WJEC Biology for A2: Student Bk

Smallpox ▪ Smallpox is caused by a DNA- containing virus, Variola major . ▪ The virus is inhaled or transmitted in saliva or from other bodies if there is close contact with an infected person. ▪ It enters small blood vessels in the skin, mouth and throat and is dispersed around the body. It causes a rash and then fluid-filled blisters, which leave scars in survivors. Some survivors also suffer blindness and limb deformities. ▪ Infected people are given fluids, drugs to control the fever and pain and antibiotics to control bacterial infections, but up to 60% die. ▪ The smallpox vaccine produces a strong immune response. It is made using live Vaccinia virus, a close relative of the smallpox virus, and has been very effective at preventing the disease. Before it was available, infected people were isolated, to prevent the virus spreading. ▪ Throughout history, millions have died from smallpox, including up to 500 million between 1900 and 1979, when it was declared eradicated, following vaccination campaigns that began in the 19th century. It is the only species that humans have deliberately made extinct. The only remaining virus is kept in research labs with very high levels of biosecurity. Ethical debates concerning the final total extinction of the species are ongoing. Influenza ▪ There are three subgroups of the influenza virus, called ’flu A, B and C. ’Flu A is the best known and will be described here. Influenza viruses infect many species; avian (bird) and swine ’flu have provided recurrent sources of new influenza viruses that infect humans. When a new strain of ’flu appears, with new proteins on the virus surface, the human immune system is not able to provide adequate protection. As a result of this lack of immunity, pandemics occur, e.g. in 1918–1920, Spanish ’flu infected 500 million people and killed over 50 million, about 4% of the world’s population, in one of the deadliest natural disasters in human history. ▪ The influenza virus contains RNA as its genetic material, but it is unusual for a virus in that its RNA is in 8 single strands, rather than one. The virion is surrounded by a phospholipid envelope, derived from the host’s cell surface membrane. The envelope contains two important proteins which are antigens and are the spikes on the surface of the virus particle: – Haemagglutinin (H) has a role in the virus entering a host cell. – Neuraminidase (N) has a role in the virus leaving the host cell. Section through Variola major Going further The earliest evidence of smallpox is on the mummy of Pharaoh Ramses V, who died in 1145 BCE, but DNA analysis suggests it emerged as a new disease in humans about 12 000 years ago. Influenza viruses Key Terms Pandemic : An epidemic over a very wide area, crossing international boundaries, affecting a very large number of people. Antigen : A molecule that causes the immune system to produce antibodies against it. Antigens include individual molecules and those on viruses, bacteria, spores or pollen grains. They may be formed inside the body, e.g. bacterial toxins. St u dy point Gastric 'flu is not caused by an influenza virus. It is caused by bacteria or viruses, such as norovirus, infecting the digestive system. Option A: Immunology and disease 263