On pages 118-120, Dr. Maolem describes how Paul Ewald, a leading evolutionary biologist specializing in infectious diseases, believes that the main factor of an infectious diseases virulence is the method the pathogen moves from host to host. One way microbes move from host to host is through close proximity allowing transmission through the air or close contact. Ewald describes how diseases using this particular mode of transportation are not particular virulent because it is a selective advantage leaving the host capable of moving and thus allowing them to move close to other potential hosts so the infectious agents can survive and reproduce. Another way microbes are transmitted is by using an intermediate organism to carry them to hosts, these organisms include mosquitoes, flies, fleas, and other similar organisms. Since these microbes don't need their actual host to spread, they are more virulent then the first type of disease. It is a selective advantage for diseases in this category to create as many infectious agents as possible as the more microbes there are in our blood, the higher the chance for an intermediate organism, like a mosquito, to pick up and further spread the disease, allowing it to survive and reproduce. The third type of transmission Ewald discusses is transmission through food or water. This case is exactly like the second type and differs only in the fact that the diseases of this category are spread through food and water rather than an intermediate organism. This relates to Big Idea 4: Biological systems interact, and these systems and their interactions possess complex properties.
Choose a different infectious disease to research and explain how it has evolved to produce symptoms that increase its ability to survive and reproduce. Be sure to include how your disease spreads in your response. Additionally, research what is currently being done to treat patients with your disease and describe how these treatments combat the disease and its spread. Finally, since the use of antibiotics can cause the disease to evolve to become resistant, discuss whether or not they should still be used, if not, provide and support an alternative solution.
Chris Yao chyao4@students.d125.org
Influenza A strains have an ability to undergo a process known as “reassortment” to create new, mutated strains of influenza. In order to understand the process of reassortment, we must first understand how an influenza virus infects a cell. Influenza is a particular virus whose genome is composed of 8 segments of RNA. The RNA segments of the influenza virus enter the cell and force the nucleus of the cell to copy the RNA of the virus. Then, the RNA segments are sent into the cytoplasm and incorporated into new virus particles. However, if a cell is infected with two distinct influenza viruses, the RNAs of both strains are copied in the infected cell’s nucleus and when new viruses are assembled at the plasma membrane, the new virus particles can inherit either all their RNA segments from one type of virus or inherit strains from each of the two viruses. The virus particles that inherit RNA segments from both viruses are viruses that have undergone reassortment. This particular process of reassortment is known as antigenic shift.
ReplyDeleteReassortment essentially creates a new type of virus that our immune system most likely has not encountered before. This makes the virus particularly dangerous and also raises the possibility of a pandemic in the human population. However, this antigenic shift serves as a selective advantage for Influenza A viruses that have undergone the process, since their phenotypic changes acquired after the reassortment process make them less likely to be destroyed by the human immune system. Like what we had learned in our immune system unit, the immune system recognizes viruses when antigens on the surface of the virus bind to immune receptors (antibodies) that are specific to these antigens. After battling this viral infection, the body produces more of these receptors to prevent re-infection by the same virus. However, if the virus has mutated to create a new, mutated version, the antibodies used to battle the previous viral infection are no longer effective. According to an article by Stanford University, Influenza A viruses have evolved mechanisms to jump species into fowl, farm animals, and humans, which means this antigenic shift also raises the mobility of viruses. For example, viruses that once only affected birds and pigs can jump from a bird to a pig. The pig could then acquire a viral strain that only affects pigs and humans. If reassortment occurs between these two viral strains, it could create a new species of virus that affects birds, pigs, and humans and can jump freely between all three species. This means that mutated influenza A viruses often “hitch a ride on an intermediate organism [....] these microbes rely on their hosts to carry them around and introduce them to new hosts” (Moalem 118-119). This serves as another selective advantage for viruses that can undergo reassortment, like Influenza A viruses. In fact, the H1N1 virus was the result of reassortment between avian, swine, and human flu strains.
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ReplyDelete(Part 2 of first response)
ReplyDeleteUnfortunately, according to MayoClinic, not much can be done for influenza A except for symptom relief, mostly using new antiviral drugs such as Tamiflu and Relenza. However, significant research is being conducted to isolate and sequence the genomes of Influenza A viruses. According to the New England Journal of Medicine, in the past several years, more than 46,000 RNA sequences of Influenza A have been deposited in the Influenza Virus Resource of the National Center for Biotechnology information. Their research has found that a total of 98% of all sequences of human Influenza A viruses deposited in the database have relatives with at least 99% nucleotide identity, proving that their is great similarity between influenza A viruses affecting humans. This gives us hope that the mutations to the virus are not drastic enough to completely compromise the human immune system.
However, according to Science Daily on March 25, 2013, scientists have designed a new vaccine against H5 Avian Influenza. Until recently, vaccines against H5N1 were relatively ineffective, but this new vaccine proved very effective when tested in mice and ferrets. What’s unique about this vaccine is that it uses attenuated viruses rather than “killed” viruses. Normally in vaccines, “killed viruses”, which are viruses broken up by chemicals or heat, are used due to the fact that they are much safer than attenuated viruses. Unlike more common vaccinations that are administered into the bloodstream, this vaccine is administered as a nasal spray, which actually mimics the natural infection process and, in turn, causes a stronger immune response. However, the reason why attenuated virus vaccines are so dangerous is because these viruses may exchange genetic material with other influenza viruses by reassortment. This may cause H5, a dangerous but hard to transmit virus, to transform into a virus that is dangerous and easy to transmit. Therefore, Daniel Perez of the University of Maryland led a team to design a safer version of this vaccine. He knew that influenza viruses carry their genetic material in eight segments, and during reassortment, viruses exchange these segments.
The scientists made the vaccine with an attenuated version of the H9 virus and added an H5 gene to one of the H9 virus segments in order to give resistance to the H5 virus. Then, segment 8 of this newly created virus, was split into two parts, NS1 and NS2. NS2 was moved into segment 2, which is adjacent to the polymerase gene, which is responsible for copying the virus’ genetic material during replication. By placing NS2 next to the polymerase gene, the polymerase gene was slower in its function, which interferes with the virus’ replication. Also, both NS1 and NS2 are needed for viral replication. Since these two genes are in different segments instead of in one segment, the probability that a reassorted virus will contain both these genes is much lower than if both these genes were in one segment. The research for this was also published in the Journal of Virology.
(Part 3)
ReplyDeleteWith regards to the issue on antibiotics, the fact that the use of them can cause certain bacteria to become resistant does pose a large threat. However, the resistance bacteria build to antibiotics can be slowed down if a person rarely uses antibiotics as a medical treatment. Also, if a certain bacteria does become resistant to a particular antibiotic, it can still be treated with a different antibiotic. That being said, antibiotics should still be able to be used to help cure bacterial infections, as long as they are not used too often.
Sources used: http://ih.stanford.edu/emerging%20diseases%20-%20nature.pdf
http://www.virology.ws/2009/06/29/reassortment-of-the-influenza-virus-genome/
http://www.mayoclinic.com/health/swine-flu/DS01144/DSECTION=treatments-and-drugs
http://familydoctor.org/familydoctor/en/drugs-procedures-devices/prescription-medicines/antibiotics-when-they-can-and-cant-help.html
http://www.sciencedaily.com/releases/2013/03/130325125649.htm
(Aaron Chai, achai4@students.d125.org)