Influenza (flu) |
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The 1977 Russian flu was an influenza pandemic that was first reported by the Soviet Union in 1977 and lasted until 1979. [1] [2] The outbreak in northern China started in May 1977, slightly earlier than that in the Soviet Union. [3] [4] The pandemic mostly affected a population younger than 25 or 26 years of age, [1] [5] [6] and was described as mild. [6] It was caused by an H1N1 flu strain which highly resembled a virus strain circulating worldwide from 1946 to 1957. [1] [2] [5] [6] Genetic analysis and several unusual characteristics of the 1977 Russian flu have prompted many researchers to say that the virus was released to the public through a laboratory accident, [4] [5] [7] [8] [9] [10] or resulted from a live-vaccine trial escape. [5] [11]
In May 1977, an outbreak of flu took place in northern China including Liaoning, Jilin and Tianjin. [3] [5] [12] [13] The strain was isolated and determined by Chinese researchers to be H1N1, which mostly affected students in middle and primary schools who lacked immunity to H1N1 virus. [3] Clinical symptoms were relatively mild. [3] Other areas in mainland China and British Hong Kong were also affected in the following months. [3] [8]
In the same year, the H1N1 strain was detected in Siberia shortly after the outbreak in China, and then spread rapidly across the Soviet Union, which was the first country to report the outbreak to the World Health Organization (the People's Republic of China was not a member of WHO until 1981 [14] ). [1] [4] [5] [6] Therefore, the pandemic was named "Russian flu". [15]
In 1977, Russian flu reached the United Kingdom. [16] The virus reached the United States in January 1978. [6] [12] The first outbreak in the U.S. was reported in a high school in Cheyenne, where the clinical attack rate was more than 70% but involved solely students. [2] [6] Even though infections were seen in schools and military bases throughout the U.S., there were few reports of infection in people older than 26, and the death rate in affected individuals was low. [2] [6]
Since late 1977, the H1N1 strain has begun to co-circulate with the H3N2 strain in humans, as seasonal flu. [1] [3] [15]
There have been various H1N1 strains. [5] The 1918 Spanish flu was caused by an H1N1 strain, and H1N1 strains afterwards became endemic and circulated around the world until 1957, when they all but vanished. (There were some isolated reports of other H1N1 strains such as the one in the early 1960s. [17] ) H1N1 reappeared in 1977 and the strain of the Russian flu was almost identical to one that had been isolated in 1950. [1] [2] [3] [4] [5] [6] [11] This feature of the 1977 strain has been interpreted as pointing towards an anthropogenic origin of the virus, and the pandemic is the only documented human epidemic believed to result from research activity. [5] [18] [19] [20]
The Russian flu was relatively benign. In 1977, Chinese researchers found uneven attack rates among different groups of students, as well as many mild and asymptomatic infections. [3] In the United States, some researchers estimate the influenza mortality rate (not the infection fatality rate or the case fatality rate) around 5 in every 100,000 population, less than that of the typical seasonal influenza (~6 in every 100,000 population). [5] [26] Most of the infected people were under the age of 26 or 25, [1] [5] [6] presumably because older people retained immunity from exposure to previous H1N1 strains. [11]
Contradicting these descriptions, one review article proposed that 700,000 people died due to the Russian flu pandemic worldwide and that the virus was "Identical with the "Spanish flu" virus". [27]
The 1918–1920 flu pandemic, also known as the Great Influenza epidemic or by the common misnomer Spanish flu, was an exceptionally deadly global influenza pandemic caused by the H1N1 subtype of the influenza A virus. The earliest documented case was March 1918 in the state of Kansas in the United States, with further cases recorded in France, Germany and the United Kingdom in April. Two years later, nearly a third of the global population, or an estimated 500 million people, had been infected in four successive waves. Estimates of deaths range from 17 million to 50 million, and possibly as high as 100 million, making it one of the deadliest pandemics in history.
Influenza A virus (IAV) is the only species of the genus Alphainfluenzavirus of the virus family Orthomyxoviridae. It is a pathogen with strains that infect birds and some mammals, as well as causing seasonal flu in humans. Mammals in which different strains of IAV circulate with sustained transmission are bats, pigs, horses and dogs; other mammals can occasionally become infected.
Avian influenza, also known as avian flu or bird flu, is a disease caused by the influenza A virus, which primarily affects birds but can sometimes affect mammals including humans. Wild aquatic birds are the primary host of the influenza A virus, which is enzootic in many bird populations.
Antigenic shift is the process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains. The term is often applied specifically to influenza, as that is the best-known example, but the process is also known to occur with other viruses, such as visna virus in sheep. Antigenic shift is a specific case of reassortment or viral shift that confers a phenotypic change.
Orthomyxoviridae is a family of negative-sense RNA viruses. It includes seven genera: Alphainfluenzavirus, Betainfluenzavirus, Gammainfluenzavirus, Deltainfluenzavirus, Isavirus, Thogotovirus, and Quaranjavirus. The first four genera contain viruses that cause influenza in birds and mammals, including humans. Isaviruses infect salmon; the thogotoviruses are arboviruses, infecting vertebrates and invertebrates. The Quaranjaviruses are also arboviruses, infecting vertebrates (birds) and invertebrates (arthropods).
Influenza vaccines, colloquially known as flu shots, are vaccines that protect against infection by influenza viruses. New versions of the vaccines are developed twice a year, as the influenza virus rapidly changes. While their effectiveness varies from year to year, most provide modest to high protection against influenza. Vaccination against influenza began in the 1930s, with large-scale availability in the United States beginning in 1945.
The Hong Kong flu, also known as the 1968 flu pandemic, was a flu pandemic that occurred in 1968 and 1969 and which killed between one and four million people globally. It is among the deadliest pandemics in history, and was caused by an H3N2 strain of the influenza A virus. The virus was descended from H2N2 through antigenic shift, a genetic process in which genes from multiple subtypes are reassorted to form a new virus.
Swine influenza is an infection caused by any of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) refers to any strain of the influenza family of viruses that is endemic in pigs. As of 2009, identified SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H2N1, H3N1, H3N2, and H2N3.
Flu season is an annually recurring time period characterized by the prevalence of an outbreak of influenza (flu). The season occurs during the cold half of the year in each hemisphere. It takes approximately two days to show symptoms. Influenza activity can sometimes be predicted and even tracked geographically. While the beginning of major flu activity in each season varies by location, in any specific location these minor epidemics usually take about three weeks to reach its pinnacle, and another three weeks to significantly diminish.
Influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus (IAV). Some human-adapted strains of H1N1 are endemic in humans and are one cause of seasonal influenza (flu). Other strains of H1N1 are endemic in pigs and in birds. Subtypes of IAV are defined by the combination of the antigenic H and N proteins in the viral envelope; for example, "H1N1" designates an IAV subtype that has a type-1 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein.
An influenza pandemic is an epidemic of an influenza virus that spreads across a large region and infects a large proportion of the population. There have been six major influenza epidemics in the last 140 years, with the 1918 flu pandemic being the most severe; this is estimated to have been responsible for the deaths of 50–100 million people. The 2009 swine flu pandemic resulted in under 300,000 deaths and is considered relatively mild. These pandemics occur irregularly.
Influenza A virus subtype H3N2 (A/H3N2) is a subtype of influenza A virus (IAV). Some human-adapted strains of A/H3N2 are endemic in humans and are one cause of seasonal influenza (flu). Other strains of H1N1 are endemic in pigs and in birds. Subtypes of IAV are defined by the combination of the antigenic H and N proteins in the viral envelope; for example, "H1N1" designates an IAV subtype that has a type-1 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein.
The genetic structure of H5N1, a highly pathogenic avian influenza virus, is characterized by a segmented RNA genome consisting of eight gene segments that encode for various viral proteins essential for replication, host adaptation, and immune evasion.
Pandemrix is an influenza vaccine for influenza pandemics, such as the 2009 flu pandemic. The vaccine was developed by GlaxoSmithKline (GSK) and patented in September 2006.
Influenza, commonly known as "the flu" or just "flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin one to four days after exposure to the virus and last for about two to eight days. Diarrhea and vomiting can occur, particularly in children. Influenza may progress to pneumonia from the virus or a subsequent bacterial infection. Other complications include acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing health problems such as asthma and cardiovascular disease.
The 2009 swine flu pandemic, caused by the H1N1/swine flu/influenza virus and declared by the World Health Organization (WHO) from June 2009 to August 2010, was the third recent flu pandemic involving the H1N1 virus. The first identified human case was in La Gloria, Mexico, a rural town in Veracruz. The virus appeared to be a new strain of H1N1 that resulted from a previous triple reassortment of bird, swine, and human flu viruses which further combined with a Eurasian pig flu virus, leading to the term "swine flu".
The 2009 flu pandemic in the United States was caused by a novel strain of the Influenza A/H1N1 virus, commonly referred to as "swine flu", that was first detected on 15 April 2009. While the 2009 H1N1 virus strain was commonly referred to as "swine flu", there is no evidence that it is endemic to pigs or of transmission from pigs to people; instead, the virus spreads from person to person. On April 25, the World Health Organization declared a public health emergency, followed concurringly by the Obama administration on April 26.
The pandemic H1N1/09 virus is a swine origin influenza A virus subtype H1N1 strain that was responsible for the 2009 swine flu pandemic. This strain is often called swine flu by the public media due to the prevailing belief that it originated in pigs. The virus is believed to have originated around September 2008 in central Mexico.
The 2009 swine flu pandemic vaccines were influenza vaccines developed to protect against the pandemic H1N1/09 virus. These vaccines either contained inactivated (killed) influenza virus, or weakened live virus that could not cause influenza. The killed virus was injected, while the live virus was given as a nasal spray. Both these types of vaccine were produced by growing the virus in chicken eggs. Around three billion doses were produced, with delivery in November 2009.
Influenza prevention involves taking steps that one can use to decrease their chances of contracting flu viruses, such as the Pandemic H1N1/09 virus, responsible for the 2009 flu pandemic.