Portal:Viruses

Herpes simplex is caused by herpes simplex virus types 1 and 2 of the Herpesviridae family, with 60–95% of adults being infected with one of the types. Common forms of infection are oral herpes, which can result in cold sores, and genital herpes. Active disease often involves blisters containing infectious virus, although the genital form is frequently asymptomatic. Less common disorders associated with the viruses include herpetic whitlow, herpes gladiatorum, ocular herpes, herpesviral encephalitis and Mollaret's meningitis.

After initial infection, virus particles are transported along sensory nerves to the cell bodies in the ganglion, where they become latent and remain lifelong. Periods of remission alternate with outbreaks of active disease, in which the virus multiplies in the nerve cell and new virus particles are transported along the nerve fibre to the nerve terminals in the skin, where they are released. What causes these recurrences is unclear. Transmission is usually by direct contact with a lesion or with body fluids, and can occur during periods of asymptomatic shedding. Neonatal herpes is possible after transmission from the mother. Barrier protection methods reduce genital herpes risk. No vaccine or cure exists, but antiviral treatment can alleviate symptoms and reduce viral shedding.

Respiratory droplets, such as those expelled during a sneeze, are important in the transmission of several respiratory viruses, including influenza and severe acute respiratory syndrome coronavirus 2. Droplets are also released by breathing, talking, coughing and vomiting, and can be created by aerosol-generating medical procedures.

Credit: James Gathany (2009)

Map showing the prevalence of SARS-CoV-2 cases; black: highest prevalence; dark red to pink: decreasing prevalence; grey: no recorded cases or no data

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

A global drive to eradicate poliovirus started in 1988, when there were an estimated 350,000 cases of wild poliovirus infection globally. Two diseases, both caused by viruses, have been eradicated, smallpox in 1980 and rinderpest in 2011. Poliovirus only infects humans. It persists in the environment for a few weeks at room temperature and a few months at 0–8 °C. The oral polio vaccine is inexpensive, highly effective and is predicted to generate lifelong immunity. Reversion of live vaccine strains to virulence has resulted in occasional cases of vaccine-associated polio paralysis.

Two of the three strains of wild-type poliovirus have been eradicated. Annual reported cases of wild poliovirus infection fell to a low of 22 in 2017, but had risen to 176 in 2019. As of 2020, the wild virus remains endemic only in Afghanistan and Pakistan, but vaccine-derived poliovirus is circulating in several countries. A lack of basic health infrastructure and civil war remain significant obstacles to eradication. Some local communities have opposed immunisation campaigns, and vaccination workers have been murdered in Pakistan and Nigeria.

The 1976 Zaire Ebola virus outbreak was one of the first two recorded outbreaks of the disease. The causative agent was identified as a novel virus, named for the region's Ebola River. The first identified case, in August, worked in the school in Yambuku, a small rural village in Mongala District, north Zaire. He had been treated for suspected malaria at the Yambuku Mission Hospital, which is now thought to have spread the virus by giving vitamin injections with inadequately sterilised needles, particularly to women attending prenatal clinics. Unsafe burial practices also spread the virus.

The outbreak was contained by quarantining local villages, sterilising medical equipment and providing protective clothing to medical personnel, and was over by early November. A total of 318 cases was recorded, of whom 280 died, an 88% case fatality rate. An earlier outbreak in June–November in Nzara, Sudan, was initially thought to be linked, but was shown to have been caused by a different species of Ebola virus.

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