But the virus replicates over and over and over, so those add up with time. With a virus like HIV, it becomes very genetically diverse during infection of an individual, because HIV can replicate over and over again about once a day in an individual for years. So a lot of diversity is built up, which gives a virus a lot of flexibility. There are probably some mutations already present in the population in any infected, untreated individual that will make HIV resistant to specific drugs.
Can you explain the difference between a vaccine, which prevents infection, and an antiretroviral drug, which treats it? A vaccine is usually a component of the virus, or a form of the virus itself. In the case of rabies or some of the polio vaccines, it is attenuated—not causing disease, but still able to grow in the body. It induces a response from the body to make antibodies, so that anytime the antibodies see that virus again, they kill off the infection before it has a chance to cause disease.
An antiviral, on the other hand, is a small molecule, a fairly simple chemical—often, for example, a component of viral DNA or RNA that is slightly altered—that disrupts the process by which the virus replicates itself.
There are millions of viruses. Why do some cause illness in humans and other animals? There are almost as many different answers to that as there are viruses. But I can give you a general evolutionary explanation. Over long periods of evolution, you have a virus that comes into a host—a species—and spreads.
One of three things can then happen. One is that the virus can just die out for some reason—everybody can get immune, so the virus can no longer find a host, and it dies out. He and other scientists are starting to understand the ways we can better coexist with viruses.
So far, most of this research is in mice, but in one study Cadwell demonstrated that viruses can protect against intestinal damage caused by antibiotics. One day, this could lead to therapies or technology to help humans live in better harmony with viruses.
Whether or not the host gets sick is kind of more on us than them. Register or Log In. The Magazine Shop. Login Register Stay Curious Subscribe. SARS-CoV-2 virus particles, isolated from a patient and imaged using a transmission electron micrograph. Newsletter Sign up for our email newsletter for the latest science news. Sign Up. Already a subscriber? This enables us to visually investigate different stages of virus infection inside cells.
Electron microscopy can also be used to visualise whole virus particles, as shown in the image above. From these images, we can form 3D structures of whole virus particles by computationally assembling images of thousands of particles taken in different orientations, such as this example of a 3D EM rendering of SARS-CoV Such studies are really useful in working out how the virus gains access to our cells so we can work out how to use drugs to block it.
Evaluating the structure of the exterior of virus particles is also a great tool for identifying which antibodies can neutralise a virus , which can help produce more precise and effective vaccines. Crystallography allows us to view structures in even more detail, at the atomic level. To do this, you need a really pure sample of virus with no debris suspended in solution.
The liquid of the suspension is evaporated which causes crystallisation of the remaining solids including the virus. These align in a uniform manner to form crystals that can then be exposed to X-rays. The virus-first hypothesis suggests that viruses evolved from complex molecules of nucleic acid and proteins either before or at the same time as the first cells on Earth appeared, billions of years ago.
When a viral disease emerges, it is not always clear where it comes from. A virus exists only to reproduce. When it reproduces, particles spread to new cells and new hosts. The features of a virus affect its ability to spread. Some viruses can remain active on an object for some time. If a person with the virus on their hands touches an item, the next person can pick up that virus by touching the same object.
The object is known as a fomite. Viruses often change over time. Some of these changes are very small and do not cause concern, but others can be more significant. Significant changes could make a virus more transmissible, as has been the case with the B. They may also help the virus evade the immune system or existing treatments.
For example, doctors use several drugs in combination to treat HIV so that it is harder for the virus to develop resistance to treatment. Influenza viruses can also do so-called antigenic shift. This can happen if a host cell has become infected with two different types of influenza virus.
For instance, pigs can often serve as a mixing vessel for avian and human influenza viruses. Some viruses, such as HPV, can lead to cancer. The full impact of a virus can take time to appear, and sometimes there may be a secondary effect.
For example, the herpes zoster virus can cause chickenpox. The person recovers, but the virus may stay in the body. Years later, it may cause shingles in the same individual. Coronaviruses are a large family of viruses and include viruses that cause the common cold. However, it has changed many times since scientists first identified it in China. By September , scientists had logged over 12, mutations, and the development continues.
Some variants are more transmissible and more likely to cause severe illness than others. The main concern with new variants is the unpredictability of their impact. The main symptoms of COVID are dry cough , fatigue , and fever, but there are many possible symptoms.
Anyone who has symptoms should seek a test. It is also important to self-isolate until 10 days after symptoms appear and when no fever has been present for 24 hours.
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