What are viruses?
Viruses are present in animals, plants, and other living organisms – and many cause diseases. They are microorganisms that are smaller than bacteria; usually about 20-400 nm, and can be visualised by an electron microscope.
Viruses cannot grow or reproduce without the help of a separate living cell. This is because although viruses have genes, they do not have a cellular structure to perform their own metabolism, thus requiring a host cell to make new products. Therefore viruses attach themselves inside healthy cells once they get inside your body; and use the cell’s nucleus to reproduce themselves.
How are viruses treated?
Many viruses do not need treatment. Your immune systems deals with them and you get better. Vaccines can prevent you getting viruses. Antiviral drugs can be used to treat some viruses but have no effect on bacteria. Antibiotics have no effect on viruses.
Examples of viruses (and infections they cause)
Epstein-Barr virus (EBV). Causes infectious mononucleosis (or ‘glandular fever’ or ‘kissing disease’). The main symptoms include extreme tiredness, swollen glands in the neck and a high temperature. Glandular fever usually gets better by itself.
Hepatitis A,B, C, D and E. Viral hepatitis – is an infection that causes liver inflammation and damage.
Herpes simplex virus (HSV). ‘Cold sores’; Encephalitis – is an inflammation of the brain, usually caused by a viral infection. It’s a rare but serious condition.
Human immunodeficiency virus (HIV). Acquired immunodeficiency syndrome (AIDS) is a long-term condition caused by this virus.
Human papillomavirus (HPV). This is a common sexually transmitted disease (STD) and can cause certain cancers (e.g. cervical) and genital warts.
Influenza viruses. One of causes of influenza (‘flu’). The symptoms of flu are similar to a very bad cold. They include a high temperature, an aching body, tiredness and a headache.
Measles morbillivirus (MeV; also called measles virus, MV) – causes measles. The main symptom is a red-brown blotchy rash. It usually gets better of its own accord. But it can be serious in some people.
Paramyxovirus. Mumps – an infection that causes painful swellings in the sides of your face, and a tender swollen jaw. It usually gets better on its own, but can make some people very ill.
Poliovirus. Poliomyelitis. This virus can infect the spinal cord, causing inability to move parts of the body (paralysis) and in some cases can become life threatening.
Rabies lyssavirus. Rabies – is a rare but very serious infection of the brain and nerves. It’s usually caught from the bite or scratch of an infected animal, most often a dog
Respiratory syncytial virus (RSV). For most adults and healthy children, RSV infection causes symptoms similar to those of a cold.
Rhinoviruses. They are the most common viral infectious agent in humans; and are the predominant cause of the common cold.
Severe acute respiratory syndrome coronavirus 2 (or SARS-CoV-2). This is the cause of COVID-19.
Varicella zoster virus (VZV). Chickenpox (also known as ‘varicella’) and shingles are highly contagious diseases caused by VSV.
Variola virus. Smallpox. Before smallpox was eradicated, it was a serious infectious disease. People who had smallpox had a fever and a distinctive, progressive skin rash.
Other resources
More information on viruses on this US website here.
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Bacteria
Differences between viruses and bacteria.
