Types of flu
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Types of Influenza: An Overview
Introduction to Influenza Viruses
Influenza, commonly known as the flu, is an infectious respiratory disease caused by influenza viruses. These viruses belong to the orthomyxovirus family and are categorized into four main types: A, B, C, and D. Each type has distinct characteristics and impacts on human health1 2 4.
Influenza Type A
Characteristics and Subtypes
Influenza A viruses are known for their ability to cause both seasonal epidemics and pandemics. They are highly variable and can infect a wide range of hosts, including humans, birds, and other animals. Influenza A viruses are further classified into subtypes based on two surface proteins: hemagglutinin (HA) and neuraminidase (NA). There are 18 known HA subtypes (H1 to H18) and 11 NA subtypes (N1 to N11)2 5 7.
Historical Pandemics
Influenza A has been responsible for several major pandemics, including the Spanish flu in 1918, which caused approximately 50 million deaths, the Asian flu in 1957, and the Hong Kong flu in 19681 5. The H1N1 pandemic in 2009, also known as swine flu, was another significant outbreak caused by a novel strain of the H1N1 virus1 10.
Influenza Type B
Seasonal Epidemics
Influenza B viruses primarily infect humans and are a common cause of seasonal flu epidemics. Unlike type A, influenza B viruses do not have subtypes but are divided into two main lineages: B/Yamagata and B/Victoria4 5. These viruses contribute significantly to the annual flu burden, especially in children and the elderly1 4.
Recent Trends
During the 2019-2020 flu season, influenza B cases were notably higher than influenza A cases, a trend that was unusual compared to previous years. This shift was observed during the COVID-19 pandemic, indicating potential interactions between the two viruses4.
Influenza Type C
Mild Infections
Influenza C viruses cause mild respiratory illnesses and are less common compared to types A and B. They primarily infect humans and are not known to cause significant epidemics or pandemics1 2 7.
Influenza Type D
Potential Threat
Influenza D viruses primarily infect cattle and are not known to infect humans. However, there is a potential for these viruses to cross the species barrier and cause infections in humans, which warrants ongoing surveillance1 7.
Conclusion
Understanding the different types of influenza viruses is crucial for developing effective prevention and treatment strategies. While types A and B are the primary culprits behind seasonal flu epidemics and pandemics, types C and D also pose potential risks. Continuous monitoring and research are essential to mitigate the impact of these viruses on public health.
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Most relevant research papers on this topic
Influenza: A Unique Disease
Influenza is a highly contagious viral disease caused by four types of viruses, with yearly outbreaks causing millions of cases and 250,000 to 500,000 deaths worldwide.
Very Rigorous JournalInfluenza Virus Infections
Influenza viruses are highly contagious and can cause severe symptoms, with annual vaccination being the best preventative measure against the virus.
Clinical characteristics and severity of influenza infections by virus type, subtype, and lineage: A systematic literature review
Influenza clinical presentation and severity differ across virus types, subtypes, and lineages, with higher hospitalization and death rates in seasons dominated by A(H3N2) viruses.
Systematic Review
Highly CitedInterplay of Influenza A/B Subtypes and COVID-19
During the COVID-19 pandemic, influenza B cases were higher than influenza A cases, with flu B peaking at the same time or earlier than flu A, a deviation from previous flu trends.
Influenza
Seasonal influenza infection presents clinically from asymptomatic to fulminant, with potential pandemic threats, and new approaches are needed for prevention and treatment management.
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Influenza is an infectious respiratory disease caused by influenza A and B viruses, causing significant human and animal health impacts.
Highly CitedUnderstanding the symptoms of the common cold and influenza
New knowledge of cytokines helps explain some previously folkloric symptoms of colds and flu, improving our understanding of their mechanisms.
Highly CitedA/H1N1 Influenza
A/H1N1 influenza is a respiratory disease caused by a type of influenza virus.
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