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 6,000 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
Yellow fever is an acute haemorrhagic fever caused by the yellow fever virus, an RNA virus in the Flaviviridae family. It infects humans, other primates, and Aedes aegypti and other mosquito species, which act as the vector. After transmission by the bite of a female mosquito, the virus replicates in lymph nodes, infecting dendritic cells, and can then spread to liver hepatocytes. Symptoms generally last 3–4 days, and include fever, nausea and muscle pain. In around 15% of people, a toxic phase follows with recurring fever, liver damage and jaundice, sometimes accompanied by bleeding and kidney failure; death occurs in 20–50% of those who develop jaundice. Infection otherwise leads to lifelong immunity.
The first definitive outbreak of yellow fever was in Barbados in 1647, and major epidemics have occurred in the Americas and southern Europe since that date. Yellow fever is endemic in tropical and subtropical areas of South America and Africa; its incidence has been increasing since the 1980s. An estimated 200,000 cases and 30,000 deaths occur each year, with almost 90% of cases being in Africa. Antiviral therapy is not effective. A vaccine is available, and vaccination, mosquito control and bite prevention are the main preventive measures.
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The common cold is the most frequent infectious disease. Despite the advice to "consult your physician" no antiviral treatment has been approved, and colds are only rarely associated with serious complications.
Credit: Federal Art Project (1937)
In the news
26 February: In the ongoing pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), more than 110 million confirmed cases, including 2.5 million deaths, have been documented globally since the outbreak began in December 2019. WHO
18 February: Seven asymptomatic cases of avian influenza A subtype H5N8, the first documented H5N8 cases in humans, are reported in Astrakhan Oblast, Russia, after more than 100,0000 hens died on a poultry farm in December. WHO
14 February: Seven cases of Ebola virus disease are reported in Gouécké, south-east Guinea. WHO
7 February: A case of Ebola virus disease is detected in North Kivu Province of the Democratic Republic of the Congo. WHO
4 February: An outbreak of Rift Valley fever is ongoing in Kenya, with 32 human cases, including 11 deaths, since the outbreak started in November. WHO
21 November: The US Food and Drug Administration (FDA) gives emergency-use authorisation to casirivimab/imdevimab, a combination monoclonal antibody (mAb) therapy for non-hospitalised people twelve years and over with mild-to-moderate COVID-19, after granting emergency-use authorisation to the single mAb bamlanivimab earlier in the month. FDA 1, 2
18 November: The outbreak of Ebola virus disease in Équateur Province, Democratic Republic of the Congo, which started in June, has been declared over; a total of 130 cases were recorded, with 55 deaths. UN
Selected article
Infectious diseases are symptomatic diseases of an individual host resulting from the infection and replication of pathogens, including viruses, prions, bacteria, fungi, protozoa and multicellular parasites. Infectious diseases were responsible for 17% of human deaths globally in 2013, with HIV, measles and influenza being among the most significant viral causes of death.
Infectious pathogens must enter, survive and multiply within the host, and spread to fresh hosts. Relatively few microorganisms cause disease in healthy individuals, and infectious disease results from the interplay between these rare pathogens and the host's defences. Infection does not usually result in the host's death. The pathogen is generally cleared from the body by the host's immune system, although persistent infection occurs with several viruses. Transmission can occur by physical contact, contaminated food, water or objects, body fluids, airborne inhalation or via vectors, such as the mosquito (pictured). Diagnosis sometimes involves identifying the pathogen; techniques include culture, microscopy, immunoassays and PCR-based diagnostics.
Selected outbreak
The last recorded smallpox death occurred during the 1978 smallpox outbreak in Birmingham, UK. The outbreak resulted from accidental exposure to the Abid strain of Variola major, from a laboratory, headed by Henry Bedson, at the University of Birmingham Medical School – also associated with an outbreak in 1966. Bedson was investigating strains of smallpox known as whitepox, considered a potential threat to the smallpox eradication campaign, then in its final stages.
A medical photographer who worked on the floor above the laboratory showed smallpox symptoms in August and died the following month; one of her contacts was also infected but survived. The government inquiry into the outbreak concluded that she had been infected in late July, possibly via ducting, although the precise route of transmission was subsequently challenged. The inquiry criticised the university's safety procedures. Bedson committed suicide while under quarantine. Radical changes in UK research practices for handling dangerous pathogens followed, and all known stocks of smallpox virus were concentrated in two laboratories.
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| “ | To help conceptualize the sheer number of viruses in existence, their current biomass has been estimated to equal that of 75 million blue whales (approximately 200 million tonnes) and, if placed end to end, the collective length of their virions would span 65 galaxies. | ” |
—Peter Simmonds
Recommended articles
Viruses & Subviral agents: bat virome • 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 • polio • pneumonia • shingles • smallpox
Epidemiology & Interventions: 2007 Bernard Matthews H5N1 outbreak • Coalition for Epidemic Preparedness Innovations • Disease X • 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" • "What Lies Below"
People: Brownie Mary • Macfarlane Burnet • Bobbi Campbell • 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
Hantaviruses (or orthohantaviruses) are a family of RNA viruses in the Bunyavirales order. The enveloped virion is 120–160 nm in diameter and contains a single-stranded, negative-sense RNA genome with three segments. They infect many species of rodents, as well as shrews and moles, without causing disease, and can be transmitted to humans, where they can cause serious disease. Hantaan virus, the first known hantavirus, was discovered in 1976 as the cause of a novel haemorrhagic fever affecting combatants in the Korean War; it can also be caused by other hantaviruses, including Dobrava-Belgrade and Seoul viruses. Some hantaviruses, including Sin Nombre and Bayou, cause a pulmonary syndrome. Others have not yet been associated with human disease.
Unlike other bunyaviruses, hantaviruses are not transmitted by arthropods. Rodents act as the vector, with transmission to humans usually occurring via contact with urine, saliva or faeces, by inhalation of aerosolised excreta or by bite. Little is understood about how hantaviruses cause disease; the main site of viral replication in the body is unknown. Rodent control is important in disease prevention.
Did you know?
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- ...that the greenbug (pictured) is the vector of several plant viruses?
- ...that during the West African Ebola virus epidemic as many as 15 different vaccines were in development?
- ...that in 1978, populations of the gulf sea star in the Gulf of California were devastated by starfish wasting disease and had not fully recovered twenty years later?
- ...that virologist Stephen Straus, first head of the National Center for Complementary and Alternative Medicine, said he did not use alternative medicine?
- ...that Looking for Madonna, meant to raise awareness of HIV/AIDS in Papua, used shots of a green bra to symbolise sex?
Selected biography
Randy Shilts (8 August 1951 – 17 February 1994) was an American journalist, author and AIDS activist. The first openly gay reporter for a mainstream US newspaper, Shilts covered the unfolding story of AIDS and its medical, social, and political ramifications from the first reports of the disease in 1981. New York University's journalism department later ranked his 1981–85 AIDS reporting in the top fifty works of American journalism of the 20th century. His extensively researched account of the early days of the epidemic in the US, And the Band Played On Politics, People, and the AIDS Epidemic, first published in 1987, brought him national fame. The book won the Stonewall Book Award and was made into an award-winning film. Shilts saw himself as a literary journalist in the tradition of Truman Capote and Norman Mailer. His writing has a powerful narrative drive and interweaves personal stories with political and social reporting.
He received the 1988 Outstanding Author award from the American Society of Journalists and Authors, the 1990 Mather Lectureship at Harvard University, and the 1993 Lifetime Achievement Award from the National Lesbian and Gay Journalists' Association. He died of AIDS in 1994.
In this month
1 July 1796: Edward Jenner first challenged James Phipps with variolation, showing that cowpox inoculation is protective against smallpox
3 July 1980: Structure of southern bean mosaic virus solved by Michael Rossmann and colleagues
6 July 1885: Louis Pasteur (pictured) gave rabies vaccine to Joseph Meister
10 July 1797: Jenner submitted paper on Phipps and other cases to the Royal Society; it was read to the society but not published
14–20 July 1968: First International Congress for Virology held in Helsinki
16 July 2012: FDA approved tenofovir/emtricitabine (Truvada) for prophylactic use against HIV; first prophylactic antiretroviral
19 July 2013: Pandoravirus described, with a genome twice as large as Megavirus
22 July 1966: International Committee on Nomenclature of Viruses (later the ICTV) founded
25 July 1985: Film star Rock Hudson made his AIDS diagnosis public, increasing public awareness of the disease
28 July 2010: First global World Hepatitis Day
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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