Discovering an invisible pathogen
In 1892 the Russian botanist Dmitri Ivanovsky found that sap from tobacco plants with mosaic disease stayed infectious even after passing through porcelain filters that trapped bacteria. In 1898 the Dutch microbiologist Martinus Beijerinck concluded it was not a bacterium but a "contagious living fluid" and called it a virus, Latin for poison. That same year Loeffler and Frosch showed that foot-and-mouth disease was also caused by a filterable agent. Frederick Twort (1915) and Félix d'Hérelle (1917) discovered bacteriophages, viruses that infect bacteria, and in 1935 Wendell Stanley crystallised tobacco mosaic virus, sharing the 1946 Nobel Prize in Chemistry. Only with the electron microscope in the late 1930s did anyone see a virus.
Structure and replication
A virus consists of a DNA or RNA genome wrapped in a protein shell called a capsid; some, such as influenza and coronaviruses, also have a lipid envelope. Viruses cannot make energy or proteins on their own: they bind receptors on a host cell, enter, and commandeer its machinery to make thousands of copies. In 1952 Alfred Hershey and Martha Chase used phages to show that genetic information is carried by DNA, not protein. In 1971 David Baltimore sorted viruses into seven groups by genome type and replication strategy. RNA viruses make many copying errors and mutate quickly, which is why flu vaccines are updated every year. About 8% of the human genome is the remnant of ancient retroviral infections.
Disease, treatment and whether viruses are alive
Colds, flu, measles, COVID-19, norovirus gastroenteritis, hepatitis, HPV-related cervical cancer and AIDS are all caused by viruses. Françoise Barré-Sinoussi and Luc Montagnier isolated HIV in 1983 (Nobel Prize 2008), and antiretroviral therapy has since turned AIDS into a manageable chronic condition. Antibiotics do not work on viruses; antiviral drugs such as oseltamivir or nirmatrelvir–ritonavir, and vaccines, are the main tools. A millilitre of seawater holds around ten million viruses, most of which never touch humans but regulate microbial ecosystems. Because they lack cells and cannot metabolise or reproduce alone, viruses remain at the centre of a debate over the boundary between living and non-living.
This article is general health information and is not a substitute for diagnosis or treatment. If symptoms persist, see a doctor.
FAQ
- Will antibiotics help me get over a cold faster?
- No. Colds are almost always viral, so antibiotics do nothing except risk side effects and resistance. Doctors prescribe them only if a bacterial complication is suspected.
- How long do viruses survive outside the body?
- It varies. Enveloped viruses such as flu last hours to about a day on surfaces, while non-enveloped viruses such as norovirus can survive for weeks and resist alcohol sanitisers.
Sources reviewed: 2026-10-26
References
- Ivanovsky, D. (1892). Über die Mosaikkrankheit der Tabakspflanze. St. Petersburg Academy of Sciences Bulletin, 35, 67–70.
- Beijerinck, M. W. (1898). Über ein Contagium vivum fluidum als Ursache der Fleckenkrankheit der Tabaksblätter. Verhandelingen der Koninklijke Akademie van Wetenschappen te Amsterdam, 65, 3–21.
- Twort, F. W. (1915). An investigation on the nature of ultra-microscopic viruses. The Lancet, 186(4814), 1241–1243.
- d'Hérelle, F. (1917). Sur un microbe invisible antagoniste des bacilles dysentériques. Comptes Rendus de l'Académie des Sciences, 165, 373–375.
- Stanley, W. M. (1935). Isolation of a crystalline protein possessing the properties of tobacco-mosaic virus. Science, 81(2113), 644–645.
- Hershey, A. D., & Chase, M. (1952). Independent functions of viral protein and nucleic acid in growth of bacteriophage. Journal of General Physiology, 36(1), 39–56.
- Baltimore, D. (1971). Expression of animal virus genomes. Bacteriological Reviews, 35(3), 235–241.
- Barré-Sinoussi, F., et al. (1983). Isolation of a T-lymphotropic retrovirus from a patient at risk for acquired immune deficiency syndrome (AIDS). Science, 220(4599), 868–871.
- Suttle, C. A. (2005). Viruses in the sea. Nature, 437(7057), 356–361.
- Lander, E. S., et al. (2001). Initial sequencing and analysis of the human genome. Nature, 409(6822), 860–921.