Portal:Viruses

Alphaviruses are a genus of RNA viruses in the Togaviridae family. The spherical enveloped virion is 70 nm in diameter, with a nucleocapsid of 40 nm. It has a single-stranded, positive-sense RNA genome of 11–12 kb. The genus contains more than thirty species, which infect humans, horses, rodents and other mammals, as well as fish, birds, other vertebrates and invertebrates. Alphaviruses are generally transmitted by insect vectors, predominantly mosquitoes, and are an example of arboviruses (arthropod-borne viruses).

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. Some members of the genus cause significant disease in humans, including the chikungunya, o'nyong'nyong, Ross River, Sindbis, Barmah Forest and Semliki Forest (pictured) viruses and the eastern, western and Venezuelan equine encephalitis viruses. Arthritis, encephalitis, rashes and fever are the most frequently observed symptoms. Large mammals such as humans usually form dead-end hosts for the viruses, although Venezuelan equine encephalitis virus is mainly amplified in the horse. No human vaccine or antiviral drug has been licensed. Prevention is predominantly by control of the insect vector.

• ...that the recently discovered Zamilon virophage (pictured) casts doubt on the concept of virophages?
• ...that as many as 3.3 million newborns die each year, of which 23.4% succumb to neonatal infection?
• ...that Robert Shope, described as a "walking encyclopaedia" of arboviruses, discovered more novel viruses than anyone previously?
• ...that the common banded mosquito is a vector for Murray Valley encephalitis virus, Ross River virus, and Japanese encephalitis, as well as dog heartworm and the roundworm Wuchereria bancrofti?
• ...that Zeblon Gwala, the inventor of the purported HIV/AIDS treatment ubhejane, has said he got the idea for its ingredients in a dream?

Many well-known people have survived the paralytic disease polio. The earliest identified case might be Siptah (pictured), Egyptian pharaoh 1197–1191 BC, whose mummified remains have a deformed leg possibly from polio. Claudius, Roman emperor 41–54 AD, walked with a limp after a childhood disease that historians have hypothesised might have been polio. Novelist Sir Walter Scott suffered paralysis in one leg after a teething fever in 1773, which left him lame; his detailed account of his disease has allowed a retrospective diagnosis of polio to be made with confidence.

For many of those who survived it, paralytic polio was a life-changing experience. The disease can lead to permanent physical disability; Itzhak Perlman, for example, plays the violin seated. Others recover completely, with some going on to excel in sports; Ray Ewry became world's foremost standing jumper after childhood polio. Some survivors, including singer Ian Dury and actress Mia Farrow, have campaigned for polio eradication or for disability rights.

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

Two polio vaccines are used against the paralytic disease polio. The first, developed by Jonas Salk, consists of inactivated poliovirus. Based on three wild virulent strains, inactivated using formalin, it is administered by injection and is very safe. It confers IgG-mediated immunity, which prevents poliovirus from entering the bloodstream and protects the motor neurons, eliminating the risk of bulbar polio and post-polio syndrome. The second, developed by Albert Sabin, originally consisted of three live virus strains, attenuated by growth in cell culture. Since 2016, only two strains have generally been included. They contain multiple mutations, preventing them from replicating in the nervous system. The Sabin vaccine stimulates both antibodies and cell-mediated immunity, providing longer-lasting immunity than the Salk vaccine. It can be administered orally, making it more suitable for mass vaccination campaigns. In around three cases per million doses, the live vaccine reverts to a virulent form and causes paralysis. Vaccination has reduced the number of wild-type polio cases from around 350,000 in 1988 to just 33 in 2018, and eradicated the disease from most countries.

Subcategories of virology: