In HIV, the envelope that covers the virion is formed from the outermost membrane of the host cell; such "self-cloaked" viruses make it difficult for the immune system to identify them as "non-self" structures. History of immunology
Immunology is a science that examines the structure and function of the immune system. It originates from medicine and early studies on the causes of immunity to disease. The earliest known reference to immunity was during the plague of Athens in 430 BC. Thucydides noted that people who had recovered from a previous bout of the disease could nurse the sick without contracting the illness a second time. In the 18th century, Pierre-Louis Moreau de Maupertuis experimented with scorpion venom and observed that certain dogs and mice were immune to this venom. In the 10th century, Persian physician al-Razi (also known as Rhazes) wrote the first recorded theory of acquired immunity, noting that a smallpox bout protected its survivors from future infections. Although he explained the immunity in terms of "excess moisture" being expelled from the blood—therefore preventing a second occurrence of the disease—this theory explained many observations about smallpox known during this time.These and other observations of acquired immunity were later exploited by Louis Pasteur in his development of vaccination and his proposed germ theory of disease. Pasteurs theory was in direct opposition to contemporary theories of disease, such as the miasma theory.
Ghost sickness is a cultural belief among some traditional indigenous peoples in North America, notably the Navajo, and some Muscogee and Plains cultures, as well as among Polynesian peoples. People who are preoccupied and/or consumed by the deceased are believed to suffer from ghost sickness. Reported symptoms can include general weakness, loss of appetite, suffocation feelings, recurring nightmares, and a pervasive feeling of terror. The sickness is attributed to ghosts or, occasionally, to witches or witchcraft. Cultural background
In the Muscogee (Creek) culture, it is believed that everyone is a part of an energy called Ibofanga. This energy supposedly results from the flow between mind, body, and spirit. Illness can result from this flow being disrupted. Therefore, their "medicine is used to prevent or treat an obstruction and restore the peaceful flow of energy within a person". Purification rituals for mourning "focus on preventing unnatural or prolonged emotional and physical drain. "The traditional Native American grief resolution process is qualitatively different from those usually seen in mainstream Western cultures. In 1881, there was a federal ban on some of the traditional mourning rituals practised by the Lakota and other tribes. Lakota expert Maria Yellow Horse Brave Heart proposes that the loss of these rituals may have caused the Lakota to be "further predisposed to the development of pathological grief".