What is a virus?
A virus is a microorganism that is made up of protein and either DNA, RNA, or both. Viruses cannot reproduce on their own, and are dependent on host cells to do so. Viruses can cause infections and diseases in humans and animals.
What is influenza?
Influenza, or the "flu," as it is more commonly called, is a sickness caused by the influenza virus. Influenza can infect birds and humans, and usually causes headaches, muscle pain, chills, sore throat and coughing. Influenza is a seasonal virus and outbreaks usually occur during the cold half of the year.
How dangerous to humans is influenza?
Influenza usually only causes minor symptoms, but can be lethal for very young children, the elderly, and those with weak immune systems. Influenza usually kills 250,000 to 500,000 people in the world every year, and during "pandemic" years, or years when the virus spreads rapidly among large populations, it can kill millions of people.
What is RNA?
Ribonucleic Acid, or RNA, is a long chain of nucleotides found in all living things that contains genetic information. Viruses can have DNA, RNA, or both. Influenza is an RNA virus, meaning that it only has RNA to hold its genetic material.
Ribonucleic acid (RNA) is a molecule that has a single-stranded backbone made of alternating sugar (ribose) and phosphate groups. Attached to each sugar is one of four bases--adenine (A), uracil (U), cytosine (C), or guanine (G). essential biological molecule directing the coding, decoding, regulation and expression of genes.
What are surface proteins?
Cells are protected by a membrane that surrounds the cell, but this membrane also separates each cell from others. To allow the cells to interact, the cells have proteins that are on the outside of the membrane of the cell and interact with other cells. These proteins are called surface proteins.
What is antigenic shift?
Antigenic shift is a way in which two types of a virus can combine to form a new type. This most often happen with influenza, but can happen with a few other viruses too. Antigenic shift occurs when two different types of a virus infect the same cell. When each virus exposes its RNA to create new viruses, the new viruses that are created have a combination of RNA from both viruses.
Influenza viruses undergo antigenic shift, an abrupt, major change in the virus’s antigens that happens less frequently than antigenic drift. It occurs when two different, but related, influenza virus strains infect a host cell at the same time. Because influenza virus genomes are formed by 8 separate pieces of RNA (called “genome segments”), sometimes these viruses can “mate,” in a process called, “reassortment.” During reassortment, two influenza viruses’ genome segments can combine to make a new strain of influenza virus.
Reassortment results is a new subtype of virus, with antigens that are a mixture of the original strains. When a shift happens, most people have little or no immunity against the resulting new virus. Viruses emerging because of antigenic shift are the ones most likely to cause pandemics.
What is antigenic drift?
As a virus replicates, its genes undergo random “copying errors” (i.e. genetic mutations). Over time, these genetic copying errors can, among other changes to the virus, lead to alterations in the virus’ surface proteins or antigens. The human immune system uses these antigens to recognize and fight the virus.
In influenza viruses, genetic mutations accumulate and cause its antigens to “drift”— meaning the surface of the mutated virus looks different than the original virus. When influenza virus drifts enough, vaccines against old strains of the virus and immunity from previous influenza virus infections no longer work against the new, drifted strains. A person then becomes vulnerable to the newer, mutated flu viruses. Antigenic drift is one of the main reasons why the flu vaccine must be reviewed and updated each year, to keep up with the influenza virus as it changes.
What are the different types of RNA?
Different types of RNA exist in the cell: messenger RNA (mRNA), ribosomal RNA (rRNA), transfer RNA (tRNA) and transfer-messenger RNA (tmRNA). mRNA is the nucleic acid information molecule that transfers information from the genome into proteins by translation.
Another form of RNA is tRNA, or transfer RNA, and these are non-protein encoding RNA molecules that physically carry amino acids to the translation site that allows them to be assembled into chains of proteins in the process of translation.
Ribosomal RNA (rRNA) is the catalytic component of the ribosomes. The rRNA is the component of the ribosome that hosts translation. In the cytoplasm, ribosomal RNA and protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA and carries out protein synthesis. Several ribosomes may be attached to a single mRNA at any time.
Transfer-messenger RNA (tmRNA) is found in many bacteria and plastids. It tags proteins encoded by mRNAs that lack stop codons for degradation and prevents the ribosome from stalling.
How is RNA different from DNA?
RNA has a single strand of nucleotides while DNA has a double strand. RNA typically has a shorter chain of nucleotides than DNA. The sugar backbone of RNA has the sugar ribose instead of deoxyribose that’s in DNA. RNA has hydroxyl group making it more chemically labile than DNA and lowers activation energy of hydrolysis. DNA has complimentary base Adenine to Thymine, while RNA has Uracil s the complimentary base to Thymine.
How is the coronavirus changing?
From what has been observed thus far regarding the genetic evolution of SARS-CoV-2, it appears that the virus is mutating relatively slowly as compared to other RNA viruses. Studies to date estimate that the novel coronavirus mutates at a rate approximately four times slower than the influenza virus. Although SARS-CoV-2 is mutating, thus far, it does not seem to be drifting antigenically. It should be noted, however, that SARS-CoV-2 is a newly discovered virus infecting humans. There are still many unknowns, and our understanding of the SARS-CoV-2 virus continues to grow.
Coronaviruses do not have segmented genomes and cannot reassort. Instead, the coronavirus genome is made of a single, very long piece of RNA. However, when two coronaviruses infect the same cell, they can recombine, which is different than reassortment. In recombination, a new single RNA genome is stitched together from pieces of the two “parental” coronaviruses genomes. It’s not as efficient as reassortment, but scientists believe that coronaviruses have recombined in nature. When this happens, scientists identify the resulting virus as a “novel coronavirus.” The generation of a novel coronavirus, although occurring by a different mechanism than antigenic shift in influenza viruses, can have a similar consequence, with pandemic spread.
Alternatively, pandemic influenza viruses can sometimes arise, not by reassortment but by “zoonosis,” when an influenza virus that infects other animals, often birds or pigs, makes the leap into humans and starts to spread.
This happens with coronaviruses, too, with new human coronaviruses, or genes of new human coronaviruses, coming from ancestral coronavirus es that have infected other animals, such as bats, camels or pangolins.
To date, coronaviruses have acted like influenza viruses in generating outbreaks and now a pandemic from processes of recombination and zoonosis generating novel human coronaviruses (resembling the antigenic shift and zoonotic origin of new human influenza virus subtypes).
Human coronaviruses have mutated but have not undergone antigenic drift. This is good news for coronavirus vaccines. Nevertheless, given the similarities between the behavior of influenza viruses and coronaviruses, there is ample reason to remain vigilant for the possibility of future antigenic changes in SARS-CoV-2 and to be prepared to alter a potential COVID-19 vaccine, if necessary.
Influenza is caused by a host of various viruses. The job of disease control workers is to predict which of the flu viruses will most likely be present during the upcoming flu season. The workers then target the flu vaccine for those viruses that are expected in the greatest numbers and that are most virulent. Your challenge is to model the evolution of the influenza virus as it moves through a process that is called antigenic shift.
