Portal:Viruses
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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".
Myxomatosis is a disease of rabbits caused by Myxoma virus, a poxvirus in the genus Leporipoxvirus. The natural hosts are brush rabbits (Sylvilagus bachmani) in North America and tapeti (S. brasiliensis) in South and Central America, in which the myxoma virus causes only a mild disease, involving skin nodules. In European rabbits (Oryctolagus cuniculus), it causes a severe, often fatal, disease. Symptoms include fever, swelling of the eyelids and anogenital area, a mucopurulent ocular and nasal discharge, respiratory distress and hypothermia. Death generally occurs 10–12 days after infection. Myxoma virus is transmitted passively (without replication) by arthropod vectors, usually via the bites of mosquitoes and fleas, and also mites, flies and lice. It can also be transmitted by direct contact, and is shed in the ocular and nasal discharge and from eroded skin.
Myxoma virus was intentionally introduced in Australia, France and Chile in the 1950s to control wild European rabbit populations. This resulted in short-term 10–100-fold reductions in the rabbit population, followed by its recovery with the emergence of myxomatosis-resistant animals and attenuated virus variants. The introduction of myxomatosis is regarded as a classical example of host–pathogen coevolution following cross-species transmission of a pathogen to a naive host.
Culex species mosquitoes transmit West Nile virus. Elimination of the stagnant water pools where the mosquitoes breed, together with other mosquito control measures, is key to preventing disease.
Credit: James Gathany (28 February 2006)
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
The Hershey–Chase experiments were conducted by Alfred Hershey and Martha Chase in 1952 using the T2 bacteriophage (pictured), which is composed of DNA wrapped in a protein shell. Hershey and Chase labelled either the phage DNA using radioactive phosphorus-32 or the protein using radioactive sulphur-35. They allowed the radiolabelled phages to infect unlabelled bacteria, and then agitated in a blender and centrifuged to separate material remaining outside the bacterial cells. The majority of the 32P-labelled DNA entered the host bacterial cell, while all the 35S-labelled protein remained outside. Hershey and Chase also showed that the phage DNA is inserted into the bacteria shortly after the virus attaches to its host.
DNA had been known since 1869, but in 1952 many scientists believed that proteins carried the information for inheritance. Proteins appeared more complex, while DNA was thought to be an inert molecule used for phosphorus storage. These experiments built on earlier research on transformation in bacteria and helped to confirm that DNA, not protein, was the genetic material. Hershey shared the 1969 Nobel Prize in Physiology or Medicine for the research.
The 1918–20 influenza pandemic, the first of the two involving H1N1 influenza virus, was unusually deadly. It infected 500 million people across the entire globe, with a death toll of 50–100 million (3–5% of the world's population), making it one of the deadliest natural disasters of human history. It has also been implicated in the outbreak of encephalitis lethargica in the 1920s. Despite the nickname "Spanish flu", the pandemic's geographic origin is unknown.
Most influenza outbreaks disproportionately kill young, elderly or already weakened patients; in contrast this predominantly killed healthy young adults. Contemporary medical reports suggest that malnourishment, overcrowded medical facilities and poor hygiene promoted fatal bacterial pneumonia. Some research suggests that the virus might have killed through a cytokine storm, an overreaction of the body's immune system. This would mean the strong immune reactions of young adults resulted in a more severe disease than the weaker immune systems of children and older adults.
| “ | ...classical approaches to classification are not suitable for viruses, as rigid hierarchies cannot be imposed on organisms that appear – evolutionarily speaking – to have been rather promiscuous in sharing their characteristics around. | ” |
—Ed Rybicki
Viruses & Subviral agents: bat virome • elephant endotheliotropic herpesvirus • HIV • introduction to viruses
Diseases: colony collapse disorder • common cold • croup • dengue fever
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
Methodology: metagenomics
Social & Media: And the Band Played On • Contagion • "Flu Season" • Frank's Cock
People: Brownie Mary • Macfarlane Burnet
Alphaviruses are a genus of RNA viruses in the Togaviridae family. The spherical enveloped virion is 70 nm in diameter, with a nucleocapsid of 40 nm. It has a single-stranded, positive-sense RNA genome of 11–12 kb. The genus contains more than thirty species, which infect humans, horses, rodents and other mammals, as well as fish, birds, other vertebrates and invertebrates. Alphaviruses are generally transmitted by insect vectors, predominantly mosquitoes, and are an example of arboviruses (arthropod-borne viruses).
The first alphavirus to be discovered was western equine encephalitis virus, by Karl Friedrich Meyer in 1930, in horses with fatal encephalitis in San Joaquin Valley, California, USA. Some members of the genus cause significant disease in humans, including the chikungunya, o'nyong'nyong, Ross River, Sindbis, Barmah Forest and Semliki Forest (pictured) viruses and the eastern, western and Venezuelan equine encephalitis viruses. Arthritis, encephalitis, rashes and fever are the most frequently observed symptoms. Large mammals such as humans usually form dead-end hosts for the viruses, although Venezuelan equine encephalitis virus is mainly amplified in the horse. No human vaccine or antiviral drug has been licensed. Prevention is predominantly by control of the insect vector.
- ...that the p19 protein (dimer pictured) evolved in an arms race between plants and viruses?
- ...that HPgV-2 is the second human Pegivirus ever discovered?
- ...that humans and horses are dead-end hosts for the West Nile virus?
- ...that David A. Cooper diagnosed the first case of HIV in Australia?
- ...that there is indirect, but unconfirmed, evidence of certain diseases being spread by toilet plume?
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.
7 November 1991: Magic Johnson announced his retirement from basketball because of his infection with HIV
14 November 1957: Kuru, the first human prion disease, described by Daniel Gajdusek and Vincent Zigas
16 November 2002: The first case of severe acute respiratory syndrome (virus pictured) recorded in Guangdong, China
17 November 1995: Lamivudine approved for treatment of HIV
22 November 2013: Simeprevir approved for treatment of chronic hepatitis C virus infection
23 November 1978: Structure of tomato bushy stunt virus solved by Stephen Harrison and colleagues, the first atomic-level structure of a virus
24 November 2007: Outbreak of new Ebola species, Bundibugyo virus
26 November 1898: Martinus Beijerinck coined the term contagium vivum fluidum to describe the agent causing tobacco mosaic disease
Several human papillomavirus (HPV) vaccines, including Cervarix and Gardasil, have been approved to protect against infections with particular types of HPV, associated with cervical and other cancers. All vaccines protect against the high-risk HPV types 16 and 18. Gardasil is a quadrivalent vaccine that additionally protects against low-risk HPV-6 and -11, which are associated with most cases of genital warts. A second-generation nine-valent Gardasil vaccine protects against five additional high-risk HPV types. It is estimated that the vaccines may prevent 70% of cervical cancer, 80% of anal cancer, 60% of vaginal cancer, 40% of vulvar cancer and possibly some oropharyngeal cancers. Protection lasts for at least 8–9 years. Some advocate giving Gardasil to men and boys with the primary aim of protecting their female sexual partners; others consider vaccinating only women and girls to be more cost effective. The licensed vaccines are subunit vaccines, containing only the L1 capsid protein of the virus, which self-assembles into virus-like particles. They are not effective in people already infected with HPV. Research is ongoing into therapeutic HPV vaccines including the viral oncoproteins, E6 and E7, but none has yet been licensed.
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