![]() ![]() This is why since the turn of the 20th Century, pandemics have only occurred in 1918, 1957, 1968 and most recently, in 2009. The good news is that these requirements are met in nature quite infrequently. If the new influenza virus can only replicate in the lungs, it is not as likely to spread. This makes it easier to spread from person to person. Lastly, the new virus must be introduced into people and be able to replicate in the nose and throat. Additionally, the bird and human influenza viruses must contain a gene or genes for hemagglutinin or neuraminidase surface proteins to which virtually no one is immune. This typically only happens on small farms where pigs, birds and people are in close contact, such as in Asia where crowded conditions are more likely. First, influenza viruses from both birds and people must co-infect a pig. Luckily for humans, this does not happen very often. In order for a new influenza virus to cause a pandemic, a lot of things must fall into place. Fortunately, most of the novel viruses that are produced during this process do not lead to pandemics. Virtually everyone in the world is susceptible to the new virus. This is when an influenza pandemic can occur. Antigenic shift can produce a version of influenza virus that no person’s immune system has antibodies to protect against. Because the genes in the resulting virus are dramatically different, this is called antigenic shift.Īntigenic shift is more concerning than antigenic drift. During replication, both versions of influenza virus release their genetic material into the pig cell. Then, the genes from the different viruses can “mix” creating new versions of influenza virus. Both human and bird influenza viruses can attach to and enter the lung cells of a pig. As shown in the animation, pigs are a great vessel for enabling this. This happens when two kinds of influenza virus infect the same cell and share their genes to make a new version of influenza. Influenza viruses can undergo a more dramatic, and sometimes more deadly, change. This happens so often that we typically need new versions of the influenza vaccine each year. Antibodies now have trouble recognizing the changed virus. Over time, these small changes accumulate, so that your immune system becomes less effective at protecting you from the virus. As it reproduces, its genes change slightly. View the animation Antigenic Drift: How the Influenza Virus Adapts Today, scientists study changes to genes to learn more about many different viruses, bacteria and genetic-based diseases. Maurice Hilleman cleverly used this idea to discover how influenza virus changes over time so it can continue to infect people and animals. When the photos are put together, they form a movie that compresses hours or days into a matter of seconds. A camera is set up to take a series of photos over time. ![]() We can do something like this with time-lapse photography. Imagine what you’d see if you could speed up time.
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