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
Hepatitis B is an infectious inflammatory disease of the liver caused by the hepatitis B virus (HBV), a hepadnavirus. It affects humans and possibly other great apes. The virus is transmitted by exposure to infectious blood or some body fluids. Mother-to-child transmission is a major route in endemic countries. HBV is 50–100 times more infectious than HIV. The virus replicates in liver cells, and enters the blood where viral proteins and antiviral antibodies are found.
Acute infection is often asymptomatic but can cause liver inflammation resulting in vomiting, jaundice and, rarely, death. Over 95% of infected adults and older children clear the infection spontaneously, developing protective immunity. Only 30% of children aged 1–6 years and 5% of newborns infected perinatally clear the infection. Chronic hepatitis B may eventually progress to cirrhosis and liver cancer, causing death in around 40% of those chronically infected. The virus has infected humans since at least the Bronze Age, with HBV DNA being found in 4,500-year-old human remains. About a third of the global population has been infected at one point in their lives, including nearly 350 million who are chronic carriers. The virus is endemic in East Asia and sub-Saharan Africa. Infection can be prevented by vaccination.
Selected image
Respiratory failure in bulbar and bulbospinal polio condemned many patients to one or two weeks in an "iron lung" or negative-pressure ventilator. The first ventilator designed for polio patients appeared in 1918; this model dates from the 1950s.
Credit: Hewa (December 2011)
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
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Bats host a diverse array of viruses, including all seven types described by the Baltimore classification system. The most common viruses known to infect bats are coronaviruses. Bats harbour many viruses that are zoonotic, or capable of infecting humans, including rabies virus, SARS-CoV, SARS-CoV-2, MERS-CoV, Nipah virus, Hendra virus and Marburg virus (hosted by the Egyptian fruit bat; pictured), and some bat-borne viruses are considered important emerging viruses. Bats may also play a role in the ecology of the Ebola virus. Most zoonotic bat viruses are transmitted by direct contact with infected bat fluids such as urine, guano and saliva, or through contact with an infected intermediate host; transmission of rabies from bats to humans usually occurs via biting. Butchering or consuming bat meat could potentially lead to viral transmission.
Bats rarely become ill from viral infections, and rabies is the only viral disease known to kill them. They might be more tolerant of infection than other mammals. Their immune systems differ from those of other mammals in their lack of several inflammasomes, which activate the body's inflammatory response, as well as a dampened stimulator of interferon genes response, which helps to control the host response to pathogens.
Selected outbreak
The 2001 foot-and-mouth outbreak included 2,000 cases of the disease in cattle and sheep across the UK. The source was a Northumberland farm where pigs had been fed infected meat that had not been adequately sterilised. The initial cases were reported in February. The disease was concentrated in western and northern England, southern Scotland and Wales, with Cumbria being the worst-affected area. A small outbreak occurred in the Netherlands, and there were a few cases elsewhere in Europe.
The UK outbreak was controlled by the beginning of October. Control measures included stopping livestock movement and slaughtering over 6 million cows and sheep. Public access to farmland and moorland was also restricted (pictured), greatly reducing tourism in affected areas, particularly in the Lake District. Vaccination was used in the Netherlands, but not in the UK due to concerns that vaccinated livestock could not be exported. The outbreak cost an estimated £8 billion in the UK.
Selected quotation
| “ | A virus is a piece of bad news wrapped in protein. | ” |
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
Epstein–Barr virus (EBV) (also human herpesvirus 4) is a DNA virus in the Herpesviridae family which infects humans. The virion is around 122–180 nm in diameter. As in all herpesviruses, the nucleocapsid is surrounded by a protein tegument, as well as an envelope. The double-stranded DNA genome is about 172 kb, with 85 genes, making it one of the more complex viruses.
Transmission is via saliva and genital secretions. The virus infects epithelial cells in the pharynx and B cells of the immune system, producing virions by budding. EBV also becomes latent in B cells, possibly in the bone marrow, allowing the infection to persist lifelong. In the latent state, the linear genome is made circular and replicates in the nucleus separately from the host DNA as an episome. Reactivation is poorly understood but is thought to be triggered by the B cell responding to other infections. EBV infection occurs in around 95% of people. Infectious mononucleosis or glandular fever can occur when first infection is delayed until adolescence or adulthood. EBV is associated with some types of cancer, including Burkitt's lymphoma and nasopharyngeal carcinoma. In people with HIV, it can cause hairy leukoplakia and central nervous system lymphomas.
Did you know?
- ...that flow cytometry bioinformaticians use methods from computational statistics and machine learning to analyse single cell data gathered by flow cytometry for cancer and HIV/AIDS research (output pictured)?
- ...that Sierra Leonean physician Aniru Conteh saved thousands of lives from Lassa fever before dying from the disease himself?
- ...that early in the history of veterinary medicine in the Philippines, a cattle plague killed 600,000 animals from 1901 to 1902 alone?
- ...that the isolation of antibodies and flu viruses from birds on Tryon Island, a coral cay off the coast of Queensland, Australia, led to the development of antiviral drugs, such as oseltamivir?
- ...that the Plague of Athens devastated ancient Athens in 430 BC, perhaps leading ultimately to the city's defeat in the Peloponnesian War?
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
6 October 2008: Nobel Prize in Physiology or Medicine awarded to Harald zur Hausen for showing that human papillomaviruses cause cervical cancer, and to Françoise Barré-Sinoussi and Luc Montagnier for discovering HIV
7 October 2005: 1918 Spanish influenza pandemic strain reconstituted
9 October 1991: Didanosine was the second drug approved for HIV/AIDS
12 October 1928: First use of an iron lung in a poliomyelitis patient
12 October 2007: Raltegravir (pictured) approved; first HIV integrase inhibitor
14 October 1977: Habiba Nur Ali was the last person to die from naturally occurring smallpox
14 October 2010: Rinderpest eradication efforts announced as stopping by the UN
16 October 1975: Last known case of naturally occurring Variola major smallpox reported
25 October 2012: Alipogene tiparvovec, a gene therapy for lipoprotein lipase deficiency using an adeno-associated virus-based vector, was the first gene therapy to be licensed
26 October 1977: Ali Maow Maalin developed smallpox rash; the last known case of naturally occurring Variola minor smallpox
26 October 1979: Smallpox eradication in the Horn of Africa formally declared by WHO, with informal declaration of global eradication
27 October 2015: Talimogene laherparepvec was the first oncolytic virus to be approved by the FDA to treat cancer
Selected intervention
Zidovudine (ZDV) (also known as AZT and sold as Retrovir) is an antiretroviral drug used in the prevention and treatment of HIV/AIDS. Classed as a nucleoside analogue reverse-transcriptase inhibitor, it inhibits HIV's reverse transcriptase enzyme, which copies the viral RNA into DNA and is essential for its replication. The first breakthrough in AIDS therapy, ZDV was licensed in 1987. While it significantly reduces HIV replication, leading to some clinical and immunological benefits, when used alone ZDV does not completely stop replication, allowing the virus to become resistant to it. The drug is therefore used together with other anti-HIV drugs in combination therapy called highly active antiretroviral therapy. To simplify its administration, ZDV is included in combination pills with lamivudine (Combivir) and lamivudine plus abacavir (Trizivir). ZDV continues to be used to prevent HIV transmission from mother to child during childbirth; it was previously part of the standard post-exposure prophylaxis after needlestick injury.
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