Portal:Viruses
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".
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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, jaundice and bleeding; death occurs in around a fifth of these cases. Infection otherwise leads to lifelong immunity.
The first recorded outbreak of yellow fever was in Barbados in 1647, and major epidemics have occurred in the Americas, Africa and 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)
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Infectious diseases are symptomatic diseases resulting from the infection and replication of pathogens, including viruses, prions, bacteria, fungi, protozoa and multicellular parasites, in an individual host. Infectious diseases were responsible for over a quarter of human deaths globally in 2002, 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, and the pathogen is generally cleared from the body by the host's immune system. Transmission can occur by physical contact, contaminated food, body fluids, objects, airborne inhalation or via vectors, such as the mosquito (pictured). Diagnosis often involves identifying the pathogen; techniques include culture, microscopy, immunoassays and PCR-based molecular diagnostics.
16 March: Multiple new cases of Ebola virus are reported in Koropara, southern Guinea. WHO
10 March: The ongoing Middle East respiratory syndrome coronavirus outbreak (virus pictured) continues in Saudi Arabia and Qatar, with 46 new cases in February and March. WHO
8 March: Endogenous retrovirus Fc sequences, first identified in primates, are found in 11 different mammalian orders including rodents and carnivores. eLife
4 March: Endogenous retrovirus regulatory elements act as enhancers for interferon-induced immune genes in mammals. Science
4 March: Abnormal foetal ultrasound results are found in 12 of 42 pregnant women infected with Zika virus in Rio de Janeiro. NEJM
4 March: Zika virus is shown to productively infect human neural progenitor cells in vitro, causing cell death. Cell Stem Cell
1 March: The first dengue outbreak in Uruguay is reported, with 17 confirmed cases, mainly in Montevideo. WHO
27 February: The first chikungunya outbreak (virus pictured) in Argentina is reported, with 30 confirmed non-imported cases, mainly in Tartagal. WHO
29 February: A case-control study in 42 people with Guillain–Barré syndrome in Tahiti, French Polynesia in 2013–14 suggests that Zika virus might cause the syndrome. Lancet
24 February: A meta-analysis estimates that 2.3 million people, mainly those who inject drugs, are infected with both HIV and hepatitis C virus (HCV) and 82% of HIV+ injecting drug users are also infected with HCV. Lancet Infect Dis
24 February: In 82 Liberian Ebola survivors participating in the PREVAIL III study, frequent neurological problems are seen at least 6 months after the onset of symptoms. EurekAlert
23 February: Japanese encephalitis virus can be transmitted directly between pigs, without requiring a mosquito vector. Nat Commun
17 February: A novel gammaherpesvirus related to equine herpesvirus 2 is discovered in a cell line derived from the cave myotis bat (pictured). mSphere
16 February: An outbreak of Lassa fever occurs in Benin, with 71 suspected cases including 23 deaths; a Nigerian outbreak is also ongoing. WHO 1, 2 Template:/box-footer
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The West African Ebola epidemic was the most widespread outbreak of the disease to date, and the first to occur outside Sub-Saharan Africa. Beginning in Meliandou in southern Guinea in December 2013, it spread to adjacent Liberia and Sierra Leone, affecting the densely populated cities of Conakry and Monrovia, with minor outbreaks in Mali and Nigeria. The epidemic was under control by late 2015, but occasional cases continue to occur as of March 2016. More than 28,000 suspected cases were reported with more than 11,000 deaths, a case fatality rate of around 58% in hospitalised patients and up to 70% overall. Around 10% of the dead were healthcare workers.
Extreme poverty, a dysfunctional healthcare system, a distrust of government officials after years of armed conflict, local burial customs involving washing the body after death, and a delay in response of several months all contributed to the failure to contain the epidemic.
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| “ | We are part virus. This bizarre yet inescapable fact has been revealed over the past 30 years, as scientists have spelunked their way through the human genome and encountered stretches of DNA with the telltale chemical signatures of viruses. | ” |
Template:/box-header Viruses & Subviral agents: elephant endotheliotropic herpesvirus • HIV • introduction to viruses
• Playa de Oro virus • poliovirus • prion • rotavirus • viruses
Diseases: colony collapse disorder • common cold • dengue fever • gastroenteritis • Guillain–Barré syndrome • hepatitis B • hepatitis C • herpes simplex • HIV/AIDS • influenza • meningitis • poliomyelitis • shingles • smallpox
Epidemiology & Interventions: 1918 flu pandemic • 2007 Bernard Matthews H5N1 outbreak • 2009 flu pandemic • HIV/AIDS in Malawi • polio vaccine
Host response: antibody • immune system • RNA interference
Social & Media: And the Band Played On • Contagion • "Flu Season" • Frank's Cock • Race Against Time • social history of viruses • "Steve Burdick" • "The Time Is Now"
People: Brownie Mary • Frank Macfarlane Burnet • Aniru Conteh • HIV-positive people • people with hepatitis C • poliomyelitis survivors • Ryan White Template:/box-footer
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Alphaviruses are a genus of RNA viruses in the Togaviridae family. The spherical enveloped virion is 70 nm in diameter and contains a single-stranded, positive-sense RNA genome of 11–12 kb. Members of the genus infect humans, horses and other mammals, as well as fish, birds, other vertebrates and invertebrates. Some alphaviruses cause significant disease in humans, with arthritis, encephalitis, rashes and fever being the most frequently observed symptoms.
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. Three subgroups are now known, the Semliki Forest virus (also including o'nyong-nyong, chikungunya and Ross River viruses), eastern equine encephalitis virus (also including Venezuelan equine encephalitis virus (VEEV)) and Sindbis virus groups. Alphaviruses are transmitted by insect vectors, predominantly mosquitoes. Large mammals usually form dead-end hosts for the viruses, although the horse is a major reservoir for VEEV. No human vaccine or antiviral drug has been licensed. Prevention is predominantly by control of the insect vector.
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- ...that Australian pilot and nurse Robin Miller (monument pictured) borrowed money to buy a Cessna 182 and flew to remote outback areas in Western Australia to vaccinate Indigenous Australian children against polio, becoming known as the "Sugarbird Lady"?
- ...that the Mokola virus is a relative of the rabies virus and was first isolated in tree shrews?
- ...that in 1995–97, a Centers for Disease Control program identified over a hundred patients likely suffering from life-threatening infections new in the history of emerging infectious diseases?
- ...that Batheay District in Kampong Cham Province, Cambodia, was the site of an outbreak of the deadly H5N1 virus in 2006?
- ...that Fig Trees, an operatic documentary about AIDS activism, is narrated by a singing albino squirrel?
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Ryan Wayne White (6 December 1971 – 8 April 1990) was an HIV-positive American teenager who became a national spokesman for AIDS research and public education about HIV/AIDS, after being expelled from school because of his infection.
White, a haemophiliac, was diagnosed in 1984 after infection by a contaminated blood treatment. HIV/AIDS was then poorly understood, and his return to school in Kokomo, Indiana was prevented by protesters; the ensuing legal battle gained national media coverage. Before his case, AIDS was widely associated with the male gay community; White was one of several who helped to shift that perception.
White died in 1990, one month before his high school graduation. Shortly afterwards, the U.S. Congress passed a major piece of AIDS legislation, the Ryan White Care Act. Ryan White Programs remain the largest provider of services for people living with HIV/AIDS in the United States.
5 June 1981: First report of HIV/AIDS (symbol pictured) appeared in medical literature
6 June 1997: Gene silencing in plants shown to be a viral defence mechanism
7–13 June 1962: Donald Caspar and Aaron Klug proposed the quasi-equivalence principle of virus structure
7–13 June 1962: André Lwoff proposed a viral classification scheme based on nature of genome, type of symmetry and presence of envelope
7–13 June 1962: George Hirst proposed that the influenza virus genome is segmented
9 June 1981: The American Society for Virology was founded
13 June 2012: First case of Middle East respiratory syndrome coronavirus (MERS-CoV) occurred in Saudi Arabia
18 June 1981: A vaccine against foot-and-mouth disease was the first genetically engineered vaccine
21 June 1996: Nevirapine approved, first NNRTI for HIV/AIDS
26 June 1993: Clinical trial of hepatitis B virus drug fialuridine terminated; the drug caused several fatalities due to lactic acidosis
28 June 2011: FAO declared rinderpest eradicated
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| “ | the most damaging medical hoax of the last 100 years —Dennis Flaherty, 2011 |
” |
The MMR vaccine controversy centered around the – now discredited – notion that the combined vaccine for measles, mumps and rubella (MMR) might be associated with colitis and autism spectrum disorders. The idea was based on a research paper by Andrew Wakefield and co-authors, published in the prestigious medical journal The Lancet in 1998, and subsequently shown to be fraudulent. Sunday Times journalist Brian Deer's investigations revealed that Wakefield had manipulated evidence and had multiple undeclared conflicts of interest. The Lancet paper was retracted in 2010; Wakefield was found guilty of serious professional misconduct by the General Medical Council, and struck off the UK's Medical Register. The claims in Wakefield's article were widely reported in the press, resulting in a sharp drop in vaccination uptake in the UK and Ireland. A significantly increased incidence of measles and mumps followed, leading to deaths and severe injuries. Multiple large epidemiological studies have found no link between the vaccine and autism.
A selection of recent articles of interest include:
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