Mutations can vary in severity from having zero consequence to majorly altering a protein and its function. Once a mutation occurs, if it changes the function of a resulting protein, a virus or organism is then changed. Because cells and viruses interact with the environment or surrounding cells, this change is either going to give the mutated cell or virus an advantage, allowing it to thrive more easily in its environment, or will make it disadvantaged, making it more difficult to survive.
This is a process called natural selection. If the mutation confers an advantage, the mutated sequence then spreads within a population and if the mutation confers a disadvantage, the mutated sequence dies out.
Consider the following scenarios actual or hypothetical and decide if the mutation in SARS-CoV-2 virus will be detected in an increasing portion of the population of viruses or will not be detected.
Explain your answer choice. Why, for that matter, did both these coronaviruses spill over into people at all, from their original bat hosts? As we face the current pandemic, it will be important to understand how SARS-CoV-2, the virus that causes Covid, is likely to evolve in the months and years ahead.
It might end up as just another cold virus, as may have happened to another coronavirus in the past. But it could also remain a serious threat or perhaps even evolve to become more lethal.
The outcome depends on the complex and sometimes subtle interplay of ecological and evolutionary forces that shape how viruses and their hosts respond to one another. Many of the scariest viruses that have caused past or current epidemics originated in other animals and then jumped to people : HIV from other primates, influenza from birds and pigs, and Ebola probably from bats.
So, too, for coronaviruses: The ones behind SARS severe acute respiratory syndrome , MERS Middle East respiratory syndrome and Covid all probably originated in bats and arrived in people via another, stepping-stone species, likely palm civets, camels and possibly pangolins, respectively.
Any or all of these factors are likely to differ from one host species to another, so viruses will need to change genetically — that is, evolve — in order to set up shop in a new animal. Host switching actually involves two steps, though these can overlap. But to become capable of causing epidemics, the virus also has to become infectious — that is, transmissible between individuals — in its new host. This suggests that the mutation first arose either in pangolins or an as yet unidentified species and happened to allow the virus to jump over to people, too.
One is in a region called the polybasic cleavage site , which is known to make other coronaviruses and flu viruses more infectious. Another appears to make the spike protein less fragile, and in lab experiments with cell cultures, it makes the virus more infectious. The mutation has become more common as the Covid pandemic goes on, which suggests — but does not prove — that it makes the virus more infectious in the real world, too. This evolutionary two-step — first spillover, then adaptation to the new host — is probably characteristic of most viruses as they shift hosts, says Daniel Streicker, a viral ecologist at the University of Glasgow.
Streicker sees this in studies of rabies in bats — which is a good model for studying the evolution of emerging viruses, he says, since the rabies virus has jumped between different bat species many times.
Since larger populations contain more genetic variants than smaller populations do, measuring genetic diversity in their samples enabled the scientists to estimate how widespread the virus was at any given time. The team found that almost none of the 13 viral strains they studied took off immediately after switching to a new bat species.
Instead, the viruses eked out a marginal existence for years to decades before they acquired the mutations — of as yet unknown function — that allowed them to burst out to epidemic levels. Not surprisingly, the viruses that emerged the fastest were those that needed the fewest genetic changes to blossom. SARS-CoV-2 probably passed through a similar tenuous phase before it acquired the key adaptations that allowed it to flourish, perhaps the mutation to the polybasic cleavage site, perhaps others not yet identified.
Many viruses that spill over to humans never do. About to viruses are known to infect people, but only about half are transmissible — many only weakly — from one person to another, says Jemma Geoghegan, an evolutionary virologist at the University of Otago, New Zealand. The rest are dead-end infections. Half is a generous estimate, she adds, since many other spillover events probably fizzle out before they can even be counted.
The big question now is: What happens next? Some predicted that the U. Health officials widely credited that vaccine with saving many lives. Which of the following is most likely to lead to a sudden, radical change in the influenza virus? True or false? The influenza vaccine always remains the same from year to year.
Article Menu [ ]. Vaccine Science [ ]. Biological Weapons, Bioterrorism, and Vaccines. Cancer Vaccines and Immunotherapy. Careers in Vaccine Research. Ebola Virus Disease and Ebola Vaccines.
Human Cell Strains in Vaccine Development. Identifying Pathogens and Transmission Vectors. Malaria and Malaria Vaccine Candidates. Passive Immunization. The Future of Immunization. Vaccines for Pandemic Threats. Viruses and Evolution. History and Society [ ]. Cultural Perspectives on Vaccination. Disease Eradication. Ethical Issues and Vaccines. History of Anti-vaccination Movements. Influenza Pandemics. The Development of the Immunization Schedule. The History of the Lyme Disease Vaccine.
The Scientific Method in Vaccine History. Military and Vaccine History. Vaccination Exemptions. Vaccine Injury Compensation Programs. Vaccine Testing and Vulnerable Human Subjects. Vaccine Information [ ]. Different Types of Vaccines. Government Regulation. Vaccine Development, Testing, and Regulation.
Vaccine Side Effects and Adverse Events. Vaccines for Adults. Vaccines for Teenagers. Vaccine-Preventable Diseases [ ]. Chickenpox Varicella. Haemophilus influenzae type b Hib. Hepatitis A and Hepatitis B. History of Polio Poliomyelitis. Human Papillomavirus Infection. Meningococcal Disease. Pertussis Whooping Cough.
0コメント