Tuesday, March 9, 2010
Battle Against Viruses
On pages 130-132, Coyne discusses how the the quick evolution of viruses has changed the options humans have to battle deadly diseases. How do these viruses evolve so quickly? What process do viruses show at work? What potential effect could this have on society and how we treat viruses in the future?
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Bacteria has the ability to reproduce both asexually and sexually. "Some bacteria can reproduce as often as once every 20 minutes! However, bacteria have to have certain conditions in which to reproduce. These conditions are not often met, and that is one thing that keeps bacteria from growing out of control." (http://www.lanesville.k12.in.us/lcsyellowpages/Tickit/Carl/bacteria.html) For this reason, bacteria is able to evolve faster because evolution occurs after thousands and thousands of generations. If some bacteria can reproduce every two minutes, and it is in the right conditions, then it can produce thousands and thousands of generations in less than a year. This increases the chances bacteria have of evolving because they reproduce so quickly. A virus reproduces by "implanting its genetic makeup into the hosts cell. As the host cell reproduces, its replicates have the genetic makeup of the virus instead of the original cell. The virus continues like this until stopped by the host's immune system or until the host dies." (http://www.ehow.com/how-does_4567511_viruses-reproduce.html) Viruses can reproduce much quicker than larger species such as humans or other animals, because they only need a host cell in order to pass on their genetic makeup. Cells divide more often and quicker than many other animals reproduce, so viruses have more generations of their genes in a shorter amount of time just like bacteria. For these reasons, viruses and bacteria can evolve quicker because they have more generations in a significantly shorter amount of time than do many other species. This increases their chances of evolving. This causes a huge threat to humans because it is harder for us to fight off infectious disease and find drugs that are still able to kill bacteria or viruses. In order to prevent this mutation and evolution from occuring, we must take caution when we dispose of viral and bacterial resistant drugs. This way we can prevent bacteria and viruses from being exposed to these drugs and stop them from mutating and gaining resistance to our drugs. People must also stop the abuse of antibiotics so that they are only used when necessary. This will limit the amount of bacteria and viruses exposed to the drugs, and it will limit the amount of antibiotics exposed to the environment. According to, http://www.who.int/drugresistance/en/ , "two factors drive the rise and spread of resistant microbes: 1. Overuse and misuse of antimicrobials and 2. the spread of resistant organisms between individuals, communities, and countries." If people are informed of this and take caution, then we can slow down the mutation and evolution of many bacteria and virus species.
ReplyDelete(Part 1 of 2)
ReplyDeleteLexi did a nice job of describing how bacteria and viruses are able to evolve so quickly and how this process illustrates natural selection at work. However, she didn’t talk too much about how viruses affect humans, how humans treat them, and how these treatments affect the evolution of viruses. Viruses can enter the body cells because they are coated with a glycoprotein envelope, which can bind to the plasma membrane and facilitate the virus’ entry into the cell. Once inside, the viral capsid is digested, and the viral genetic material is released into the cell, which copies the RNA or DNA. Sometimes, the virus is a retrovirus that utilizes reverse transcription, a process in which the virus use reverse transcriptase to convert its RNA into DNA, which is then inserted into the cell’s DNA. Once the virus’ genetic material is copied, the cell begins to produce more of the viral proteins, which are assembled around the copied viral RNA or DNA. Finally, the virus copies exit the cell and infect other cells (Campbell 388).
Naturally, the production of viruses impairs the normal function of body cells, but luckily we have drugs to combat the viruses. Vaccines are the main method of preventing viruses from infecting a host; they are essentially specimens of the virus that have been killed and then introduced into a person’s body so that the immune system learns to recognize the viral proteins and builds up a defense against them (Wikipedia). Then, when an active version of the virus enters the body, the immune system recognizes it and deactivates it.
(Part 2 of 2)
ReplyDeleteUnfortunately, viruses can reproduce quickly, and their genetic material has a high propensity for mutations since errors in transcription of their RNA or DNA are not corrected by proofreading (Campbell 391). These two factors result in different strains of a virus being created, and a vaccine is only effective against the original strain. An example of strains of a virus can be seen in influenza, which is notorious for its different strains and the hit-and-miss reliability of vaccines against it. There are ten different serotypes (ten different strains) of influenza A, the influenza that has the greatest effect on humans, and each year a vaccine can only be developed to protect against a few of these strains (Wikipedia). For example, this past winter, the flu vaccine developed by the government protected against the H1N1 and H3N2 versions of influenza (http://www.cdc.gov/flu/flu_vaccine_updates.htm). This protected Americans fairly well against those strains of the flu, but offered no protection against other strains, such as H5N1. H5N1 is considered a threat for pandemic because no vaccine against it has been developed and it produces a very high mortality rate among the humans it infects. The bottom line is that viruses such as influenza can have many varieties, develop these varieties quickly, and thus evade the vaccines we have developed to combat them.
Another development may help, though: antiviral drugs. These medicines aim to disrupt a part of the viral life cycle, such as entry into a cell or transcription of genetic material, rather than training the body’s antibodies to recognize a viral protein (Wikipedia). One example of an antiviral drug is AZT, which Coyne says is designed to “prevent the HIV virus from replicating in an infected body” (131). It does this by interfering with the virus’ reverse transcriptase. However, recent studies show that the HIV virus has begun to acquire resistance to AZT by developing mutations in its reverse transcriptase. This is natural selection at work, because viruses with mutant reverse transcriptase enzymes can produce more of themselves, while those that can be stopped by AZT do not reproduce. One way society has resolved to deal with this problem is by adding more drugs to AZT, creating a “cocktail” (133) that HIV patients must take in specific doses at specific times of the day (Wikipedia). The additional drugs affect different parts of the viral cycle, creating a system of checks to ensure that the virus will be stopped somewhere within its cycle. However, eventually the HIV virus will mutate to such a degree that none of the steps in its cycle are stoppable by current drugs. The only answer for society is to look for a way to stay one step ahead of the virus, perhaps by finding a way to disable mutations.