Learning from the Past: Flu Pandemics in .NET framework

Generate QR Code 2d barcode in .NET framework Learning from the Past: Flu Pandemics

The term pandemic refers to an epidemic of an infectious disease that occurs over a large area, such as a continent or even the entire world The black plague that swept from Asia through Europe in the mid-1300s is a good example of a pandemic Flu pandemics can occur when a flu strain that appears in the human population is so different from the circulating strains that the worldwide population is completely susceptible As a result, this new flu is able to sweep rapidly through the entire world Often, influenza pandemics are given names related to the regions where the virus first appeared In an average year, the Centers for Disease Control and Prevention estimates that influenza kills more than 20,000 Americans The global total is harder to estimate accurately, but the World Health Organization places it at somewhere between 250,000 and 500,000 deaths per year Pandemic years see a much, much higher death rate sometimes into the millions

Scientists have information on flu pandemics dating from the pandemic of 1889 to the more recent 1977 pandemic By studying the genome sequences of the more recent strains and the antibodies of the victims in the more distant strains, researchers have been able to piece together the origin of these pandemic strains The following sections take you on a little stroll through the pandemic flus of the last hundred years

Because sequence information isn t available, scientists have to rely on seroarchaeology the search for antibodies in preserved tissue samples for these pandemics The antibodies in these tissue samples can t tell researchers about all the genes in the flu strains responsible for the pandemics, but they can identify the H and N proteins, because these proteins are the external parts of the flu virus that the body s immune system produces antibodies against So we know that the 1889 and 1900 pandemics were caused by an H2N2 and an H3N8 strain, respectively

The Spanish flu (1918)

This influenza pandemic strain is the first one for which researchers have complete sequence information Sequence analysis of the genes from this strain suggests that it was the result of an H1N1 avian influenza virus entering the human population This finding is important, particularly in light of recent concerns about the possibility that the rare but often fatal H5N1 avian flu will change to a form that can be easily spread between humans The Spanish flu is an example of a flu strain from one host (waterfowl) infecting a new host (us)

The Asian flu (1957)

The Asian flu strain (H2N2) contained 5 gene segments from the circulating 1918 strain and 3 new ones the different versions of the H and N genes, as well as a gene involved in RNA replication These changes were almost certainly the result of a reassortment event with an avian strain of influenza A, and the new strain replaced the H1N1 strain from which it was derived The Asian flu pandemic was the result of a reassortment event between the original H1N1 strain and an avian strain that contributed the 3 new genes These two strains ended up in the same host, the various segments got mixed up during the flu s replication, and out popped something new

The 1918 Spanish-flu pandemic killed more people than any other disease outbreak in human history It is estimated that between 20 million and 40 million people died of the flu during the 1918 1919 flu season Furthermore, although influenza is usually most fatal among the very young and the very old, the 1918 flu had very high mortality across all ages It was not until very recently that scientists learned the complete genome sequence of the 1918 flu No samples suitable for genome sequencing were known before that However, in 2005, viral nucleic acids were isolated from the bodies of victims who died in Alaska during the epidemic Their bodies had been buried in the Alaskan permafrost and had remained frozen until the present These frozen samples were sufficiently preserved that scientists could isolate the viral genetic material (RNA) from them Before the rediscovery of the 1918 flu, scientists thought that the 1918 pandemic originated in a fashion similar to the 1957 and 1968 pandemics that is, via the acquisition of several new genome segments from a reassortment event with an avian strain Scientists now know, however, that all eight segments of the 1918 strain are very similar to avian strains, and the current hypothesis is that the 1918 pandemic was the result of an avian strain entering the human population

The Hong Kong flu (1968)

When the Asian flu strain (H2N2; see the preceding section) went through a second reassortment with a different avian influenza strain, the H3N2 strain was born This strain had the same N gene but had acquired 2 new genes, including a new H gene This is another example of a reassortment event between a human strain and an avian flu strain This H3N2 strain replaced the H2N2 strain in the human population

The Russian flu (1977)

In 1977, the H1N1 flu last seen in humans in 1950 reappeared Because most people older than about 20 had been exposed to H1N1 flu, the resulting epidemic was not severe enough to be labeled a true pandemic, but it was certainly a significant event Scientists don t know exactly where this strain came from, but it has been suggested that it escaped from a laboratory somewhere Support for this hypothesis is not just the strain s sudden reappearance, surprising though that is More convincing is that the 1977 H1N1 was almost identical to the 1950 H1N1 in all those years, this strain hadn t been evolving