Infectious disease
Worldwide mortality due to infectious diseases
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- Percentage of all deaths Deaths 1993 (in millions) 1993 Rank
- Historic pandemics
- Emerging diseases
The top three single agent/disease killers are HIV/AIDS, TB and malaria. While the number of deaths due to nearly every disease have decreased, deaths due to HIV/AIDS have increased fourfold. Childhood diseases include pertussis, poliomyelitis, diphtheria, measles and tetanus. Children also make up a large percentage of lower respiratory and diarrheal deaths. In 2012, approximately 3.1 million people have died due to lower respiratory infections, making it the number 4 leading cause of death in the world.[82] Historic pandemics[edit] See also: List of epidemics Great Plague of Marseille in 1720 killed 100,000 people in the city and the surrounding provinces With their potential for unpredictable and explosive impacts, infectious diseases have been major actors in human history.[83] A pandemic (or global epidemic) is a disease that affects people over an extensive geographical area. For example: Plague of Justinian, from 541 to 542, killed between 50% and 60% of Europe's population.[84] The Black Death of 1347 to 1352 killed 25 million in Europe over 5 years. The plague reduced the old world population from an estimated 450 million to between 350 and 375 million in the 14th century. The introduction of smallpox, measles, and typhus to the areas of Central and South America by European explorers during the 15th and 16th centuries caused pandemics among the native inhabitants. Between 1518 and 1568 disease pandemics are said to have caused the population of Mexico to fall from 20 million to 3 million.[85] The first European influenza epidemic occurred between 1556 and 1560, with an estimated mortality rate of 20%.[85] Smallpox killed an estimated 60 million Europeans during the 18th century[86] (approximately 400,000 per year).[87] Up to 30% of those infected, including 80% of the children under 5 years of age, died from the disease, and one-third of the survivors went blind.[88] In the 19th century, tuberculosis killed an estimated one-quarter of the adult population of Europe;[89] by 1918 one in six deaths in France were still caused by TB. The Influenza Pandemic of 1918 (or the Spanish flu) killed 25–50 million people (about 2% of world population of 1.7 billion).[90] Today Influenza kills about 250,000 to 500,000 worldwide each year. Emerging diseases[edit] In most cases, microorganisms live in harmony with their hosts via mutual or commensal interactions. Diseases can emerge when existing parasites become pathogenic or when new pathogenic parasites enter a new host. Coevolution between parasite and host can lead to hosts becoming resistant to the parasites or the parasites may evolve greater virulence, leading to immunopathological disease. Human activity is involved with many emerging infectious diseases, such as environmental change enabling a parasite to occupy new niches. When that happens, a pathogen that had been confined to a remote habitat has a wider distribution and possibly a new host organism. Parasites jumping from nonhuman to human hosts are known as zoonoses. Under disease invasion, when a parasite invades a new host species, it may become pathogenic in the new host.[91] Several human activities have led to the emergence of zoonotic human pathogens, including viruses, bacteria, protozoa, and rickettsia,[92] and spread of vector-borne diseases,[91] see also globalization and disease and wildlife disease: Encroachment on wildlife habitats. The construction of new villages and housing developments in rural areas force animals to live in dense populations, creating opportunities for microbes to mutate and emerge.[93] Changes in agriculture. The introduction of new crops attracts new crop pests and the microbes they carry to farming communities, exposing people to unfamiliar diseases. The destruction of rain forests. As countries make use of their rain forests, by building roads through forests and clearing areas for settlement or commercial ventures, people encounter insects and other animals harboring previously unknown microorganisms. Uncontrolled urbanization. The rapid growth of cities in many developing countries tends to concentrate large numbers of people into crowded areas with poor sanitation. These conditions foster transmission of contagious diseases. Modern transport. Ships and other cargo carriers often harbor unintended "passengers", that can spread diseases to faraway destinations. While with international jet-airplane travel, people infected with a disease can carry it to distant lands, or home to their families, before their first symptoms appear. Germ theory of disease[edit] Main article: Germ theory of disease East German postage stamps depicting four antique microscopes. Advancements in microscopy were essential to the early study of infectious diseases. In Antiquity, the Greek historian Thucydides (c. 460 – c. 400 BCE) was the first person to write, in his account of the plague of Athens, that diseases could spread from an infected person to others.[94][95] In his On the Different Types of Fever (c. 175 AD), the Greco-Roman physician Galen speculated that plagues were spread by "certain seeds of plague", which were present in the air.[96] In the Sushruta Samhita, the ancient Indian physician Sushruta theorized: "Leprosy, fever, consumption, diseases of the eye, and other infectious diseases spread from one person to another by sexual union, physical contact, eating together, sleeping together, sitting together, and the use of same clothes, garlands and pastes."[97][98] This book has been dated to about the sixth century BC.[99] A basic form of contagion theory was proposed by Persian physician Ibn Sina (known as Avicenna in Europe) in The Canon of Medicine (1025), which later became the most authoritative medical textbook in Europe up until the 16th century. In Book IV of the Canon, Ibn Sina discussed epidemics, outlining the classical miasma theory and attempting to blend it with his own early contagion theory. He mentioned that people can transmit disease to others by breath, noted contagion with tuberculosis, and discussed the transmission of disease through water and dirt.[100] The concept of invisible contagion was later discussed by several Islamic scholars in the Ayyubid Sultanate who referred to them as najasat ("impure substances"). The fiqh scholar Ibn al-Haj al-Abdari (c. 1250–1336), while discussing Islamic diet and hygiene, gave warnings about how contagion can contaminate water, food, and garments, and could spread through the water supply, and may have implied contagion to be unseen particles.[101] When the Black Death bubonic plague reached Al-Andalus in the 14th century, the Arab physicians Ibn Khatima (c. 1369) and Ibn al-Khatib (1313–1374) hypothesised that infectious diseases were caused by "minute bodies" and described how they can be transmitted through garments, vessels and earrings.[102] Ideas of contagion became more popular in Europe during the Renaissance, particularly through the writing of the Italian physician Girolamo Fracastoro.[103] Anton van Leeuwenhoek (1632–1723) advanced the science of microscopy by being the first to observe microorganisms, allowing for easy visualization of bacteria. In the mid-19th century John Snow and William Budd did important work demonstrating the contagiousness of typhoid and cholera through contaminated water. Both are credited with decreasing epidemics of cholera in their towns by implementing measures to prevent contamination of water.[104] Louis Pasteur proved beyond doubt that certain diseases are caused by infectious agents, and developed a vaccine for rabies. Robert Koch provided the study of infectious diseases with a scientific basis known as Koch's postulates. Edward Jenner, Jonas Salk and Albert Sabin developed effective vaccines for smallpox and polio, which would later result in the eradication and near-eradication of these diseases, respectively. Alexander Fleming discovered the world's first antibiotic, penicillin, which Florey and Chain then developed. Gerhard Domagk developed sulphonamides, the first broad spectrum synthetic antibacterial drugs. Yüklə 443,06 Kb. Dostları ilə paylaş:
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