Why viruses cause disease

Being virulent was not the primary goal. This explanation for bacterial virulence is straightforward and compelling: virulence is not directly selected for during evolution but comes along for the ride.

Can it be applied to viruses? All eukaryotic viruses must encode at least one protein that antagonizes host immune responses, otherwise they would be eliminated. These immune evasion proteins are certainly virulence factors: in general, when they are deleted or altered, the capacity of the virus to cause disease in a host is reduced. Like bacterial virulence, viral virulence might be collateral damage incurred by having to evade immune responses.

This hypothesis is attractive but seems overly simplistic. If the ubiquitous and benign circoviruses did not evade host responses, then they would be eliminated from the human population. The reasons why some viruses are virulent and others are not remain elusive. It is possible to reduce viral virulence by mutation, but this type of experiment does not reveal why viruses cause disease. The inverse experiment would be more informative: to select from a population of avirulent virus those that can cause disease.

The results of such an experiment would help to identify the selection pressures that allow viruses to evolve to virulence. 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. If a person has difficulty breathing , they should seek emergency medical attention. However, special T cells, known as cytotoxic T cells, can recognize cells that contain viruses, and release substances that kill those cells. Some viruses can escape detection by cytotoxic T cells, but other immune cells — natural killer cells — can cause the cell containing the virus to die.

In addition, body cells that contain a virus emit proteins called interferons, which warn other cells that a virus is present. This gives healthy cells a chance to defend themselves by changing the molecular makeup of their surface. Antibodies can also help fight a virus before it enters a cell.

They do this by neutralizing or damaging the virus or by changing its features so that it can no longer enter healthy cells. Antibiotics treat bacterial infections , but they cannot treat a viral infection. People will need either a vaccination to prevent infection, or antiviral drugs to treat any symptoms. Sometimes, the only option is symptom relief. In recent decades, scientists have developed antiviral drugs, largely in response to the AIDS pandemic.

These drugs do not destroy the virus, but they slow or prevent its development. With antiviral treatment for HIV, for example, the level of virus in the body can become so low that tests cannot detect it. At this point, it becomes untransmittable, which means that a person cannot pass the virus on to another person. Antivirals are also available to treat infection with HSV, hepatitis B , hepatitis C , influenza, shingles, and chickenpox.

Tamiflu is an example of an antiviral drug. People can use it to manage influenza. Some vaccines have succeeded in eliminating diseases such as smallpox, which experts believe has been around for at least 3, years. Here are some ways a virus vaccination may work:. Currently, vaccinations exist for polio, measles, mumps, rubella, COVID, and various forms of the flu, among other conditions.

Vaccination can dramatically reduce the likelihood of becoming seriously ill due to a virus, as well as the risk of passing a virus on to others.

If there is an outbreak, it usually affects people who have not had the vaccine. As a result, the risk of disease increases dramatically, and an outbreak can occur. Health experts encourage people to have this vaccine to protect themselves and others. Viruses are biological entities that are present in all living beings.

This may be the case with the virus causing CoVID, so stopping it may take more time. Antiviral drugs can work with some viruses, but the mutation rate of most viruses means that they become resistant to antivirals very quickly. The best treatment is to give the patient the best tools to allow their own body to fight off the infection.

This usually means rest and keeping hydrated. Virus infection can suppress the immune system, so patients should be monitored for secondary infections that might require other treatments. Prevention is important. Sick people need to be isolated, and healthy people need to take precautions. Most respiratory viruses are not transmitted just by breathing them in from sick people, but by getting them on your hands from tiny droplets that sick people distribute by coughing or sneezing, and then touching your face.

Good hand-washing is important! Sign up for our weekly newsletter. Portsmouth Climate Festival — Portsmouth, Portsmouth. Edition: Available editions United Kingdom. Become an author Sign up as a reader Sign in. Roossinck , Penn State. Author Marilyn J.