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Although avian influenza A viruses usually do not infect humans, rare cases of human infection with avian influenza A viruses have been reported. Most human infections with avian influenza A viruses have occurred following direct contact with infected poultry. Human illness from infection with avian influenza A viruses has ranged from eye infections (conjunctivitis) to severe respiratory disease (pneumonia) to death.
Since November 2003, nearly 600 sporadic cases of human infection with highly pathogenic avian influenza A (H5N1) virus (referred to as HPAI H5N1 or H5N1) have been reported by 15 countries in Asia, Africa, the Pacific, Europe and the Near East. HPAI H5N1 viruses have never been detected among wild birds, domestic poultry, or people in the United States. However, an outbreak caused by another subtype, highly pathogenic avian influenza A (H5N2), was reported in Texas in 2004. This was the first outbreak of highly pathogenic avian influenza among poultry in the United States in 20 years. The outbreak was reported in a flock of 7,000 chickens in south-central Texas. No transmission of highly pathogenic avian influenza A(H5N2) virus to humans was reported.
The World Health Organization (WHO) maintains situation updates and cumulative reports of human cases of avian influenza A (H5N1) [26 KB, 1 page]. Most human cases of H5N1 virus infection are thought to have occurred as a result of direct or close contact with sick or dead infected poultry.
Other subtypes of avian influenza A viruses also have infected humans, including low pathogenic avian influenza A (LPAI) viruses and highly pathogenic avian influenza A (HPAI) viruses. Public health authorities closely monitor cases of human illness associated with avian influenza A virus infections because of concerns about the potential for more widespread infections and transmission in humans. The spread of avian influenza A viruses from one ill person to another through prolonged, unprotected, close contact has been reported very rarely, and has been limited, inefficient and not sustained. However, because avian influenza A viruses have the potential to change and gain the ability to spread easily between people, monitoring for human infection and person-to-person transmission is extremely important for public health.
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Signs and Symptoms of Avian Influenza A Virus Infections in Humans
The reported signs and symptoms of avian influenza A virus infections in humans have ranged from eye infections (conjunctivitis) to influenza-like illness symptoms (e.g., fever, cough, sore throat, muscle aches) to severe respiratory illness (e.g. shortness of breath, difficulty breathing, pneumonia, acute respiratory distress, viral pneumonia) with multi-organ disease, sometimes accompanied by nausea, abdominal pain, diarrhea, vomiting and sometimes neurologic changes (altered mental status, seizures).
Detecting Avian Influenza A Virus Infection in Humans
Avian influenza A virus infection of humans cannot be diagnosed by clinical signs and symptoms alone, so laboratory testing is required. Avian influenza A virus infection is usually diagnosed by collecting a swab from the nose or throat during the first few days of illness. This specimen is sent to a laboratory, where they will either look for avian influenza A virus using a molecular test or they will try to grow the virus, or both. Growing avian influenza A viruses should only be done in laboratories with high levels of protection. If it is late in the illness, unless the person is critically ill, it may be difficult to find an avian influenza A virus directly using these methods. Sometimes it may still be possible to diagnose avian influenza A virus infection by looking for evidence of the body's response to the virus infection by detecting antibodies to the virus. This is not always an option because it requires two blood specimens (one taken during the first few days of illness and another taken some weeks later) and it can take several weeks to verify the results, and testing must be performed in a special laboratory, such as at CDC.
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Treating Avian Influenza A Virus Infections in Humans
CDC and WHO currently recommend oseltamivir, a prescription antiviral medication, for treatment and prevention of human infection with avian influenza A viruses. Analyses of available H5N1 viruses circulating worldwide suggest that most viruses are susceptible to oseltamivir. However, some evidence of resistance to oseltamivir has been reported in H5N1 viruses isolated from some human H5N1 cases. Monitoring for antiviral resistance among avian influenza A viruses is very important and is ongoing.
Preventing Human Infection with Avian Influenza A Viruses
The best way to prevent infection with avian influenza A viruses is to avoid sources of exposure. However, people who work with poultry or respond to avian influenza outbreaks among poultry and are therefore potentially exposed to infected or potentially infected poultry are advised to follow recommended biosecurity and infection control practices; these include careful attention to hand hygiene and use of appropriate personal protective equipment. In addition, HPAI poultry outbreak responders should adhere to guidance from CDC and WHO and receive seasonal influenza vaccination annually and take prophylactic antiviral medication during an outbreak control response. Responders to LPAI outbreaks should consider this guidance as part of their response plan. Seasonal influenza vaccination will not prevent infection with avian influenza A viruses, but can reduce the risk of co-infection with human and avian influenza A viruses. Exposed persons should be carefully monitored for signs and symptoms that develop during and within 7 days after their last exposure to infected poultry or to environments potentially contaminated with avian influenza A virus-excretions/secretions.
Page last reviewed: November 25, 2011
Page last updated: November 25, 2011
Content source: Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD)
Since November 2003, nearly 600 sporadic cases of human infection with highly pathogenic avian influenza A (H5N1) virus (referred to as HPAI H5N1 or H5N1) have been reported by 15 countries in Asia, Africa, the Pacific, Europe and the Near East. HPAI H5N1 viruses have never been detected among wild birds, domestic poultry, or people in the United States. However, an outbreak caused by another subtype, highly pathogenic avian influenza A (H5N2), was reported in Texas in 2004. This was the first outbreak of highly pathogenic avian influenza among poultry in the United States in 20 years. The outbreak was reported in a flock of 7,000 chickens in south-central Texas. No transmission of highly pathogenic avian influenza A(H5N2) virus to humans was reported.
The World Health Organization (WHO) maintains situation updates and cumulative reports of human cases of avian influenza A (H5N1) [26 KB, 1 page]. Most human cases of H5N1 virus infection are thought to have occurred as a result of direct or close contact with sick or dead infected poultry.
Other subtypes of avian influenza A viruses also have infected humans, including low pathogenic avian influenza A (LPAI) viruses and highly pathogenic avian influenza A (HPAI) viruses. Public health authorities closely monitor cases of human illness associated with avian influenza A virus infections because of concerns about the potential for more widespread infections and transmission in humans. The spread of avian influenza A viruses from one ill person to another through prolonged, unprotected, close contact has been reported very rarely, and has been limited, inefficient and not sustained. However, because avian influenza A viruses have the potential to change and gain the ability to spread easily between people, monitoring for human infection and person-to-person transmission is extremely important for public health.
Top
Signs and Symptoms of Avian Influenza A Virus Infections in Humans
The reported signs and symptoms of avian influenza A virus infections in humans have ranged from eye infections (conjunctivitis) to influenza-like illness symptoms (e.g., fever, cough, sore throat, muscle aches) to severe respiratory illness (e.g. shortness of breath, difficulty breathing, pneumonia, acute respiratory distress, viral pneumonia) with multi-organ disease, sometimes accompanied by nausea, abdominal pain, diarrhea, vomiting and sometimes neurologic changes (altered mental status, seizures).
Detecting Avian Influenza A Virus Infection in Humans
Avian influenza A virus infection of humans cannot be diagnosed by clinical signs and symptoms alone, so laboratory testing is required. Avian influenza A virus infection is usually diagnosed by collecting a swab from the nose or throat during the first few days of illness. This specimen is sent to a laboratory, where they will either look for avian influenza A virus using a molecular test or they will try to grow the virus, or both. Growing avian influenza A viruses should only be done in laboratories with high levels of protection. If it is late in the illness, unless the person is critically ill, it may be difficult to find an avian influenza A virus directly using these methods. Sometimes it may still be possible to diagnose avian influenza A virus infection by looking for evidence of the body's response to the virus infection by detecting antibodies to the virus. This is not always an option because it requires two blood specimens (one taken during the first few days of illness and another taken some weeks later) and it can take several weeks to verify the results, and testing must be performed in a special laboratory, such as at CDC.
Top
Treating Avian Influenza A Virus Infections in Humans
CDC and WHO currently recommend oseltamivir, a prescription antiviral medication, for treatment and prevention of human infection with avian influenza A viruses. Analyses of available H5N1 viruses circulating worldwide suggest that most viruses are susceptible to oseltamivir. However, some evidence of resistance to oseltamivir has been reported in H5N1 viruses isolated from some human H5N1 cases. Monitoring for antiviral resistance among avian influenza A viruses is very important and is ongoing.
Preventing Human Infection with Avian Influenza A Viruses
The best way to prevent infection with avian influenza A viruses is to avoid sources of exposure. However, people who work with poultry or respond to avian influenza outbreaks among poultry and are therefore potentially exposed to infected or potentially infected poultry are advised to follow recommended biosecurity and infection control practices; these include careful attention to hand hygiene and use of appropriate personal protective equipment. In addition, HPAI poultry outbreak responders should adhere to guidance from CDC and WHO and receive seasonal influenza vaccination annually and take prophylactic antiviral medication during an outbreak control response. Responders to LPAI outbreaks should consider this guidance as part of their response plan. Seasonal influenza vaccination will not prevent infection with avian influenza A viruses, but can reduce the risk of co-infection with human and avian influenza A viruses. Exposed persons should be carefully monitored for signs and symptoms that develop during and within 7 days after their last exposure to infected poultry or to environments potentially contaminated with avian influenza A virus-excretions/secretions.
Page last reviewed: November 25, 2011
Page last updated: November 25, 2011
Content source: Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD)
