Portal:Viruses
The Viruses Portal
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Viruses are small infectious agents that can replicate only inside the living cells of an organism. Viruses infect all forms of life, including animals, plants, fungi, bacteria and archaea. They are found in almost every ecosystem on Earth and are the most abundant type of biological entity, with millions of different types, although only about 5,000 viruses have been described in detail. Some viruses cause disease in humans, and others are responsible for economically important diseases of livestock and crops.
Virus particles (known as virions) consist of genetic material, which can be either DNA or RNA, wrapped in a protein coat called the capsid; some viruses also have an outer lipid envelope. The capsid can take simple helical or icosahedral forms, or more complex structures. The average virus is about 1/100 the size of the average bacterium, and most are too small to be seen directly with an optical microscope.
The origins of viruses are unclear: some may have evolved from plasmids, others from bacteria. Viruses are sometimes considered to be a life form, because they carry genetic material, reproduce and evolve through natural selection. However they lack key characteristics (such as cell structure) that are generally considered necessary to count as life. Because they possess some but not all such qualities, viruses have been described as "organisms at the edge of life".
Selected disease
Influenza, or flu, is an infectious disease caused by some orthomyxoviruses, that affects birds and some mammals including humans, horses and pigs. Influenza is predominantly transmitted through the air by coughs or sneezes, creating aerosols containing the virus. It can also be transmitted by contact with bird droppings or nasal secretions, or by touching contaminated surfaces. As the virus can be inactivated by soap, frequent hand washing reduces the risk of infection. Around a third of cases show no symptoms. The most common symptoms include fever, runny nose, sore throat, muscle pains, headache, cough and fatigue. Influenza is occasionally associated with nausea and vomiting, particularly in children. Pneumonia is a rare complication which can be life-threatening.
Influenza spreads around the world in seasonal epidemics, resulting in about 3–5 million cases of severe illness annually, and about 250,000–500,000 deaths, mainly in the young, the old and those with other health problems. Annual influenza vaccinations are recommended for those at high risk. Sporadic influenza pandemics have been recorded since at least the 16th century. The Spanish flu pandemic of 1918–20 is estimated to have killed 50–100 million people.
Selected image
ΦX174 is a bacteriophage whose DNA genome size of 5386 nucleotides, among the smallest of DNA viruses, has led to it being the subject of pioneering research in molecular biology.
Credit: Fdardel (21 March 2009)
In the news
4 April: The ongoing pandemic of a novel coronavirus is accelerating rapidly; more than a million confirmed cases, including more than 57,000 deaths, have been documented globally since the outbreak began in December 2019. WHO 1, 2
27 March: An international, randomised, non-blinded, clinical trial organised by the World Health Organization of four potential treatments for COVID-19 – remdesivir; chloroquine or hydroxychloroquine; lopinavir/ritonavir; or lopinavir/ritonavir plus interferon-beta – is about to start enrolling patients. Science, WHO
16 March: A phase I clinical trial of a messenger RNA-based vaccine candidate for the novel coronavirus begins in Seattle. NIH
11 March: The World Health Organization describes the ongoing outbreak of respiratory disease caused by a novel coronavirus as a pandemic. WHO
10 March: A patient with apparent clearance of HIV after stem-cell therapy continues to have no viable virus detectable in blood or other reservoirs after 30 months without antiretroviral treatment. Lancet
9 March: No new cases have been recorded in three weeks in the ongoing Ebola virus outbreak in the North Kivu and Ituri provinces of the Democratic Republic of the Congo; as of 3 March there had been a total of 3444 cases, including 2264 deaths, since the outbreak began in August 2018. WHO 1, 2
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12 February: The ongoing Ebola virus outbreak in the North Kivu and Ituri provinces of the Democratic Republic of the Congo remains a Public Health Emergency of International Concern, according to the World Health Organization. WHO 1
7 February: Chinese scientists announce that novel coronavirus (2019-nCoV) is 99% identical to a coronavirus isolated from pangolins, suggesting these animals might be an intermediate host. Nature
5 February: A study of 2658 samples from 38 different types of cancer found that 16% were associated with a virus, higher than previous estimates, but did not identify any new candidate tumour viruses. Nat Genet
4 February: Over 2500 putative circular DNA virus genomes are catalogued from metagenomic surveys of human and animal samples, including over 600 dissimilar to existing virus groups. eLife, Science
3 February: The US National Institute of Allergy and Infectious Diseases stops the South African HVTN 702 Phase IIb/III clinical trial of an investigational HIV vaccine early, after the vaccine failed to prevent HIV infection. NIH
Selected article
A global drive to eradicate poliovirus started in 1988, when there were an estimated 350,000 cases of wild poliovirus infection globally. Two diseases, both caused by viruses, have been eradicated, smallpox in 1980 and rinderpest in 2011. Poliovirus only infects humans. It persists in the environment for a few weeks at room temperature and a few months at 0–8 °C. The oral polio vaccine is inexpensive, highly effective and is predicted to generate lifelong immunity. Reversion of live vaccine strains to virulence has resulted in occasional cases of vaccine-associated paralysis.
Annual reported cases of wild poliovirus infection fell to a low of 22 in 2017, but rose to 33 in 2018. As of 2019, the wild virus remains endemic in three countries: Afghanistan, Pakistan and Nigeria. Vaccine-derived poliovirus is also circulating in several countries. A lack of basic health infrastructure and civil war remain significant obstacles to eradication. Some local communities have opposed immunisation campaigns, and vaccination workers have been murdered in Pakistan and Nigeria.
Selected outbreak
The West African Ebola epidemic was the most widespread outbreak of the disease to date. Beginning in Meliandou in southern Guinea in December 2013, it spread to adjacent Liberia and Sierra Leone, affecting the cities of Conakry and Monrovia, with minor outbreaks in Mali and Nigeria. Cases reached a peak in October 2014 and the epidemic was under control by late 2015, although occasional cases continued to occur into April 2016. Ring vaccination with the then-experimental vaccine rVSV-ZEBOV was trialled in Guinea.
More than 28,000 suspected cases were reported with more than 11,000 deaths; the case fatality rate was around 40% overall and around 58% in hospitalised patients. Early in the epidemic nearly 10% of the dead were healthcare workers. The outbreak left about 17,000 survivors, many of whom reported long-lasting post-recovery symptoms. Extreme poverty, dysfunctional healthcare systems, distrust of government after years of armed conflict, local burial customs of washing the body, the unprecedented spread of Ebola to densely populated cities, and the delay in response of several months all contributed to the failure to control the epidemic.
Selected quotation
| “ | A virus is a piece of bad news wrapped in protein. | ” |
Recommended articles
Viruses & Subviral agents: elephant endotheliotropic herpesvirus • HIV • introduction to viruses
• Playa de Oro virus • poliovirus • prion • rotavirus • virus
Diseases: colony collapse disorder • common cold • croup • dengue fever • gastroenteritis • Guillain–Barré syndrome • hepatitis B • hepatitis C • hepatitis E • herpes simplex • HIV/AIDS • influenza • meningitis • myxomatosis • poliomyelitis • pneumonia • shingles • smallpox
Epidemiology & Interventions: 2007 Bernard Matthews H5N1 outbreak • 2009 flu pandemic • HIV/AIDS in Malawi • polio vaccine • Spanish flu • West African Ebola virus epidemic
Virus–Host interactions: antibody • host • immune system • parasitism • RNA interference
Methodology: metagenomics
Social & Media: And the Band Played On • Contagion • "Flu Season" • Frank's Cock • Race Against Time: Searching for Hope in AIDS-Ravaged Africa • social history of viruses • "Steve Burdick" • "The Time Is Now"
People: Brownie Mary • Macfarlane Burnet • Aniru Conteh • people with hepatitis C • HIV-positive people • Bette Korber • Henrietta Lacks • Linda Laubenstein • Barbara McClintock • poliomyelitis survivors • Joseph Sonnabend • Eli Todd • Ryan White
Selected virus
Poliovirus is an enterovirus, an RNA virus in the Picornaviridae family, associated with the paralytic disease polio. The icosahedral virus particle is about 30 nanometres in diameter and lacks an envelope. It contains a relatively short, single-stranded positive RNA genome of around 7500 nucleotides, which encodes about ten viral products. The virus has a fairly high mutation rate even for an RNA virus. Historically there were three serotypes, each with a slightly different capsid protein; PV1 is the most common, and PV2 was declared eradicated in 2015.
The virus only naturally infects humans, although some monkeys can be infected experimentally; 95% of infections are asymptomatic. Infection occurs via the faecal–oral route and viral replication occurs in the alimentary tract. The virus enters the host cell by binding to an immunoglobulin-like receptor, CD155. Fully assembled poliovirus leaves the cell 4–6 hours after initiation of infection. Poliovirus was first isolated in 1909 by Karl Landsteiner and Erwin Popper. Its genome was sequenced in 1981. Among the simplest clinically significant viruses, poliovirus is one of the best-characterised viruses, and has become a useful model for studying RNA viruses.
Did you know?
- ...that agnoprotein (pictured) is found in two polyomaviruses that can cause human disease, JC virus and BK virus?
- ...that the immunology professor Mary Collins studies ways to use genetically engineered HIV as a vaccine?
- ...that the Alternanthera mosaic virus, a type of Potexvirus, has been misdiagnosed as the closely related Papaya mosaic virus?
- ...that though once thought to be sterile, the uterine microbiome contains at least 14 commensal microorganisms in healthy women?
- ...that a form of encephalitis that killed three people is believed to have been caused by a virus carried by their pet variegated squirrels?
Selected biography
Peter Piot (born 17 February 1949) is a Belgian virologist and public health specialist, known for his work on Ebola virus and HIV.
During the first outbreak of Ebola in Yambuku, Zaire in 1976, Piot was one of a team that discovered the filovirus in a blood sample. He and his colleagues travelled to Zaire to help to control the outbreak, and showed that the virus is transmitted via blood and during preparation of bodies for burial. He advised WHO during the West African Ebola epidemic of 2014–16.
In the 1980s, Piot participated in collaborative projects in Burundi, Côte d'Ivoire, Kenya, Tanzania and Zaire, including Project SIDA in Kinshasa, the first international project on AIDS in Africa, which provided the foundations for understanding HIV infection in that continent. He was the founding director of UNAIDS, and has served as president of the International AIDS Society and assistant director of the WHO Global HIV/AIDS Programme. As of 2020, he directs the London School of Hygiene & Tropical Medicine.
In this month
1 September 1910: Peyton Rous shows that a sarcoma of chickens, subsequently associated with Rous sarcoma virus, is transmissible
3 September 1917: Discovery of bacteriophage of Shigella by Félix d'Herelle
8 September 1976: Death of Mabalo Lokela, the first known case of Ebola virus
8 September 2015: Discovery of giant virus Mollivirus sibericum in Siberian permafrost
11 September 1978: Janet Parker was the last person to die of smallpox
12 September 1957: Interferon discovered by Alick Isaacs and Jean Lindenmann
12 September 1985: Structure of human rhinovirus 14 (pictured) solved by Michael Rossmann and colleagues, the first atomic-level structure of an animal virus
17 September 1999: Jesse Gelsinger died in a clinical trial of gene therapy using an adenovirus vector, the first known death due to gene therapy
20 September 2015: Wild poliovirus type 2 declared eradicated
26 September 1997: Combivir (zidovudine/lamivudine) approved; first combination antiretroviral
27 September 1985: Structure of poliovirus solved by Jim Hogle and colleagues
28 September 2007: First World Rabies Day is held
Selected intervention
Ribavirin is a nucleoside analogue that mimics the nucleoside guanosine. It shows some activity against a broad range of DNA and RNA viruses, but is less effective against dengue fever, yellow fever and other flaviviruses. The drug was first synthesised in the early 1970s by Joseph T. Witkowski and Roland K. Robins. Ribavirin's main current use is against hepatitis C, in combination with pegylated interferon, nucleotide analogues and protease inhibitors. It has been used in the past in an aerosol formulation against respiratory syncytial virus-related diseases in children. Ribavirin has been used in combination as part of an experimental treatment for rabies. It is also the only available treatment for the viruses causing some viral haemorrhagic fevers, including Lassa fever, Crimean–Congo haemorrhagic fever and hantavirus disease, but is ineffective against the filovirus diseases, Ebola and Marburg. Clinical use is limited by the drug building up in red blood cells to cause haemolytic anaemia.
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