Where does the flu come from and why won't it go away?

By Tom McCutchan | Dec 15, 2011
Courtesy of: National Museum of Health and Medicine, Armed Forces Institute of Pathology, Washington, D.C. The Spanish Influenza. Emergency military hospital during influenza epidemic, Camp Funston, 1918 or 1919.

Over 60 percent of the infectious diseases that affect mankind were transmitted to humans from nonhumans. We constantly come into contact with animal viruses and bacteria in our daily lives. Most of the time they do not bother us at all, but occasionally they do. Animal “germs” become a real danger to humanity not so much when they pass from an animal to a human, but when they are able to take an additional step: To move from the infected human to another human.

The situation becomes even more dangerous when pathogens can live equally well in both human and nonhumans. Having an animal reservoir gives them a place to hide and survive even when people do find a drug or vaccine to protect themselves. The disease will still be out there, lurking among nonhumans and ready to attack us again once our defenses are down or once, through mutation and genetic reshuffling, it develops new offensive techniques.

Consider the different success rates of our vaccines for polio and yellow fever. There is no animal reservoir for polio and the disease all but vanished in regions where the vaccine became available. The virus had no where to go. The yellow fever virus, on the other hand, has a sanctuary in monkeys. The yellow fever vaccine is just as good as the polio shot, but since yellow fever has an alternate habitat in monkeys we will never be entirely rid of it, not as long as there are monkeys.

Influenza viruses are like the yellow fever virus but even more fortunate. Not only can some of the viruses pass from animal to human and then from human to human, they have more than one refuge available in the animal kingdom, most notably birds and pigs.

There are three basic categories of influenza virus that infect humans, and they are labeled types A, B, and C.

Type A, which has many subtypes, is the one that is most often associated with virulent infections in humans. Birds carry all known subtypes of Influenza A. Typically, wild birds do not become sick when they are infected with Influenza A viruses, and this makes them long-term, asymptomatic carriers (i.e., A Typhoid Mary with wings). Migratory birds rapidly disperse the flu virus along their seasonal paths.

Sometimes we wonder why we spend our tax dollars on projects like “A Two-Year Study of Ducks in Hong Kong” (1979). What that particular study established, however, was to have significant impact on world health. The authors of the study discovered that Influenza A viruses in ducks were up to something very peculiar, something that no one had seen before: They were exchanging genes among themselves to create new viruses. Looking further, scientists were even more astonished to find that Influenza A viruses that lived in birds were also capable swapping genetic information with flu viruses that normally infected other hosts, including pigs and humans.

Things came to a head when we discovered that the human viruses associated with the Asian flu pandemic of 1957 and the Hong Kong flu of 1968 contained genes from the flu viruses of birds and pigs. It now became clear that Influenza pandemics in human populations were associated with viral gene exchanges.

In 2005, a team of army scientists determined the structure of the virus that caused the most deadly of all influenza pandemics, the Spanish flu of 1918. They were given permission to take tissue samples from an Inuit woman who had died in 1918 and been buried in the permafrost.

The cold had preserved the infecting virus well enough that it could be analyzed and it appeared to be a bird flu virus. When samples of lung tissue from more victims of the 1918 flu were discovered in other places in the world, they, too, were analyzed and gave the same profile. Alone, these analyses were only circumstantial evidence. Scientists had to be able to synthesize the virus they had discovered and use it to cause the disease. The research team was able to do this and the mice they infected all developed flu-like symptoms and died. It was indeed a bird flu that had killed up to 8 percent of the world’s population.

Flu viruses are naturally created in endless varieties as a result of the accumulation of mutations and the exchange of genetic material. There seems to be little hope that we will ever develop a “universal” vaccine that will recognize and eliminate every type that poses a threat. Despite this, many excellent scientists are trying to do just that. Their challenge comes from the fact that the creation of new forms of the virus takes place in nature, outside of our realm. Our intellect is rarely a match for nature’s versatility. I suspect that when we have a vaccine that seems to work it will only be a short matter of time until a new virus arises that can evade it. I must admit, however, that I probably would have been against funding “ A Two Year Study of Ducks in Hong Kong.”

 

 

 

 

 

 

We gave Type A subviruses acronyms ( e.g., H1N1, H1N2 etc.) that related to the immunological response they elicited.

Are we better equipped to stop a pandemic than we were in 1918. If we depend solely upon stockpiling vaccines and drugs I would guess that we would not fair well despite our marvelous advances in biotechnology. It is very possible that the virus would not be of the H1N1 or H5N1 varieties that have received so much attention. Twitter might well spread the word faster than any means we had in 1918 but stimulating public awareness and public acceptance of steps that would need to be taken may in fact be more difficult.

 

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Are we facing a new flu pandemic? The Center for Disease Control (CDC) says that it is inevitable and probably with good reason. Unfortunately we now anticipate it somewhat like the expected earthquake on the San Andreas fault while ignoring the levees in New Orleans. Could something on the scale of the 1918 Spanish flu be on the way and catch us totally unprepared? Perhaps, but where should we direct our efforts.

 

Humans can be infected with influenza types A, B, and C viruses .Wild birds are the natural host for all known subtypes of influenza A viruses. Typically, wild birds do not become sick when they are infected with avian influenza A viruses. However, domestic poultry, such as turkeys and chickens, can become very sick and die from avian influenza, and some avian influenza A viruses also can cause serious disease and death in wild birds.

 

It apparently arose as a direct transfer of an avian virus to a human. If a cell is infected with two different influenza viruses, the RNAs of both viruses are copied in the nucleus. When new virus particles are assembled at the plasma membrane, each of the 8 RNA segments may originate from either infecting virus. The progeny that inherit RNAs from both parents are called reassortants. there appeared to be seven separate pieces of genetic information .central problem to slowing or eliminating the flu is that we aren’t the only ones that get it. have infected many different animals, including ducks, chickens, pigs, whales, horses, and seals. However, certain subtypes of influenza A virus are specific to certain species, except for birds, which are hosts to all known subtypes of influenza A. One important characteristic that helps to distinguish one flu virus from another flu virus.comes from determining which species it infects. There almost always variations on these themes. h The major exception is birds. Birds seem to host most flu viruses.

 

 

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