History of the Flu and Pandemics

What strains were responsible for major pandemics of the 20th century?

Hoda Hai writes: The strains responsible for the pandemics of the 20th century were as follows: in 1918, the influenza A virus strain of H1N1 originating in Spain, in 1957 the H2N2 strain originating in Asia and in 1968 the H3N2 strain originating in Hong Kong.

Lyndsay Berman writes: Three influenza pandemics in the 20th century, each following a major genetic change in the virus, killed millions of people all over the world. They occurred in 1918, 1957, and 1968. All 3 have been informally identified by their presumed sites of origin as Spanish, Asian, and Hong Kong influenza, respectively. They are now known to represent 3 different antigenic subtypes of influenza A virus: H1N1, H2N2, and H3N2, respectively.

Dan Szyprowski writes: In 1918 the pandemic that occurred was an outbreak of the Spanish flu of the H1N1 strain. The origin of this pandemic was never truly discovered.

Why did they die back?

Hoda Hai writes: These pandemics finally died back was partly because of natural immunity due to the fact that there was no known cure. Eventually, the only people left would be the ones who are naturally immune to the disease. If there is a cure and the public responds fast enough, medications and vaccines can be administered to the general public. Lastly, the morphing of a virus can sometimes be helpful by making the virus less deadly due to some changed characteristics.

Lindsay Berman writes: Pandemics “end” for a variety of reasons. In major, uncontained pandemics with no known cure, only those who have a natural immunity, or those who will never be exposed, will survive. Eventually, these are the only people left. Or, if public response is fast enough, medications and vaccines can be distributed to the general public, slowing the spread. Also, the virus may morph and change its characteristics, such as becoming less severe.

Dan Szyprowski writes: The strain never truly died off but simply mutated into new strains of virus. Also some viruses of the H1N1 strain were discovered in frozen corpses in a remote Alaskan village. Extracting the virus will provide more information on the origins of the 1918 strain. In 1957 another major pandemic occurred which was caused by the H2N2.

How did they figure them out?

Hoda Hai writes: Scientists found out about the genetic variations in the viruses through simply isolating patients who had the illness already. Once this was done, they used detection and used sequence-based typing of human influenza virus strains to narrow down the strains. Electrophoresis-based sequencing technology has been used as the standard for most sequencing of the DNA genomes.

Lindsay Berman writes: Identification of genetic variations of influenza viruses is essential for epidemic and pandemic outbreak surveillance and determination of vaccine strain selection. The virus can be isolated from patients afflicted with the illness. Once the virus is isolated, modern technology can be used to demonstrate simultaneous detection and sequence-based typing of human influenza virus strains. Electrophoresis-based sequencing technology has been used as the standard platform for DNA and genome sequencing.

Dan Szyprowski writes: The epidemic was quickly recognized and a virus was recovered from the outbreak and sent to Washington DC for study. The virus was quickly recognized as an influenza type A virus by complement fixation tests. 11 years after the 1957 outbreak of the virus the H2N2 disappeared and
was replaced by the H3N2. In 1968 a new epidemic occurred in mainland China caused by the H3N2 strain. It was first detected in Hong Kong and September and the first signs of the disease in the USA appeared in December. Approximately 33 000 people died
making it the most mild pandemic of the century. Thanks to mass vaccinations in the
USA and better antibiotic technology, this virus was never too widespread.

Where are they now?

Hoda Hai writes: As to the question of where the viruses are now, many have either died out completely or the virus is in such a state that it cannot affect humans any more. Also, if it is left, it may only be contained in small, isolated areas.

Lindsay Berman writes: They are in very small numbers in isolated areas. The viruses also may have either died out completely, or the virus is in such a state that it cannot cross the human species barrier.

What was the key to the deadliness of the strain of 1918?

Hoda Hai writes: The 1918Spanish Flu pandemic was particularly deadly for several reasons. First, it was thought to have originated in China in a rare genetic shift with a recomibation of its surface protiens. This made it very different from the strains people were used to and made it able for humans to lose most of their natural immunity to it. Also, travel time that was very rapid led to its spread around the world in a short amount of time.

Ashley Guiliani, Sean, Joe, Marty, and Josh write: The key to the 1918 strain’s deadliness seems to be the effect of its H protein on molecules that are part of the host’s immune response, called pro-inflammatory cytokines. The severity of many viral diseases results from over-induction of this immune response.

Scientists found that hybrid viruses carrying the 1918 H induced cytokines that activated a class of white blood cells called macrophages. It also attracted white blood cells called neutrophils into the alveoli, or air sacs, of the lungs. There, instead of just fighting infected cells, they caused runaway damage to lung tissue.

Experiments elsewhere found that equipping viruses that already caused flu symptoms in mice with the 1918 H resulted in a flu hybrid which made mice sick, even though the H from a human virus should not have been able to do this.

Kawaoka’s team went one step further by putting the 1918 H into human flu viruses that do not normally affect mice. This turned the viruses into mouse-killers.

The 1918 H even made a virus that normally kills mice even more lethal. In every case, the 1918 hybrid replicated more, invaded the deeper tissues of the mouse lungs, and caused nastier lesions. Similar experiments with the N protein from the 1918 flu human strain showed no such effect.

Lindsay Berman writes: It is thought to have originated in China in a rare genetic shift of the influenza virus. The recombination of its surface proteins created a virus novel to almost everyone and a loss of herd immunity. Travel in this time also led to the worldwide spread of the virus.

Dan Szyprowski writes: The key to the deadliness of the 1918 Spanish Flu was a rare genetic shift in the influenza virus that has been said to originate in China. This like the current bird flu was thought to originate from birds. Though, bird viruses usually don't infect humans because human and bird virus hemagglutinins interact with different cell receptors. Though for bird viruses to infect people, their hemagglutinins must change so that they can attach to the human receptors in the cell. The structure of the 1918 HA had changed making it capable of attaching to human cells, thus allowing human-to-human transmission. This was done through the recombination of the surface proteins in the virus, which created a new super virus that most people did not have immunity to. Also, since World War I was raging the shipment of troops and supplies around the globe quickly spread the virus to all countries around the globe.

http://virus.stanford.edu/uda/
http://news.nationalgeographic.com/news/2004/02/0205_040205_spanishflu.html

What has been performed in order to study viruses from pandemics of the past?

Hoda Hai writes: In order for us to study pandemics of the past, we use samples of isolated viruses that have been reconstructed and we study them. Tissue samples have been taken from victims of the flu pandemics as well as blood from those who survived to test for antibodies. It is crucial for the scientific community of the world to study these past pandemics in order to prevent some in the future.

Lindsay Berman writes: Using samples from the past, along with modern technology, viruses have been isolated, reconstructed, and studied. Tissue samples have been taken from past victims, and people who survived the pandemics have had blood drawn to test for antibodies. The goal has been to find the causes of past pandemics in order to prevent them in the future.

Dan Szyprowski writes: Currently there is a lot of research and studying going on about the major pandemics of the past, because currently we are in loom of another one. One of these extinct viruses from the past is smallpox. The last known case of smallpox was in the late 1970's and during that period scientists and researchers fought to eradicate this horrible virus. They did this over ten years through a strategy of massive ring vaccinations over the entire world. Currently smallpox and other viruses that have caused pandemics are being studied in highly protected laboratories. An example of such study is through “blood samples provided by those infected with a recent outbreak of monkey pox and those who were exposed but remained illness-free can give us insight into how the human body fights off poxviruses, including the number one killer -- smallpox. Tracking immune responses as they occur is tremendously helpful not only in learning how to develop better vaccines, but in providing us an opportunity to observe firsthand how the immune system attacks and destroys an invading pathogen. Watching how these interactions unfold over time helps us to expand our basic understanding of this complex disease."

Though here at these laboratories there is high amount of security to prevent the outbreak of one of these deadly viruses into the normal population. At these secret laboratories scientists test and look at these viruses searching on how they work and ways to stop them in case there ever is another outbreak. This research is very important and necessary because it can help prevent and stop terrorist attacks using biological weapons.

http://www.medicalnewstoday.com/medicalnews.php?newsid=28811

Back