Poliomyelitis, also called polio or infantile paralysis, was one of the most feared childhood diseases of the 20th century. It has caused paralysis and death for much of human history. The causative agent, poliovirus, spreads via the faecal–oral route. Infections are usually asymptomatic, but in about 1% of cases, the virus enters the central nervous system and preferentially infects and destroys motor neurons, leading to muscle weakness and acute flaccid paralysis. Spinal polio is the most common form, accounting for nearly 80% of cases of paralytic polio; it is characterized by asymmetric paralysis usually involving the legs. Bulbar involvement is rare, but in severe cases the virus can affect the phrenic nerve and prevent breathing, so that patients require mechanical ventilation with an iron lung or similar device.
Polio had existed for thousands of years as an endemic pathogen until the 1880s, when major epidemics began to occur in Europe and later the United States. Polio vaccines developed in the 1950s have reduced the annual incidence from many hundreds of thousands to under a thousand, and as of 2013, a global eradication campaign is ongoing.
Plant viruses face different challenges from animal viruses. As plants do not move, transmission between hosts often involves vectors, most commonly insects, but also fungi, 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. Plant viruses often cause disease, and are thought to cause up to US$60 billion losses to global crop yields each year.
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.
24 March: A small study of a multivalent norovirus virus-like particle vaccine shows a broad antibody response is generated, which covers novel virus variants. PLOS Med
24 March: An Ebola vaccine (virus pictured) based on the 2014 strain is shown to be safe and to generate an immune response in a phase I clinical trial in China. Lancet
23 March: A novel virus, ANMV-1, believed to infect anaerobic archaea in a deep-sea methane seep, is shown to have the first diversity-generating retroelement found in archaea or their viruses, which has the potential to generate rapid genetic diversity in the virus. Nat Comm
22 March: The lowest weekly total of new cases of Ebola virus disease in 2015 has been recorded in the ongoing West African outbreak; since the outbreak began, there have been nearly 25,000 suspected cases and 10,326 deaths. WHO
18 March: A test to distinguish viral from bacterial infections is developed, based on TRAIL (pictured) and other host proteins induced after infection. PLOS ONE
10 March: In the ongoing outbreak of Middle East respiratory syndrome coronavirus (MERS-CoV; pictured), cases continue to be reported in Saudi Arabia; since the outbreak started in September 2012, there have been 1075 cases with at least 404 deaths. WHO
9 March: Real-time imaging of SIV in macaques using immuno-PET reveals unexpectedly high levels of virus in the nasal cavity, lung and male genital tract in antiretroviral-treated animals. Nat Meth
4 March: The International Committee on Taxonomy of Viruses formally ratify their 2014 species list, with one new family of double-stranded DNA bacteriophages, Sphaerolipoviridae, one new subfamily of Myoviridae, Eucampyvirinae, fifty new genera and 359 new species recognised. ICTV
3 March: Four RNA viruses found in farmed honeybees – acute bee paralysis, black queen cell, deformed wing and slow bee paralysis viruses – are widespread among wild bumblebee species in a survey across Britain. J Anim Ecol
2 March: A 3D image of Acanthamoeba polyphaga mimivirus at 125 nm resolution is constructed from multiple high-energy X-ray diffraction patterns of single virions, rather than crystals, in the first application of this technique to a virus. Nature
25 February: H7N9 avian influenza infection continues in China, with 59 cases reported since 21 January. WHO
25 February: WHO calls for increased measles vaccination coverage in the light of outbreaks across Europe; the ongoing outbreak in North America continues. WHO,CDC
24 February: A clinical trial in England shows that pre-exposure prophylaxis with tenofovir/emtricitabine (Truvada) reduces the risk of HIV infection by 86% in gay men engaging in high-risk sex. CROI
18 February: Varicella zoster virus antigens are found in 74% of giant cell arteritis biopsies but only 8% of normal ones, suggesting the virus might have a role in triggering disease. Neurology
29 January: A total of 112 novel negative-sense RNA viruses of arthropods, including a putative new family of circular RNA viruses, are identified in a study of 70 arthropod species in China. e-Life