekly Epidemiological Record, 2008. Human cases of avian influenza A(H5N1) in North-West Frontier Province, Pakistan, October–November 2007
• In 2013, person-to-person infections with (H7N9) bird flu virus were first reported in China. Yearly epidemics of person-to-person infections with H7N9 bird flu viruses in China driven mostly by contact with infected poultry at live poultry markets were reported for a number of years. A small percentage of reported cases were associated with possible limited, non-sustained person-to-person spread, mostly occurring in households between family members. However, limited, non-sustained spread of H7N9 bird flu has been reported in a few cases in hospitals.
  • (Xiang, N et al, 2016.”Assessing Change in Avian Influenza A(H7N9) Virus Infections During the Fourth Epidemic — China, September 2015–August 2016“;
  • Chen et al. 2016. “Nosocomial Co-Transmission of Avian Influenza A(H7N9) and A(H1N1)pdm09 Viruses between 2 Patients with Hematologic Disorders;”
  • Fang et al, 2015. “Nosocomial transmission of avian influenza A(H7N9) virus in China: epidemiological investigation.”

Person-to-person spread of other non-human (animal-origin) flu Type A viruses can range from occasional, limited, and non-sustained spread of one or more generations without further spread (“dead-end transmission”), to efficient and sustained person-to-person spread. Easy and sustained (ongoing) spread of non-human flu Type A viruses (including bird flu viruses) among people in the community is needed for a flu pandemic to begin.

Human infections with avian influenza A viruses are uncommon but have occurred sporadically in many countries, usually after unprotected exposures (e.g. not using respiratory or eye protection) to infected poultry or virus-contaminated environments and have resulted in mild-to-severe illness with a wide range of symptoms and complications. A small number of human infections with avian influenza A viruses have been attributed to exposure to infected wild birds. For some human infections, the source of the virus infection was not determined. Human infections have occurred with different subtypes of low pathogenic and highly pathogenic avian influenza A viruses. The designation of “low” versus “highly” pathogenic avian influenza A virus refers to specific criteria, including mortality in experimentally infected poultry, and not to the severity of illness with human infections. Clinical illness associated with human infections with avian influenza A viruses does not necessarily correlate with virus pathogenicity in infected birds.

Low Pathogenic Avian Influenza A Virus Infections*

Subtypes of low pathogenic avian influenza (LPAI) A viruses that have been virologically confirmed to have infected people include A(H6), A(H7), A(H9), and A(H10) viruses.

A(H6) Virus Infections

• LPAI A(H6N1) virus infection was reported in one person with moderate lower respiratory tract disease in Taiwan in 2013.

A(H7) Virus Infections

• LPAI A(H7N2) virus infection was reported in a small number of people with conjunctivitis (pink eye), mild upper respiratory tract symptoms, or lower respiratory tract disease in the U.K. and U.S. since 2002. Four infections have been identified in the U.S. since 2002, including 2 that resulted from cat-to-human transmission of an LPAI A(H7N2) virus circulating among cats in 2016.
• LPAI A(H7N3) virus infection was reported in a small number of people with conjunctivitis or mild upper respiratory tract symptoms in the U.K. and Canada since 2004.
• LPAI A(H7N4) virus infection was reported in one person with pneumonia in China in 2017.
• LPAI A(H7N7) virus infection was reported in one person with conjunctivitis in the U.K. in 1996.
• LPAI A(H7N9) virus infection was reported in more than 1500 people in China, particularly during epidemics from 2013-2017, including cases exported to Hong Kong, Macau, Malaysia, Taiwan, and Canada. Clinical syndromes have included mild upper respiratory tract symptoms, lower respiratory tract disease, encephalitis, severe pneumonia with respiratory failure, and multi-organ failure. The case fatality proportion in hospitalized patients is approximately 40%. A very small number of people were reported with asymptomatic infection after investigations in China during 2013.

A(H9) Virus Infections

• LPAI A(H9N2) virus infections have been reported sporadically in more than 80 people since 1998 in China, and in Hong Kong, Bangladesh, Cambodia, Egypt, India, Oman, Pakistan, and Senegal. Most cases have been in children and have resulted in mild upper respiratory tract illness symptoms, but lower respiratory tract disease including severe pneumonia, and respiratory failure, including a small number of deaths, have been reported.

A(H10) Virus Infections

• LPAI A(H10N3) virus infection was reported in one person with severe pneumonia and respiratory failure in China in 2021.
• LPAI A(H10N7) virus infection was reported in a small number of people with conjunctivitis or mild upper respiratory tract symptoms in Egypt in 2004 and Australia in 2010.
• LPAI A(H10N8) virus infection was reported in a small number of people with severe pneumonia with respiratory failure, including a few deaths, in China since 2013.

Highly Pathogenic Avian Influenza A Virus Infections*

Subtypes of highly pathogenic avian influenza (HPAI) A viruses that have been virologically confirmed to have infected people include A(H5) and A(H7) viruses.

A(H5) Virus Infections

• HPAI A(H5N1) virus infections have been reported in more than 880 people with approximately 50% case fatality proportion since 1997, including 20 cases and 7 deaths in Hong Kong during 1997-2003, and more than 860 cases reported in 19 countries since November 2003. Mild upper respiratory tract symptoms, lower respiratory tract disease, severe pneumonia with respiratory failure, encephalitis, and multi-organ failure have been reported. One case of asymptomatic infection was reported in Vietnam in 2011, one of case of asymptomatic infection was reported in the U.K. in 2021 and one case was reported in the United States in 2022.
• HPAI A(H5N6) virus infections have been reported in more than 60 people in China since 2014 and one case was reported in Laos in 2021. Mild upper respiratory tract symptoms, lower respiratory tract disease, severe pneumonia with respiratory failure, and multi-organ failure have been reported. Case fatality proportion in hospitalized patients is >40%.
• HPAI A(H5N8) virus infections were reported in a small number of asymptomatic people in Russia in 2020.

A(H7) Virus Infections

• HPAI A(H7N3) virus infections have been reported in a small number of people with conjunctivitis since 2004 in Canada and in other countries.
• HPAI A(H7N7) virus infections have been reported in more than 90 people, since the first human infection was identified in the U.S. in 1959; although that infection was associated with hepatitis, most infections have been associated with conjunctivitis. However, mild upper respiratory tract symptoms, lower respiratory tract disease, severe pneumonia with respiratory failure, and multi-organ failure have been reported, including one death. Most reported cases were associated with exposures during widespread poultry outbreaks in the Netherlands in 2003.
• HPAI A(H7N9) virus infections have been reported in China since 2016, including lower respiratory tract disease, severe pneumonia with respiratory failure, and multi-organ failure. The case fatality proportion in hospitalized patients is >40%.

Human-to-Human Transmission of Avian Influenza A Viruses

Human-to-human transmission of avian influenza A viruses is rare. Probable limited, non-sustained, human-to-human transmission has been reported in a small number of people without poultry exposures who had close unprotected exposure to a symptomatic index case of HPAI A(H5N1) virus infection, HPAI A(H7N7) virus infection, or LPAI A(H7N9) virus infection. Most reported cases of probable limited, non-sustained, human-to-human transmission have occurred among blood-related family members after unprotected, prolonged close household exposure to a symptomatic family member. However, a small number of reported cases occurred after unprotected, prolonged close exposure to a very sick family member in a hospital. A few cases of probable limited, non-sustained, human-to-human transmission in a hospital have been reported among unrelated patients after unprotected exposures.

*Sources: Adapted from Uyeki T and Peiris M. Infectious Disease Clinics of North America 2019; and World Health Organization reports. For the latest summary, case counts of human infections, and risk assessment, see the World Health Organization Influenza at the human-animal interface summary and assessment: https://www.who.int/teams/global-influenza-programme/avian-influenza/monthly-risk-assessment-summary

The signs and symptoms of bird flu virus infections in humans range from no symptoms or mild illness such as eye redness or mild flu-like upper respiratory symptoms to severe illness such as pneumonia requiring hospitalization.

Other symptoms may include:

• fever or feeling feverish
• cough
• sore throat
• runny or stuff nose
• muscle or body aches
• headaches
• fatigue
• shortness of breath or difficulty breathing.

Less common signs and symptoms include diarrhea, nausea, vomiting, or seizures.

You are being given this information and these instructions because you were recently around poultry or wild birds found to be infected with avian influenza viruses (“bird flu” viruses). Viruses like these have caused rare, sporadic infections in people in other countries, resulting in human illness ranging from mild (e.g., eye infections, cough, sore throat) to severe (e.g., pneumonia, shortness of breath, difficulty breathing). These viruses have the potential to cause human illness in people who have been exposed to infected birds.

Infected birds shed bird flu viruses in their saliva, mucous and feces. Human infections with bird flu viruses are rare, but they can happen when virus gets into a person’s eyes, nose, or mouth, or is inhaled. This can happen when virus is in the air (in droplets or possibly dust) and a person breathes it in, or possibly when a person touches something that has virus on it and then touches their mouth, eyes or nose. Most often these infections have occurred after unprotected contact with infected birds.

Because human infections with these bird flu viruses are possible, all people with direct or close exposure to infected well-appearing, sick, or dead birds, infected flocks or contaminated surfaces should be monitored for illness for 10 days after their last exposure. State and local health departments are helping to monitor people’s health and you should contact your health department if you get any of the symptoms listed on this fact sheet during the 10 days after your last exposure. By following the instructions below, you can help ensure that you receive prompt medical evaluation, testing, and appropriate treatment if you become ill with signs and symptoms that could be due to bird flu.

Please follow these instructions carefully:

1. Monitor your health for symptoms of avian influenza virus infection.
During and then immediately after your last exposure to infected birds or contaminated surfaces, monitor yourself daily for any of these signs and symptoms for 10 days:

• Fever (Temperature of 100°F [37.8°C] or greater) or feeling feverish/chills*
• Cough
• Sore throat
• Difficulty breathing/Shortness of breath
• Eye tearing, redness, or irritation
• Headaches
• Runny or stuffy nose
• Muscle or body aches
• Diarrhea

*Fever may not always be present

You should observe your health daily even if you carefully followed all guidelines and instructions for properly putting on and taking off personal protective equipment (PPE) and maintaining biosecurity precautions.

Re-start your 10-day monitoring period from Day 1 if you are around infected birds or contaminated environments again.

Your local/state health department should contact you regarding your exposure. Please follow all additional instructions that are given to you regarding monitoring for symptoms. They may, for example, ask you to respond to a daily phone call, email, or text message with a report on your health status.

2. Call your state/local health department immediately if you develop any illness signs or symptoms during the 10-day observation period.
Your health department will help you determine what to do next.

Remember:

• Most of the signs and symptoms of bird flu overlap with those of other respiratory illnesses (like seasonal flu or COVID-19). Fever may not always be present.
• If you develop any of the signs or symptoms listed on this fact sheet, immediately call the health department of the state you are in at the time. Your health department wants to hear from you, even if it turns out to be a ‘false alarm’. Your health department will give you further instructions and might ask you to get tested for bird flu virus infection.
• If you have symptoms, stay home and limit contact with others as much as possible until the results of your test are known. Your health department might have additional instructions for you as well.
• To test for bird flu virus, a doctor or nurse will collect a sample from you by swabbing your nose and/or throat.
• If you become sick while you are observing your health, a doctor might prescribe an antiviral medication for you that is used for treatment of seasonal influenza. These drugs can also treat bird flu virus infection. It is important to start antiviral treatment as soon as possible and to follow the directions for taking all of the medication that is prescribed. (CDC recommends that clinicians prescribe antiviral medications for treatment of ill persons who had exposure to bird flu viruses and are suspected to be infected with bird flu viruses.)

Here’s an example of a log you can keep as a reminder to check your health each day for illness signs and symptoms.

Antiviral Drugs Can Be Used to Treat Illness

CDC currently recommends treatment as soon as possible with flu antiviral drugs for people who get sick with bird flu. Antiviral treatment works best when started as soon as symptoms begin. If you get sick after being in close contact with sick or potentially infected birds, contact your state or local health department and a health care provider right away. They may have you get tested for bird flu and a health care provider may write you a prescription for an antiviral drug to treat your illness. It’s important to take the medication as directed.

Available data on bird flu viruses spreading worldwide suggest that most bird flu virus infections would respond to treatment with flu antiviral drugs, if treatment is started early after symptoms begin. However, some evidence shows flu antiviral drugs may not work as well against some A(H5N1) and A(H7N9) bird flu viruses that were first detected in Asia. When flu viruses evolve in ways that make antiviral treatment less effective, this is called antiviral resistance. CDC regularly tests bird flu viruses for antiviral resistance.

The U.S. Government is Developing A(H5N1) and A(H7N9) Bird Flu Vaccines in Case they are Needed

The United States federal government maintains a stockpile of vaccines, including vaccines against A(H5N1) and A(H7N9) bird flu viruses. These vaccines could be used if similar viruses were to begin spreading easily from person to person. Since flu viruses change, CDC continues to make candidate vaccine viruses (CVVs) as needed. Creating a CVV is the first step in producing a flu vaccine.

CDC considers the current risk to the general public from the H5N1 bird flu outbreak in wild birds and poultry to be low.

Protective actions around birds

• As a general precaution, whenever possible people should avoid direct contact with wild birds and observe them only from a distance.
• Wild birds can be infected with avian (bird) influenza (flu) A viruses even if they don’t look sick.
• Avoid unprotected contact with domestic birds (poultry) that look sick or have died.
• Do not touch surfaces that may be contaminated with saliva, mucous or feces from wild or domestic birds.

The best prevention is to avoid sources of exposure

The best way to prevent avian (bird) influenza (flu) is to avoid sources of exposure whenever possible. Infected birds shed bird flu virus in their saliva, mucous and feces. People rarely get bird flu; however, human infections with bird flu viruses can happen when enough virus gets into a person’s eyes, nose or mouth, or is inhaled. This can happen when virus is in the air (in droplets or possibly dust) and a person breathes it in, or when a person touches something that has virus on it and then touches their mouth, eyes or nose. Bird flu infections in people happen most often after close, prolonged and unprotected (no gloves or other protective wear) contact with infected birds and then the person touches their mouth, eyes, or nose.

Minimize contact with wild birds or sick or dead poultry by wearing gloves and washing your hands with soap and water after touching birds. If available, wear respiratory protection, such as a medical facemask.

Protective actions for people who come into contact with birds infected with bird flu because of their job

If you must handle sick poultry because of your job as a bird flu outbreak responder, use protective wear (like gloves, a medical facemask, and eye protection), wash your hands with soap and water after touching birds, and change your clothes before contact with healthy domestic poultry and after handling wild birds. Then, throw away the gloves and facemask. CDC has more information available on what to do after you have been exposed to infected poultry.

CDC has information available for if you have had direct contact with infected birds and you become sick.

Information for other groups who may come into contact with birds

Hunters who handle wild birds should dress game birds in the field when possible and practice good biosecurity to prevent any potential disease spread. If possible, wear gloves when dressing birds, and wash hands with soap and water afterwards.

Bird owners should practice good biosecurity and prevent contact between their birds and wild birds. Bird owners should report sick birds or unusual bird deaths to the state or the federal government, either through their state veterinarian or by calling USDA’s toll-free number at 1-866-536-7593. Find additional information on biosecurity for backyard flocks on USDA’s APHIS website.

For more information about bird flu and what to do if you have been exposed to bird flu, visit: What To Know About Bird Flu (cdc.gov) [154 KB, 2 Pages].

If you’ve had direct contact with infected birds and become sick

CDC has information available for different groups of people who may become infected with birds and become sick.

People who become sick within 10 days of their exposure to infected birds should isolate at home away from their household members and should not go to work or school until they are proven not to have bird flu virus infection and have recovered from their illness. The local or state public health department can assist in monitoring and advising when isolation is no longer required.

Close contacts (family members, etc.) of people who have been exposed to bird flu viruses should monitor their health and report to their health care provider any new symptoms, especially respiratory symptoms, within 10 days of the exposure.

CDC also recommends that everyone 6 months and older get a seasonal flu vaccine every year.

It is especially important that people who may have exposure to sick birds get a seasonal flu vaccine, ideally 2 weeks before their potential exposure, if possible. Seasonal flu vaccination will not prevent infection with bird flu viruses, but can reduce the risk of getting sick with human and bird flu viruses at the same time.

What to do if you find a dead bird

State and local governments have different policies for collecting and testing birds, so check with your state health department, state veterinary diagnostic laboratory, or state wildlife agency for information about reporting dead birds in your area. Wildlife agencies regularly investigate sick or dead bird events if large numbers are impacted. This type of reporting could help with the early detection of illnesses like West Nile virus or bird flu. If local authorities tell you to throw away the bird’s carcass (body), don’t touch it with your bare hands. Use gloves or a plastic bag turned inside out to place the body in a garbage bag, which can then be thrown away in your regular trash. To report unusual signs in birds you have seen in the wild, call 1-866-536-7593.

It is safe to eat properly handled and cooked poultry in the United States. The proper handling and cooking of poultry and eggs to an internal temperature of 165 degrees F kills bacteria and viruses, including bird flu viruses.

Preparing food

The U.S. poultry industry has strict health and safety standards, including regular monitoring for bird flu. It is safe to eat properly handled and cooked poultry in the United States. Properly handling and cooking poultry and eggs to an internal temperature of 165˚F kills bacteria and viruses, including bird flu viruses. People should handle raw poultry hygienically and cook all poultry and poultry products (including eggs) all the way before eating. Eating uncooked or undercooked poultry can make you sick. More information is available at Chicken and Food Poisoning.

While there is no evidence that anyone has gotten bird flu after eating properly cooked poultry products, uncooked poultry and poultry products (like blood) could have been the source of a small number of bird flu infections in people in Southeast Asia. Visit USDA – Food Safety Education for instructions on handling poultry safely.

Traveling to other countries

Currently, CDC does not recommend against travel to any countries due to bird flu viruses in wild birds, poultry, or people. CDC recommends that travelers to countries and states with bird flu outbreaks in poultry or people:

• Do not visit poultry farms, bird markets and other places where live poultry are raised, kept, or sold, if possible.
• Do not eat raw or undercooked poultry products and wash your hands after touching uncooked poultry.
• Practice good hygiene and cleanliness.
• Visit a doctor if you become sick during or after travel.

What is avian flu (bird flu)?

Avian influenza, also called bird flu, is caused by a virus that infects birds such as chickens, turkeys, geese, pigeons, and pheasants. The virus is found in an infected bird’s poop as well as fluids from the bird’s eyes, nose, or mouth.

Bird flu doesn’t usually infect people, however, there are a few ways you can get infected. A person can be infected with bird flu if they

• Touch their eyes, nose or mouth after working with infected live or dead birds.
• Touch their eyes, nose, or mouth after visiting places where infected birds have lived.
• Breathe in droplets or dust contaminated with the virus.
• Have close contact with a person already sick with the disease, though this is rare.

Symptoms of bird flu range from mild eye infections to a flu-like illness. In severe cases, bird flu can cause pneumonia and death.

Who can get bird flu?

Most travelers are unlikely to get bird flu. Travelers who work with animals, such as veterinarians, farmers, animal industry experts, and wildlife professionals, or people who visit poultry farms or live-animal markets may be more likely to get infected.

What can travelers do to prevent bird flu?

There is no vaccine to prevent bird flu, but there are steps you can take to protect yourself.

Avoid touching birds and visiting places where birds live

• Do not touch birds whether they are alive or dead.
• Avoid visiting live bird and poultry markets.
• Avoid other markets or farms with animals.

Avoid Germs

• Wash your hands often with soap and water for at least 20 seconds.
• If soap and water aren’t available, clean hands with hand sanitizer containing at least 60% alcohol.
• Don’t touch your eyes, nose, or mouth. If you need to touch your face, make sure your hands are clean.
• Cover your mouth and nose with a tissue or your sleeve (not your hands) when coughing or sneezing.
• Try to avoid close contact, such as kissing, hugging or sharing eating utensils or cups with people who are sick.

Avoid preparing or eating raw or undercooked poultry products

• Eat meat and poultry that is fully cooked (not pink) and served hot.
• Eat hard-cooked eggs (not runny).
• Don’t eat or drink dishes that include blood from any animal.
• Don’t eat food from street vendors.

If you do handle or prepare poultry products or meat, read these 4 Steps to Food Safety to learn how to prepare poultry in a way that won’t make you or others sick.

If you feel sick and think you may have bird flu, particularly if you have a fever, talk to a healthcare provider and tell them about your travel. Stay away from other people while you are sick.

Avian influenza (or bird flu) is a disease of birds caused by infection with avian influenza A viruses. Infected birds shed bird flu virus in their saliva, mucous, and feces. People rarely get bird flu; however, human infections with bird flu viruses can happen if enough virus is inhaled or gets into a person’s mouth, eyes, or nose. Bird flu infections happen most often after someone has close, prolonged and unprotected (no gloves or other personal protective equipment) contact with infected birds and then touches their mouth, eyes, or nose.

Domestic poultry may be infected with highly pathogenic avian influenza (HPAI) A viruses or low pathogenic avian influenza (LPAI) A viruses:

• The highly pathogenic viruses spread quickly and may kill nearly an entire poultry flock within 48 hours.
• The low pathogenic viruses may not cause symptoms or may cause only mild symptoms such as ruffled feathers or a drop in egg production.

The classification of low pathogenic or highly pathogenic avian influenza A virus refers to the ability of the virus to cause disease in chickens in the laboratory, not in humans. Human infection with low pathogenic and highly pathogenic avian influenza A viruses have resulted in a range of symptoms from mild to severe.

Avian influenza A viruses are a public and occupational health concern for several reasons, including:

• Some of these viruses have passed sporadically from poultry to humans and caused serious illness and death.
• They may change into a form that is highly infectious in humans and spreads easily from person to person.
• As these viruses threaten domestic poultry throughout the world, they are also a risk to workers worldwide who have contact with poultry.

Which animals can be infected?

Avian influenza A viruses occur naturally among wild aquatic birds worldwide. Avian influenza viruses have also infected other animals, including ducks, chickens, turkeys, pigs, whales, horses, seals, dogs, and cats. Influenza A viruses that infect one animal species may sometimes cross over and cause illness in another species, including people.

Which workers are at risk?

Avian influenza A viruses usually do not infect humans; however, sporadic cases have been reported. The disease can be transmitted to unprotected workers who have contact with infected wild birds, poultry, or contaminated materials or surfaces.

Examples of poultry workers and other workers at risk include the following:

• Broiler breeder farms, hatcheries, grow-out farms, and processing plant workers
• Layer farm workers
• Turkey farm workers
• Disease control and eradication workers (including Federal, contract, and company workers)
• Live-bird market workers
• Wildlife biologists who handle birds
• Animal welfare and rescue workers who handle infected animals
• Animal control workers who handle infected animals

How do workers become infected?

Infected birds shed bird flu virus in their saliva, mucous, and feces. Human infections with bird flu viruses are rare but can happen if enough virus is inhaled or gets into a worker’s mouth, eyes, or nose. This can happen if virus is in the air and a worker breathes it in, or if a worker touches something that has virus on it and then touches their mouth, eyes or nose. Bird flu infections happen most often after someone has close, prolonged and unprotected (no gloves or other personal protective equipment) contact with infected birds and then touches their mouth, eyes, or nose.

The virus may be transmitted to workers from contact with one of the following:

• Infected wild birds or poultry that are sick or dead
• Droppings of infected birds
• Contaminated litter
• Contaminated materials or surfaces such as egg collection containers

Protective measures should be taken by anyone likely to have exposure to avian influenza A viruses.

What are the symptoms?

The signs and symptoms of bird flu virus infections in humans range from no symptoms or mild illness such as eye redness or mild flu-like upper respiratory symptoms to severe illness such as pneumonia requiring hospitalization.

Other symptoms may include:

• fever or feeling feverish
• cough
• sore throat
• runny or stuff nose
• muscle or body aches
• headaches
• fatigue
• shortness of breath or difficulty breathing.

Less common signs and symptoms include diarrhea, nausea, vomiting, or seizures.

Where are workers at risk?

Avian influenza A viruses are routinely detected in wild birds. Around the world and in North America, avian influenza A outbreaks occur in poultry from time to time. Outbreaks of some avian influenza A viruses in poultry have been associated with illness and death in humans in Asia, Africa, Europe, the Pacific, and the Near East. While very rare, some avian influenza A viruses have caused illness in humans in North America.

What are other potential hazards to responders during an avian influenza outbreak?

Responders to an avian influenza outbreak may be at risk of exposure to additional hazards including:

• Ammonia
• Chemical disinfectants
• Dust
• Formaldehyde
• Heat stress
• Fatigue
• Musculoskeletal injuries
• Stress

Depopulation and disposal processes may have hazards associated with them such as carbon dioxide exposure, heat exposure, and slips on wet surfaces if proper procedures are not followed.