Portal:Viruses

Zika fever is caused by the Zika virus, a mosquito-borne flavivirus first isolated in Uganda in 1947. Human infection is usually asymptomatic; a minority of cases have mild symptoms, which generally last 2–7 days and can include fever, conjunctivitis, joint pain, headache and a maculopapular rash. Infections in adults have occasionally been associated with Guillain–Barré syndrome. The incubation period is probably up to a week. The natural reservoir is unknown. The virus is transmitted by Aedes mosquitoes, mainly Aedes aegypti in tropical regions. During pregnancy, mother-to-child transmission can cause microcephaly (pictured) and other brain malformations in some babies. In one study, major abnormalities were seen in 42% of live births. The virus is present in semen and male-to-female sexual transmission has been documented; it is also found in breast milk and blood.

The first documented human outbreak occurred in 2007 in the Federated States of Micronesia. The virus is thought to have entered the Americas in around 2013, and an outbreak started in Brazil in 2015, spreading across the Americas and to Pacific, Asia and Africa, and leading the World Health Organization to consider Zika a Public Health Emergency of International Concern in February–November 2016. No specific treatment nor vaccine has been approved. Prevention involves mosquito control and condom use; women in areas where Zika was circulating were recommended to consider delaying pregnancy, and pregnant women were advised to avoid travel to affected areas.

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)

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

Plant viruses face different challenges from animal viruses. As plants do not move, transmission between hosts often involves vectors, most commonly insects, but also nematodes and protozoa. Plant viruses can also spread via seeds, and by direct transfer of sap. Plant cells are surrounded by cell walls which are difficult to penetrate. Movement between cells occurs mainly by transport through plasmodesmata, and most plant viruses encode movement proteins to make this possible. Although plants lack an adaptive immune system, they have complex defences against viral infection. Viruses of cultivated plants often cause disease, and are thought to cause up to US$60 billion losses to global crop yields each year; infections of wild plants are often asymptomatic.

Most plant viruses are rod-shaped, with protein discs forming a tube surrounding the viral genome; isometric particles are another common structure. They rarely have an envelope. The great majority have an RNA genome, which is usually small and single stranded. Plant viruses are grouped into 73 genera and 49 families. Tobacco mosaic virus (pictured) is among the best characterised of the 977 species officially recognised in 1999.

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.

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