Swine flu and bird flu are both influenza viruses that can infect humans, but they are caused by different virus strains. While they share some similarities, there are important differences between swine flu (also known as H1N1 flu) and avian or bird flu viruses like H5N1 and H7N9.
What is swine flu?
Swine flu, or H1N1 flu, is a respiratory infection caused by an influenza A virus first identified in pigs. The H1N1 flu virus originated in pigs, but is now a human disease as well. There are three main types of influenza viruses that cause infection in pigs: H1N1, H1N2, and H3N2. The H1N1 swine flu virus can be spread from person to person through coughing, sneezing, or touching contaminated surfaces.
In 2009, a new strain of H1N1 swine flu emerged and caused a flu pandemic. This new “swine-origin” H1N1 virus contained a unique combination of influenza genes not previously identified in animals or people. The 2009 H1N1 pandemic virus is now a regular human flu virus known as “seasonal H1N1” that continues to circulate worldwide.
What is bird flu?
Bird flu, or avian influenza, refers to infection with avian (bird) influenza A viruses, such as H5N1, H7N9, and H9N2. These bird flu strains occur naturally in wild birds like waterfowl and shorebirds. They do not usually cause serious disease in bird populations, but can be highly infectious and fatal to domestic poultry.
Some subtypes of avian influenza A, such as H5N1 and H7N9, have caused outbreaks of varying severity in domestic poultry and wild birds in different countries around the world. On rare occasions, these viruses can also infect humans. This happens mainly through direct contact with infected birds.
H5N1 was the first avian flu virus known to occasionally infect humans, first identified in Hong Kong in 1997. Other bird flu strains like H7N9 and H9N2 have emerged more recently that can also cause human infections. However, sustained human-to-human transmission of these avian viruses has not occurred yet.
Similarities between swine flu and bird flu
Swine flu and bird flu do have some similarities since they are both influenza A viruses that can infect humans as well as animals:
- They have a similar viral structure – Influenza A viruses contain RNA as their genetic material and are enveloped viruses with a helical nucleocapsid.
- Their surface proteins hemagglutinin (HA) and neuraminidase (NA) allow them to enter and exit host cells during infection.
- Both can cause respiratory illness in humans, with symptoms like fever, cough, sore throat, runny nose, muscle aches, headaches, and fatigue.
- Rarely, they may also cause severe complications like pneumonia, respiratory failure, and even death.
- They have the potential to cause pandemics if a strain emerges that can spread easily between people.
- Control measures are similar – vaccination, antiviral drugs, hygiene, and social distancing.
Key differences between swine flu and bird flu
However, there are some important differences between swine flu and avian influenza viruses:
Swine Flu | Bird Flu | |
---|---|---|
Virus type | Influenza A virus subtype H1N1 | Influenza A virus subtypes like H5N1, H7N9, H9N2 |
Main natural hosts | Pigs | Wild aquatic birds like ducks and geese |
Infectivity in humans | Easily spreads between humans via droplets and aerosols | Harder to transmit between humans, but some strains have infected people through close contact with birds |
Human fatality rate | Less than 0.1% | Around 60% for H5N1, 30% for H7N9 (but likely an overestimate due to mild cases being missed) |
Ongoing circulation in humans | H1N1 is a seasonal flu virus that circulates year-round | Only occurs sporadically when transmitted from birds to humans |
Pandemic potential | Caused the 2009 H1N1 flu pandemic | Concerning, but no sustained human-to-human transmission yet |
Geographic distribution | Present worldwide | Mainly in Asia and Egypt |
Transmission differences
One major difference between swine flu and bird flu is their transmissibility among humans. The H1N1 swine flu virus spreads easily from person-to-person through respiratory droplets and contact, similar to seasonal flu viruses. Bird flu viruses do not yet transmit easily between people.
However, some avian influenza strains like H5N1and H7N9 have displayed limited ability to spread between close contacts, particularly those caring for infected patients. But ongoing human-to-human transmission has not occurred yet beyond small clusters of infections.
Severity and fatality rates
Swine flu generally causes a mild, self-limiting illness in most people infected, with a fatality rate estimated at less than 0.1%. By contrast, some strains of avian influenza like H5N1 and H7N9 can be far more severe in humans.
About 60% of reported H5N1 cases and 30% of H7N9 cases have resulted in death. However, this high fatality rate is likely an overestimate because milder infections are less likely to be tested and confirmed. The true fatality rate for bird flu is difficult to determine precisely but is still thought to be much higher than that of seasonal flu viruses.
Geographic spread
The H1N1 swine flu virus spread globally and is now a regular seasonal flu virus found worldwide. In contrast, strains of avian flu like H5N1and H7N9 have not yet shown sustained ability for human transmission and remain restricted to certain affected regions.
H5N1 is largely limited to certain Asian and African countries. H7N9 has caused most human cases in China. Other bird flu virus strains cause mainly sporadic infections linked to contact with infected poultry and have not acquired the ability for ongoing transmission between humans.
Conclusion
In summary, swine flu and bird flu are both influenza A viruses that can on rare occasions infect humans. However, important differences exist between them with regards to their viral subtypes, natural hosts, severity, ongoing transmission, and geographic distribution.
The H1N1 swine flu virus spreads readily from person-to-person like seasonal flu, whereas avian influenza virus transmission is mostly limited to birds with only sporadic human cases acquired through direct contact with infected poultry. influenza Viruses like H5N1 and H7N9 can cause more severe disease but currently pose a limited pandemic risk due to lack of sustained human transmission.
Ongoing surveillance is important to monitor these viruses for any evolution that enables more efficient human-to-human spread. Vaccination and influenza pandemic preparedness plans remain vital to reduce the threat posed by both swine and bird flu viruses to human health.