disease

Human diseases disturb or damage the functioning of cells, tissues, organs, or systems. They are usually characterized by specific symptoms and signs, and can be mild and short lasting - such as the common cold - or severe enough to kill millions, such as the influenza pandemic that swept the world in 1918-19. Diseases can be infectious or non-infectious. Infectious diseases are caused by microorganisms, such as bacteria and viruses, invading the body; they can be spread between people by direct or indirect contact. Non-infectious diseases can have many causes: they may be inherited (congenital diseases); they can result from poor nutrition or hygiene; or they may arise from injury or ageing. The causes of some diseases are still unknown.

Some diseases are related to the conditions in which people live. The Romans understood this and avoided building their towns or army camps near to marshes. Although they did not understand about the spread of germs, they recognized that the conditions found in damp marshes led to increased illness and disease. Similarly, the filthy living conditions in 19th-century British cities, such as London and Manchester, led to mass outbreaks of diseases such as cholera and typhoid fever. Dirty drinking water and the lack of proper sanitation spread the bacteria associated with these diseases.

The ancient world The ability of the medical profession to stop the spread of disease and to treat disease once present in a patient has developed over time. Prehistoric people blamed disease on the gods and evil spirits; techniques used in prehistoric medicine included trepanning (cutting a hole in the patient's skull) to try to remove the evil spirit from the affected person. The Egyptians continued to focus on religious explanations of disease, but ancient Egyptian medicine developed new ideas, such as the theory that disease and illness were the result of the body's channels becoming blocked. To treat this the Egyptians used medicines such as purgatives to make the patient vomit and laxatives to empty the patient's bowels. The Hippocratic school of ancient Greek medicine developed this further. Hippocrates developed the theory of the humours (four body fluids: blood, phlegm, yellow bile, and black bile), and explained disease and illness as a result of the imbalance of the body's humours. Both the Egyptians and the Greeks, however, continued to rely on religious explanations for disease. The Egyptians focused on gods such as Sekhmet, who was believed to both cause and cure epidemics. They also wore scarab beetle brooches to ward off the evil spirits that caused illness; the scarab was believed to be a symbol of resurrection. The Greeks believed in the god of healing, Asclepius, and visited his temples (asclepia) to be cured of their illness and disease. In the Roman period, belief in the spiritual cause of disease continued; Roman medicine was heavily influenced by Greek ideas, and the Romans adopted Asclepius, building asclepia as well as praying to their native gods.

As well as holding on to their religious beliefs, the Egyptians, Greeks, and Romans made use of common sense or rational preventative measures to keep themselves healthy. Many of their religious rituals and social practices were also medically beneficial and, although this was an unintended side effect, such customs improved the health of the population. Egyptian priests washed every day and shaved their body hair on a regular basis, and this observance spread among the Egyptian people. The Greeks were encouraged to have a healthy lifestyle or ‘regimen’ by Hippocratic doctors. They followed the ideas in the Hippocratic text A Programme For Health, in which Hippocrates encouraged healthy eating as well as exercise and cleanliness. Although Hippocrates had no knowledge of germs, he had made a connection between illness and lifestyle. Much of the treatment received in an asclepion was related to a healthy lifestyle. The asclepia gave their patients a healthy diet as well as the use of running tracks and baths. Such ideas were continued by the Romans, many of whom adopted the Hippocratic beliefs. In addition the Romans developed an extensive public health system that provided clean water and reasonably effective sanitation to their cities, helping to prevent the spread of disease. Romans visited the public baths for relaxation and to socialize, as well as for their health. Although the Romans did little to advance medical understanding of disease, the Roman Empire's public health measures meant that people living in Rome in AD 30 lived longer and healthier lives than people in London in AD 1500.

The Dark Ages and Middle Ages Following the collapse of the Roman Empire in AD 476 people fell back on religious explanations of disease, abandoning much of the progress of the Egyptians, Greeks, and Romans. With the dominance of the Roman Catholic Church in Europe in this period, and the lack of any attempt by governments to deal with health problems, medical knowledge was unable to advance in the field of disease. When the Black Death, an epidemic of plague, struck Europe in the 14th century, explanations included the movements of the planets, religion, the four humours, and invisible but poisonous fumes or miasmas. Some people explained the Black Death by the dirt and smells coming from the filthy towns, but most relied on religion and astrology. Efforts were made to clean up the towns, with laws banning the depositing of rubbish and animal waste in the streets or rivers, but these were not properly enforced, and doctors had no real understanding of the causes of disease or how to cure it.

The Renaissance Although there were great advances in anatomical knowledge in Renaissance medicine, the understanding of disease did not make the same progress. Religious explanations of disease continued to dominate, and doctors carried on using the methods of Hippocrates and Galen to balance the humours of the body. For instance, when King Charles II of England was dying in 1685 he was treated using methods that included bleeding and purging. Ordinary people used traditional methods such as herbal remedies and foods such as rhubarb.

Modern medicine The explanation, prevention, and cure of disease advanced most rapidly in the period after 1700. The first new method to be used was inoculation for smallpox: the infection of a healthy person with a mild dose of the disease so as to build up a resistance to it. Lady Wortley Montagu introduced inoculation to Britain in 1721, having seen it in use in Turkey. However, although inoculation was effective, it did not actually advance scientific understanding of disease, as doctors were unable to develop a proper explanation for exactly how it worked. The next breakthrough came in 1796 when Edward Jenner developed the first vaccine for a disease. He used the milder disease of cowpox to prevent his patients from getting smallpox, but was unable to explain why it worked.

In 19th-century medicine, knowledge concerning disease advanced rapidly from the 1860s after Louis Pasteur developed his germ theory of disease, showing that disease was the result of germs infecting the patient. Doctors such as Robert Koch, Emil Behring, and Paul Ehrlich took this work further. Koch identified the bacteria that caused many specific diseases including tuberculosis and cholera. In the 1880s doctors, including Pasteur, developed new vaccinations for diseases such as rabies, cholera, and anthrax. In the 1890s Emil Behring developed the first antitoxin that could counteract the poisons produced by a disease in the human body, and developed new treatments for diseases such as diphtheria.

Problems remained, however, particularly as antitoxins often harmed the rest of the body. The advances of 20th-century medical technology overcame this problem with the development of ‘magic bullets’ that could kill the bacteria causing a disease without harming anything else. The first was Salvarsan 606 developed by Paul Ehrlich in 1909 to treat syphilis. In 1935 Gerhard Domagk discovered Prontosil, another ‘magic bullet’, which attacked the streptococcus bacteria that caused blood poisoning. His achievement led to the development of a group of drugs known as the sulphonamides. The most important development in the fight against disease came in 1928 when Alexander Fleming discovered penicillin, the first universal antibiotic. During the 1930s and 1940s Howard Florey and Ernst Chain developed penicillin as a treatment for almost all bacterial infections or diseases. The range of antibacterial agents proliferated in the second half of the 20th century, although their overuse has increased the possibility of resistance as new strains of bacteria emerge.

DNA and genetics Since the investigation of DNA in the 1950s, medical understanding of disease has advanced further than ever. With genetic engineering doctors will be able to change the DNA of human cells before conception to prevent inherited diseases. Science is also developing techniques that will allow the production of treatments for human diseases in the milk and body parts of other animals.