Portal:Viruses

Foot-and-mouth disease or FMD is an economically important disease of even-toed ungulates (cloven-hoofed animals) and some other mammals caused by the FMD virus, a picornavirus. Hosts include cattle, water buffalo, sheep, goats, pigs, antelope, deer and bison; human infection is extremely rare. After a 1–12-day incubation, animals develop high fever, and then blisters inside the mouth (pictured) and on the hooves, which can rupture and cause lameness. Weight loss and reduction in milk production are other possible long-term consequences. Mortality in adult animals is low (2–5%). The virus is highly infectious, with transmission occurring via direct contact, aerosols, semen, consumption of infected food scraps or feed supplements, and via inanimate objects including fodder, farming equipment, vehicles, standing water, and the clothes and skin of humans. Some infected ruminants can transmit infection as asymptomatic carriers.

Friedrich Loeffler showed the disease to be viral in 1897. FMD was widely distributed in 1945. By 2014, North America, Australia, New Zealand, much of Europe, and some South American countries were free of the disease. Major outbreaks include one in the UK in 2001 that cost an estimated £8 billion. The virus is highly variable, with seven serotypes. A vaccine is available, but protection is temporary and strain specific. Other control methods include monitoring programmes, trade restrictions, quarantine, and the slaughter of infected and healthy at-risk animals.

Some viruses, such as the T7 bacteriophage, encode their own RNA polymerase, the enzyme that makes messenger RNA based on a DNA template. The T7 enzyme has a single subunit, and is more like chloroplast and mitochondrial enzymes than those of bacteria or the cell.

Credit: Thomas Splettstoesser (25 June 2007)

Map showing the distribution of coronavirus cases; black: highest incidence; dark red to pink: decreasing incidence; grey: no recorded cases

2 April: The ongoing pandemic of a novel coronavirus is accelerating rapidly; more than 900,000 confirmed cases, including more than 45,000 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

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

28 February: The World Health Organization raises its assessment of the global risk from the ongoing outbreak of respiratory disease caused by a novel coronavirus to "very high". WHO

False-coloured electron micrograph of novel coronavirus

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

Virus classification is the process of naming viruses and placing them into a taxonomic system. Viruses do not fit neatly into the biological classification system used for cellular organisms. They are mainly classified by phenotypic characteristics, such as morphology, nucleic acid type, mode of replication, host organisms and the type of disease they cause.

Two schemes are in common use. The Baltimore classification (pictured), proposed in 1971 by David Baltimore, places viruses into seven groups (I–VII) based on their nucleic acid type, number of strands and sense, as well as the method the virus uses to generate mRNA. The International Committee on Taxonomy of Viruses, established in the early 1970s, classifies viruses into groupings similar to those used for cellular organisms, which reflect viruses thought to have a common ancestor. As of 2019, one phylum, 6 classes, 14 orders, 143 families, 846 genera and 4,958 species of viruses have been defined. The majority of virus families have not yet been assigned to an order.

In the severe acute respiratory syndrome (SARS) outbreak, the first cases of the newly emerged SARS coronavirus were reported in November 2002 from the Chinese Guangdong province. The virus soon spread across Asia, with China, Hong Kong, Taiwan and Singapore being the worst affected countries; a secondary outbreak occurred in Canada. The rapid initial spread of the outbreak has been in part attributed to China's slow response to the early cases. Over 8,000 people were infected, with a case fatality rate of 11%. Those over 65 years had a much higher mortality rate, greater than 55%. The outbreak was contained by July 2003, and no cases have been reported since 2004.

At the time of the outbreak, the immediate source of SARS coronavirus was thought to have been the masked palm civet (Paguma larvata; pictured), which was sold as food in Guangdong markets. The virus was also found in raccoon dogs, ferret badgers and domestic cats. More recent research has suggested that the natural reservoir could be horseshoe bats.

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