An infectious disease is a clinically evident disease resulting from the presence of pathogenic microbial agents, including pathogenic viruses, pathogenic bacteria, fungi, protozoa, multicellular parasites, and aberrant proteins known as prions. A disease is an abnormal condition of an organism that impairs bodily functions and can be deadly Pathogenic microbes are Microbes that cause Infectious diseases This article is dedicated to human pathogenic microbes Pathogenic bacteria are Bacteria that cause Infectious diseases. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular Parasitism is a type of symbiotic relationship between Organisms of different Species. A prion (ˈpriːɒn is thought to be an infectious agent that according to current scientific consensus is comprised entirely of a propagated, mis-folded These pathogens are able to cause disease in animals and/or plants. A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious
Infectious pathologies are usually qualified as contagious diseases (also called communicable diseases) due to their potentiality of transmission from one person or species to another.  Transmission of an infectious disease may occur through one or more of diverse pathways including physical contact with infected individuals. These infecting agents may also be transmitted through liquids, food, body fluids, contaminated objects, airborne inhalation, or through vector-borne spread. In Epidemiology, a vector is an Organism that does not cause Disease itself but which transmits Infection by conveying Pathogens from 
The term infectivity describes the ability of an organism to enter, survive and multiply in the host, while the infectiousness of a disease indicates the comparative ease with which the disease is transmitted to other hosts. In Epidemiology, infectivity refers to the ability of a Pathogen to establish an infection  An infection however, is not synonymous with an infectious disease, as an infection may not cause important clinical symptoms or impair host function. An infection is the detrimental Colonization of a host Organism by a foreign Species. This article deals with the general meaning of the term "synonym" 
Among the almost infinite varieties of microorganisms, relatively few cause disease in otherwise healthy individuals.  Infectious disease results from the interplay between those few pathogens and the defenses of the hosts they infect. The appearance and severity of disease resulting from any pathogen depends upon the ability of that pathogen to damage the host as well as the ability of the host to resist the pathogen. Infectious microorganisms, or microbes, are therefore classified as either primary pathogens or as opportunistic pathogens according to the status of host defenses.
Primary pathogens cause disease as a result of their presence or activity within the normal, healthy host, and their intrinsic virulence (the severity of the disease they cause) is, in part, a necessary consequence of their need to reproduce and spread. Virulence (also called pestiferousness) refers to the degree of Pathogenicity of a Microbe, or in other words the relative ability of a Microbe Many of the most common primary pathogens of humans only infect humans, however many serious diseases are caused by organisms acquired from the environment or which infect non-human hosts.
Organisms which cause an infectious disease in a host with depressed resistance are classified as opportunistic pathogens. Opportunistic disease may be caused by microbes that are ordinarily in contact with the host, such as pathogenic bacteria or fungi in the gastrointestinal or the upper respiratory tract, and they may also result from (otherwise innocuous) microbes acquired from other hosts (as in Clostridium difficile colitis) or from the environment as a result of traumatic introduction (as in surgical wound infections or compound fractures). Pathogenic bacteria are Bacteria that cause Infectious diseases. The Upper respiratory tract refers to the following parts of the Respiratory system: Nose and Oral cavity Throat Clostridium difficile (pronounced /klɒsˈtrɪdiəm dɪˈfɪsɪli/ also known as CDF/cdf' or 'C Colitis is a chronic digestive disease characterized by Inflammation of the colon. Treatment of physical trauma is described here and in First aid. Surgery (from the χειρουργική cheirourgikē, via chirurgiae meaning "hand work" is a medical specialty that uses operative manual and instrumental A bone fracture (sometimes abbreviated # or Fx or Fx) is a medical condition in which a Bone is cracked or broken An opportunistic disease requires impairment of host defenses, which may occur as a result of genetic defects (such as Chronic granulomatous disease), exposure to antimicrobial drugs or immunosuppressive chemicals (as might occur following poisoning or cancer chemotherapy), exposure to ionizing radiation, or as a result of an infectious disease with immunosuppressive activity (such as with measles, malaria or HIV disease). A genetic disorder is a condition caused by abnormalities in Genes or Chromosomes While some diseases such as Cancer, are due to genetic abnormalities acquired Chronic granulomatous disease (CGD is a diverse group of hereditary diseases in which certain cells of the Immune system have difficulty forming the reactive An antimicrobial is a substance that kills or inhibits the growth of Microbes such as Bacteria, Fungi, or Viruses. Immunosuppression involves an act that reduces the activation or Efficacy of the Immune system. In the context of Biology, poisons are substances that can cause damage, Illness, or Death to Organisms usually by Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled Chemotherapy, in its most general sense refers to treatment of disease by chemicals that kill cells specifically those of micro-organisms or Cancer. Image talkNew_radiation_symbol_ISO_21482svg for details --> Ionizing radiation Measles (rubeola is a Disease caused by a virus specifically a Paramyxovirus of the genus Morbillivirus. Malaria is a vector -borne Infectious disease caused by Protozoan Parasites It is widespread in tropical and subtropical regions including Human immunodeficiency virus ( HIV) is a Lentivirus (a member of the Retrovirus family that can lead to acquired immunodeficiency syndrome Primary pathogens may also cause more severe disease in a host with depressed resistance than would normally occur in an immunosufficient host.
One way of proving that a given disease is "infectious", is to satisfy Koch's postulates (first proposed by Robert Koch), which demands that the infectious agent be identified only in patients and not in healthy controls, and that patients who contract the agent also develop the disease. Koch's postulates are four criteria designed to establish a causal relationship between a causative Microbe and a Disease. Heinrich Hermann Robert Koch ( December 11 1843 – May 27 1910) was a German Physician. A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious These postulates were first used in the discovery that Mycobacteria species cause tuberculosis. Mycobacterium is a Genus of Actinobacteria, given its own family the Mycobacteriaceae Tuberculosis (abbreviated as TB for tubercle bacillus or T u' b' erculosis Bacillus --> is a common Koch's postulates cannot be met ethically for many human diseases because they require experimental infection of a healthy individual with a pathogen produced as a pure culture. Often, even diseases that are quite clearly infectious do not meet the infectious criteria. For example, Treponema pallidum, the causative spirochete of syphilis, cannot be cultured in vitro - however the organism can be cultured in rabbit testes. Treponema pallidum is a Gram-negative Spirochaete Bacterium. There are at least four known Subspecies: T Spirochaetes is a phylum of distinctive Gram-negative bacteria, which have long helically coiled cells Syphilis is a Sexually transmitted disease caused by the spirochetal Bacterium Treponema pallidum pallidum. A microbiological culture, AKA microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory The testicle (from Latin testiculus, diminutive of testis, meaning "witness" virility plural testes) is the male It is less clear that a pure culture comes from an animal source serving as host than it is when derived from microbes derived from plate culture. Epidemiology is another important tool used to study disease in a population. Epidemiology is the study of factors affecting the Health and Illness of populations and serves as the foundation and Logic of interventions made in the For infectious diseases it helps to determine if a disease outbreak is sporadic (occasional occurrence), endemic (regular cases often occurring in a region), epidemic (an unusually high number of cases in a region), or pandemic (a global epidemic). Outbreak is a classification used in Epidemiology to describe a small localized group of people or organisms infected with a disease In Epidemiology, an Infection is said to be endemic (from Greek en- in or within + demos people in a Population when In Epidemiology, an epidemic (from Greek epi- upon + demos people is a classification of a disease that appears as new cases in a A pandemic (from Greek παν pan all + δήμος demos people is an Epidemic of Infectious disease that spreads through
An infectious disease is transmitted from some source. Defining the means of transmission plays an important part in understanding the biology of an infectious agent, and in addressing the disease it causes. Transmission may occur through several different mechanisms. Respiratory diseases and meningitis are commonly acquired by contact with aerosolized droplets, spread by sneezing, coughing, talking, kissing or even singing. In Animal physiology, respiration is the transport of Oxygen from the outside air to the cells within tissues and the transport of Carbon dioxide Meningitis is Inflammation of the protective membranes covering the Brain and Spinal cord, known collectively as the Meninges. Gastrointestinal diseases are often acquired by ingesting contaminated food and water. Sexually transmitted diseases are acquired through contact with bodily fluids, generally as a result of sexual activity. A sexually transmitted disease ( STD) or venereal disease ( VD) is an illness that has a significant probability of transmission between Humans Some infectious agents may be spread as a result of contact with a contaminated, inanimate object (known as a fomite), such as a coin passed from one person to another, while other diseases penetrate the skin directly. A fomite is any inanimate object or Substance capable of carrying Infectious organisms (such as Germs or Parasites and hence transferring The skin is the outer covering of living tissue of an animal (or plant 
Transmission of infectious diseases may also involve a "vector". In Epidemiology, a vector is an Organism that does not cause Disease itself but which transmits Infection by conveying Pathogens from Vectors may be mechanical or biological. A mechanical vector picks up an infectious agent on the outside of its body and transmits it in a passive manner. An example of a mechanical vector is a housefly, which lands on cow dung, contaminating its appendages with bacteria from the feces, and then lands on food prior to consumption. The housefly (also house fly, house-fly or common housefly) Musca domestica, is the most common of all Flies The pathogen never enters the body of the fly.
In contrast, biological vectors harbor pathogens within their bodies and deliver pathogens to new hosts in an active manner, usually a bite. Biological vectors are often responsible for serious blood-borne diseases, such as malaria, viral encephalitis, Chagas disease, Lyme disease and African sleeping sickness. A blood-borne disease is one that can be spread by contamination by Blood. Malaria is a vector -borne Infectious disease caused by Protozoan Parasites It is widespread in tropical and subtropical regions including Encephalitis is an acute Inflammation of the Brain, commonly caused by a viral Infection. Chagas disease (doença de Chagas enfermedad de Chagas mal de Chagas in both languages also called American trypanosomiasis) is a tropical Parasitic Lyme disease, or borreliosis, is an Emerging infectious disease caused by at least three Species of Bacteria belonging to the Genus Sleeping sickness or human African trypanosomiasis is a Parasitic Disease of people and animals caused by Protozoa of species Biological vectors are usually, though not exclusively, arthropods, such as mosquitoes, ticks, fleas and lice. Arthropods are Animals belonging to the Phylum Arthropoda (from Greek ἄρθρον arthron, " Joint " Mosquitoes are insects in the family Culicidae. They have a pair of scaled wings a pair of Halteres, a slender body and long legs Tick is the common name for the small Arachnids in Superfamily Ixodoidea that along with other Mites constitute the Acarina. Flea is the Common name for any of the small wingless Insects of the order Siphonaptera (some authorities use the name Aphaniptera Lice (singular louse) ( order Phthiraptera) are an order of over 3000 Species of wingless Insects three of which are classified Vectors are often required in the life cycle of a pathogen. A common strategy, used to control vector borne infectious diseases, is to interrupt the life cycle of a pathogen, by killing the vector.
The relationship between virulence and transmission is complex, and has important consequences for the long term evolution of a pathogen. Since it takes many generations for a microbe and a new host species to co-evolve, an emerging pathogen may hit its earliest victims especially hard. It is usually in the first wave of a new disease that death rates are highest. If a disease is rapidly fatal, the host may die before the microbe can get passed along to another host. However, this cost may be overwhelmed by the short term benefit of higher infectiousness if transmission is linked to virulence, as it is for instance in the case of cholera (the explosive diarrhea aids the bacterium in finding new hosts) or many respiratory infections (sneezing and coughing create infectious aerosols). Technically an aerosol is a suspension of fine solid particles or liquid droplets in a gas
One of the ways to prevent or slow down the transmission of infectious diseases is to recognize the different characteristics of various diseases.  Some critical disease characteristics that should be evaluated include virulence, distance traveled by victims, and level of contagiousness. Virulence (also called pestiferousness) refers to the degree of Pathogenicity of a Microbe, or in other words the relative ability of a Microbe The human strains of Ebola virus, for example, incapacitate its victims extremely quickly and kills them soon after. Ebola is the common term for a group of Viruses belonging to genus Ebolavirus, family Filoviridae, and for the disease which they As a result, the victims of this disease do not have the opportunity to travel very far from the initial infection zone.  Also, this virus must spread through skin lesions or permeable membranes such as the eye. Thus, the initial stage of Ebola is not very contagious since its victims experience only internal hemorrhaging. Ebola is the common term for a group of Viruses belonging to genus Ebolavirus, family Filoviridae, and for the disease which they As a result of the above features, the spread of Ebola is very rapid and usually stays within a relatively confined geographical area. Ebola is the common term for a group of Viruses belonging to genus Ebolavirus, family Filoviridae, and for the disease which they In contrast, Human Immunodeficiency Virus (HIV) kills its victims very slowly by attacking their immune system. Human immunodeficiency virus ( HIV) is a Lentivirus (a member of the Retrovirus family that can lead to acquired immunodeficiency syndrome Human immunodeficiency virus ( HIV) is a Lentivirus (a member of the Retrovirus family that can lead to acquired immunodeficiency syndrome  As a result, a lot of its victims transmit the virus to many others before even realizing that they are carrying the disease. Also, the relatively low virulence allows its victims to travel long distances, increasing the likelihood of an epidemic. In Epidemiology, an epidemic (from Greek epi- upon + demos people is a classification of a disease that appears as new cases in a
Another effective way to decrease the transmission rate of infectious diseases is to recognize the effects of small-world networks. In Mathematics and Physics, a small-world network is a type of mathematical graph in which most nodes are not neighbors of one another but most nodes can  In epidemics, there are often extensive interactions within hubs or groups of infected individuals and other interactions within discrete hubs of susceptible individuals. In Epidemiology, an epidemic (from Greek epi- upon + demos people is a classification of a disease that appears as new cases in a Despite the low interaction between discrete hubs, the disease can jump to and spread in a susceptible hub via a single or few interactions with an infected hub. Thus, infection rates in small-world networks can be reduced somewhat if interactions between individuals within infected hubs are eliminated (Figure 1). In Mathematics and Physics, a small-world network is a type of mathematical graph in which most nodes are not neighbors of one another but most nodes can However, infection rates can be drastically reduced if the main focus is on the prevention of transmission jumps between hubs. The use of needle exchange programs in areas with a high density of drug users with HIV is an example of the successful implementation of this treatment method. Human immunodeficiency virus ( HIV) is a Lentivirus (a member of the Retrovirus family that can lead to acquired immunodeficiency syndrome  Another example is the use of ring culling or vaccination of potentially susceptible livestock in adjacent farms to prevent the spread of the foot-and-mouth virus in 2001. Foot-and-mouth disease ( FMD) or hoof-and-mouth disease ( Aphtae epizooticae) is a highly contagious and sometimes fatal viral 
Figure 1: A simplified model of how disease transmission in small-world networks can be prevented. In Mathematics and Physics, a small-world network is a type of mathematical graph in which most nodes are not neighbors of one another but most nodes can Major focus should be on preventing jumps between hubs (green cross out) in addition to prevention within infected hubs (red cross outs).
Diagnosis of infectious disease sometimes involves identifying an infectious agent either directly or indirectly. In practice most minor infectious diseases such as warts, cutaneous abscesses, respiratory system infections and diarrheal diseases are diagnosed by their clinical presentation. A wart (also known as verruca) is generally a small rough Tumor, typically on hands and feet but often other locations that can resemble a Cauliflower The skin is the outer covering of living tissue of an animal (or plant An abscess (abscessus is a collection of Pus (dead Neutrophils) that has accumulated in a cavity formed by the tissue on the basis of an infectious process In living organisms a respiratory system functions to allow Gas exchange. In Medicine, diarrhea, also spelled diarrhoea (see spelling differences) is frequent loose or liquid Bowel movements Acute diarrhea Conclusions about the cause of the disease are based upon the likelihood that a patient came in contact with a particular agent, the presence of a microbe in a community, and other epidemiological considerations. Given sufficient effort, all known infectious agents can be specifically identified. The benefits of identification, however, are often greatly outweighed by the cost, as often there is no specific treatment, the cause is obvious, or the outcome of an infection is benign.
Specific identification of an infectious agent is usually only determined when such identification can aid in the treatment or prevention of the disease, or to advance knowledge of the course of an illness prior to the development of effective therapeutic or preventative measures. For example, in the early 1980s, prior to the appearance of AZT for the treatment of AIDS, the course of the disease was closely followed by monitoring the composition of patient blood samples, even though the outcome would not offer the patient any further treatment options. Zidovudine ( INN) or azidothymidine ( AZT) (also called ZDV is a nucleoside analog reverse transcriptase inhibitor (NRTI a type of Antiretroviral In part, these studies on the appearance of HIV in specific communities permitted the advancement of hypotheses as to the route of transmission of the virus. Human immunodeficiency virus ( HIV) is a Lentivirus (a member of the Retrovirus family that can lead to acquired immunodeficiency syndrome A hypothesis (from Greek) consists either of a suggested explanation for a phenomenon (an event that is observable or of a reasoned proposal suggesting a possible By understanding how the disease was transmitted, resources could be targeted to the communities at greatest risk in campaigns aimed at reducing the number of new infections. The specific serological diagnostic identification, and later genotypic or molecular identification, of HIV also enabled the development of hypotheses as to the temporal and geographical origins of the virus, as well as a myriad of other hypothesis. Serology is the scientific study of blood serum. In practice the term usually refers to the Diagnostic identification of antibodies in the serum The genotype is the genetic constitution of a cell an organism or an individual (i For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of Geography (from Greek γεωγραφία - geografia) is the study of the Earth and its lands features inhabitants and phenomena The development of molecular diagnostic tools have enabled physicians and researchers to monitor the efficacy of treatment with anti-retroviral drugs. Molecular diagnostics are now commonly used to identify HIV in healthy people long before the onset of illness and have been used to demonstrate the existence of people who are genetically resistant to HIV infection. Thus, while there still is no cure for AIDS, there is great therapeutic and predictive benefit to identifying the virus and monitoring the virus levels within the blood of infected individuals, both for the patient and for the community at large.
Diagnosis of infectious disease is nearly always initiated by medical history and physical examination. More detailed identification techniques involve the culture of infectious agents isolated from a patient. Culture allows identification of infectious organisms by examining their microscopic features, by detecting the presence of substances produced by pathogens, and by directly identifying an organism by its genotype. Other techniques (such as X-rays, CAT scans, PET scans or NMR) are used to produce images of internal abnormalities resulting from the growth of an infectious agent. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Computed tomography (CT is a Medical imaging method employing Tomography. Positron emission tomography ( PET) is a Nuclear medicine imaging technique which produces a three-dimensional image or map of functional processes in the The images are useful in detection of, for example, a bone abscess or a spongiform encephalopathy produced by a prion. An abscess (abscessus is a collection of Pus (dead Neutrophils) that has accumulated in a cavity formed by the tissue on the basis of an infectious process Encephalopathy /ɛnˌsɛfəˈlɒpəθi/ literally means Disease of the Brain. A prion (ˈpriːɒn is thought to be an infectious agent that according to current scientific consensus is comprised entirely of a propagated, mis-folded
Microbiological culture is a principal tool used to diagnose infectious disease. A microbiological culture, AKA microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory In a microbial culture, a growth medium is provided for a specific agent. A growth medium or culture medium is a liquid or gel designed to support the growth of Microorganisms or cells There are different types of media for A sample taken from potentially diseased tissue or fluid is then tested for the presence of an infectious agent able to grow within that medium. Most pathogenic bacteria are easily grown on nutrient agar, a form of solid medium that supplies carbohydrates and proteins necessary for growth of a bacterium, along with copious amounts of water. Agar or agar agar is a Gelatinous substance derived from Seaweed. A single bacterium will grow into a visible mound on the surface of the plate called a colony, which may be separated from other colonies or melded together into a "lawn". In Biology, a colony (from Latin colonia) refers to several individual Organisms of the same Species living closely together usually The size, color, shape and form of a colony is characteristic of the bacterial species, its specific genetic makeup (its strain), and the environment which supports its growth. Other ingredients are often added to the plate to aid in identification. Plates may contain substances that permit the growth of some bacteria and not others, or that change color in response to certain bacteria and not others. Bacteriological plates such as these are commonly used in the clinical identification of infectious bacteria. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Microbial culture may also be used in the identification of viruses: the medium in this case being cells grown in culture that the virus can infect, and then alter or kill. A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable In the case of viral identification, a region of dead cells results from viral growth, and is called a "plaque". Eukaryotic parasites may also be grown in culture as a means of identifying a particular agent. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Parasitism is a type of symbiotic relationship between Organisms of different Species.
In the absence of suitable plate culture techniques, some microbes require culture within live animals. Bacteria such as Mycobacterium leprae and T. pallidum can be grown in animals, although serological and microscopic techniques make the use of live animals unnecessary. Viruses are also usually identified using alternatives to growth in culture or animals. Some viruses may be grown in embryonated eggs. An embryo (from Greek:, plural, lit "that which grows" from en- "in" + bryein "to swell be full" is a multicellular Another useful identification method is Xenodiagnosis, or the use of a vector to support the growth of an infectious agent. Chaga's disease is the most significant example, because it is difficult to directly demonstrate the presence of the causative agent, Trypanosoma cruzi in a patient, which therefore makes it difficult to definitively make a diagnosis. Chagas disease (doença de Chagas enfermedad de Chagas mal de Chagas in both languages also called American trypanosomiasis) is a tropical Parasitic Trypanosoma cruzi is a species of parasitic Euglenoid Trypanosomes The species causes the Trypanosomiasis diseases In this case, xenodiagnosis involves the use of the vector of the Chaga's agent T. In Epidemiology, a vector is an Organism that does not cause Disease itself but which transmits Infection by conveying Pathogens from cruzi, an uninfected triatomine bug (subfamily Triatominae), which takes a blood meal from a person suspected of having been infected. The members of Triatominae (trī·ə′täm·ə′nē a subfamily of Reduviidae, are also known as conenose bugs, kissing bugs, assassin bugs The bug is later inspected for growth of T. cruzi within its gut.
Another principle tool in the diagnosis of infectious disease is microscopy. Microscopy is the technical field of using microscopes to view samples or objects Virtually all of the culture techniques discussed above rely, at some point, on microscopic examination for definitive identification of the infectious agent. Microscopy may be carried out with simple instruments, such as the compound light microscope, or with instruments as complex as an electron microscope. Microscopy is the technical field of using microscopes to view samples or objects The optical microscope, often referred to as the "light microscope" is a type of Microscope which uses Visible light and a system of lenses to An electron microscope is a type of Microscope that uses Electrons to illuminate a specimen and create an enlarged image Samples obtained from patients may be viewed directly under the light microscope, and can often rapidly lead to identification. Microscopy is often also used in conjunction with biochemical staining techniques, and can be made exquisitely specific when used in combination with antibody based techniques. Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as Staining is an auxiliary Technique used in Microscopy to enhance contrast in the microscopic image Antibodies (also known as immunoglobulins, abbreviated Ig) are Gamma globulin Proteins that are found in Blood or other Bodily For example, the use of antibodies made artificially fluorescent (fluorescently labeled antibodies) can be directed to bind to and identify a specific antigens present on a pathogen. Antibodies (also known as immunoglobulins, abbreviated Ig) are Gamma globulin Proteins that are found in Blood or other Bodily Fluorescence is a Luminescence that is mostly found as an An antigen (from antibody-generating) or immunogen is a substance that prompts the generation of Antibodies and can cause an immune response A fluorescence microscope is then used to detect fluorescently labeled antibodies bound to internalized antigens within clinical samples or cultured cells. A fluorescence microscope (colloquially synonymous with epifluorescent microscope) is a light Microscope used to study properties of organic or inorganic substances This technique is especially useful in the diagnosis of viral diseases, where the light microscope is incapable of identifying a virus directly.
Other microscopic procedures may also aid in identifying infectious agents. Almost all cells readily stain with a number of basic dyes due to the electrostatic attraction between negatively charged cellular molecules and the positive charge on the dye. A dye can generally be described as a Colored substance that has an affinity to the substrate to which it is being applied Electrostatics is the branch of Science that deals with the Phenomena arising from what seems to be stationary Electric charges Since Classical A cell is normally transparent under a microscope, and using a stain increases the contrast of a cell with its background. Staining a cell with a dye such as Giemsa stain or crystal violet allows a microscopist to describe its size, shape, internal and external components and its associations with other cells. Giemsa stain, named after Gustav Giemsa, an early malariologist is used for the histopathological diagnosis of Malaria and other Parasites It is a mixture Methyl violet is the name given to a group of similar Chemicals used as PH indicators and Dyes Methyl violets are mixtures of tetramethyl pentamethyl and The response of bacteria to different staining procedures is used in the taxonomic classification of microbes as well. Taxonomy is the practice and science of classification The word comes from the Greek, taxis (meaning 'order' 'arrangement' and, nomos Two methods, the Gram stain and the acid-fast stain, are the standard approaches used to classify bacteria and to diagnosis of disease. Gram staining (or Gram's method) is an empirical method of differentiating bacterial species into two large groups ( Gram-positive and Acid-fastness is a physical property of some bacteria referring to their resistance to decolorization by acids during staining procedures The Gram stain identifies the bacterial groups Firmicutes and Actinobacteria, both of which contain many significant human pathogens. The Firmicutes ( Latin: firmus, strong and cutis, skin referring to the cell wall are a division of bacteria, most of which have Gram-positive Actinobacteria or actinomycetes are a group of Gram-positive bacteria with high G+C ratio. The acid-fast staining procedure identifies the Actinobacterial genera Mycobacterium and Nocardia. Mycobacterium is a Genus of Actinobacteria, given its own family the Mycobacteriaceae Nocardia is a Genus of Gram-positive, catalase-positive, rod-shaped Bacteria.
Biochemical tests used in the identification of infectious agents include the detection of metabolic or enzymatic products characteristic of a particular infectious agent. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Since bacteria ferment carbohydrates in patterns characteristic of their genus and species, the detection of fermentation products is commonly used in bacterial identification. Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. Fermentation is the process of deriving energy from the oxidation of organic compounds such as carbohydrates using an endogenous electron acceptor which is Acids, alcohols and gases are usually detected in these tests when bacteria are grown in selective liquid or solid media. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are In Chemistry, an alcohol is any Organic compound in which a Hydroxyl group ( - O[[hydrogen H]]) is bound to a Carbon This page is about the physical properties of gas as a state of matter A growth medium or culture medium is a liquid or gel designed to support the growth of Microorganisms or cells There are different types of media for
The isolation of enzymes from infected tissue can also provide the basis of a biochemical diagnosis of an infectious disease. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins For example, humans can make neither RNA replicases nor reverse transcriptase, and the presence of these enzymes are characteristic of specific types of viral infections. RNA-dependent RNA polymerase ( RDRP) or RNA replicase, is an Enzyme that catalyzes the replication of RNA from an RNA template In Biochemistry, a reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase Enzyme that transcribes The ability of the viral protein hemagglutinin to bind red blood cells together into a detectable matrix may also be characterized as a biochemical test for viral infection, although strictly speaking hemagglutinin is not an enzyme and has no metabolic function. Hemagglutinin (HA or haemagglutinin ( British English) is an Antigenic Glycoprotein found on the surface of the Influenza Viruses Red blood cells are the most common type of Blood cell and the Vertebrate body's principal means of delivering Oxygen to the body tissues via the Blood
Serological methods are highly sensitive, specific and often extremely rapid tests used to identify microorganisms. Serology is the scientific study of blood serum. In practice the term usually refers to the Diagnostic identification of antibodies in the serum These tests are based upon the ability of an antibody to bind specifically to an antigen. The antigen, usually a protein or carbohydrate made by an infectious agent, is bound by the antibody. This binding then sets off a chain of events that can be visibly obvious in various ways, dependent upon the test. For example, "Strep throat" is often diagnosed within minutes, and is based on the appearance of antigens made by the causative agent, S. pyogenes, that is retrieved from a patients throat with a cotton swab. Streptococcal pharyngitis or streptococcal sore throat ( Strep throat AmE) is a form of Group A streptococcal infection that affects the Streptococcus pyogenes is a spherical Gram-positive Bacteria that grows in long chains and is the cause of Group A streptococcal infections Serological tests, if available, are usually the preferred route of identification, however the tests are costly to develop and the reagents used in the test often require refrigeration. Refrigeration is the process of removing Heat from an enclosed space or from a substance and moving it to a place where it is unobjectionable Some serological methods are extremely costly, although when commonly used, such as with the "strep test", they can be inexpensive.
Technologies based upon the polymerase chain reaction (PCR) method will become nearly ubiquitous gold standards of diagnostics of the near future, for several reasons. First, the catalog of infectious agents has grown to the point that virtually all of the significant infectious agents of the human population have been identified. Second, an infectious agent must grow within the human body to cause disease; essentially it must amplify its own nucleic acids in order to cause a disease. This amplification of nucleic acid in infected tissue offers an opportunity to detect the infectious agent by using PCR. Third, the essential tools for directing PCR, primers, are derived from the genomes of infectious agents, and with time those genomes will be known, if they are not already. A primer is a strand of Nucleic acid that serves as a starting point for DNA replication. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby
Thus, the technological ability to detect any infectious agent rapidly and specifically are currently available. The only remaining blockades to the use of PCR as a standard tool of diagnosis are in its cost and application, neither of which is insurmountable. The diagnosis of a few diseases will not benefit from the development of PCR methods, such as some of the clostridial diseases (tetanus and botulism). The Clostridia are a class of Firmicutes, including Clostridium and other similar genera Tetanus is a medical condition that is characterized by a prolonged contraction of Skeletal muscle fibres Botulism ( Latin, botulus, "sausage" is a rare but serious Paralytic illness caused by Botulin Toxin. These diseases are fundamentally biological poisonings by relatively small numbers of infectious bacteria that produce extremely potent neurotoxins. A neurotoxin is a Toxin that acts specifically on nerve cells ( Neurons, usually by interacting with Membrane proteins such as Ion channels A significant proliferation of the infectious agent does not occur, this limits the ability of PCR to detect the presence of any bacteria.
Infection with most pathogens does not result in death of the host and the offending organism is ultimately cleared after the symptoms of the disease have waned.  This process requires immune mechanisms to kill or inactivate the inoculum of the pathogen. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor Inoculation is the placement of something to where it will grow or reproduce and is most commonly used in respect of the introduction of a serum Vaccine, or antigenic substance Specific acquired immunity against infectious diseases may be mediated by antibodies and/or T lymphocytes. Immunity is a material term that describes a state of having sufficient biological defenses to avoid Infection, Disease, or other unwanted biological invasion Antibodies (also known as immunoglobulins, abbreviated Ig) are Gamma globulin Proteins that are found in Blood or other Bodily T cells belong to a group of White blood cells known as Lymphocytes, and play a central role in Cell-mediated immunity. Immunity mediated by these two factors may be manifested by:
The immune response to a microorganism often causes symptoms such as a high fever and inflammation, and has the potential to be more devastating than direct damage caused by a microbe. Fever (also known as pyrexia, from the Greek pyretos meaning fire or a febrile response, from the Latin word Febris Inflammation ( Latin, inflamatio, to set on fire is the complex biological response of vascular tissues to harmful stimuli such as Pathogens
Resistance to infection (immunity) may be acquired following a disease, by asymptomatic carriage of the pathogen, by harboring an organism with a similar structure (crossreacting), or by vaccination. Immunity is a material term that describes a state of having sufficient biological defenses to avoid Infection, Disease, or other unwanted biological invasion An asymptomatic carrier ( healthy carrier or just carrier) is a person or other organism that has contracted an Infectious disease, but who displays no symptoms Vaccination is the administration of Antigenic material (the Vaccine) to produce immunity to a disease Knowledge of the protective antigens and specific acquired host immune factors is more complete for primary pathogens than for opportunistic pathogens.
Immune resistance to an infectious disease requires a critical level of either antigen-specific antibodies and/or T cells when the host encounters the pathogen. Some individuals develop natural serum antibodies to the surface polysaccharides of some agents although they have had little or no contact with the agent, these natural antibodies confer specific protection to adults and are passively transmitted to newborns. Blood plasma is the Liquid component of Blood, in which the Blood cells are suspended Polysaccharides are relatively complex Carbohydrates They are Polymers made up of many Monosaccharides joined together by Glycosidic bonds Passive immunity is the transfer of active Humoral immunity in the form of readymade antibodies from one individual to another
The World Health Organization collects information on global deaths by International Classification of Disease (ICD) code categories. The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify Diseases The following table lists the top infectious disease killers which caused more than 100,000 deaths in 2002 (estimated). 1993 data is included for comparison.
|Rank||Cause of death||Deaths 2002||Percentage of|
|Deaths 1993||1993 Rank|
|N/A||All infectious diseases||14. 7 million||25. 9%||16. 4 million||32. 2%|
|1||Lower respiratory infections||3. While often used as a synonym for Pneumonia, the rubric of lower respiratory tract infection can also be applied to other types of infection including Lung 9 million||6. 9%||4. 1 million||1|
|2||HIV/AIDS||2. Human immunodeficiency virus ( HIV) is a Lentivirus (a member of the Retrovirus family that can lead to acquired immunodeficiency syndrome 8 million||4. 9%||0. 7 million||7|
|3||Diarrheal diseases||1. Gastroenteritis (also known as gastro, gastric flu, and stomach flu, although unrelated to Influenza) is Inflammation of the 8 million||3. 2%||3. 0 million||2|
|4||Tuberculosis (TB)||1. Tuberculosis (abbreviated as TB for tubercle bacillus or T u' b' erculosis Bacillus --> is a common 6 million||2. 7%||2. 7 million||3|
|5||Malaria||1. Malaria is a vector -borne Infectious disease caused by Protozoan Parasites It is widespread in tropical and subtropical regions including 3 million||2. 2%||2. 0 million||4|
|6||Measles||0. Measles (rubeola is a Disease caused by a virus specifically a Paramyxovirus of the genus Morbillivirus. 6 million||1. 1%||1. 1 million||5|
|7||Pertussis||0. Pertussis, also known as whooping cough, is a highly contagious Disease caused by the Bacterium Bordetella pertussis; it derived its 29 million||0. 5%||0. 36 million||7|
|8||Tetanus||0. Tetanus is a medical condition that is characterized by a prolonged contraction of Skeletal muscle fibres 21 million||0. 4%||0. 15 million||12|
|9||Meningitis||0. Meningitis is Inflammation of the protective membranes covering the Brain and Spinal cord, known collectively as the Meninges. 17 million||0. 3%||0. 25 million||8|
|10||Syphilis||0. Syphilis is a Sexually transmitted disease caused by the spirochetal Bacterium Treponema pallidum pallidum. 16 million||0. 3%||0. 19 million||11|
|11||Hepatitis B||0. 10 million||0. 2%||0. 93 million||6|
|12-17||Tropical diseases (6)||0. Tropical diseases are diseases that are prevalent in or unique to tropical and subtropical regions 13 million||0. 2%||0. 53 million||9, 10, 16-18|
|Note: Other causes of death include maternal and perinatal conditions (5. 2%), nutritional deficiencies (0. 9%),|
noncommunicable conditions (58. 8%), and injuries (9. 1%).
The top three single agent/disease killers are HIV/AIDS, TB and malaria. Human immunodeficiency virus ( HIV) is a Lentivirus (a member of the Retrovirus family that can lead to acquired immunodeficiency syndrome Tuberculosis (abbreviated as TB for tubercle bacillus or T u' b' erculosis Bacillus --> is a common Malaria is a vector -borne Infectious disease caused by Protozoan Parasites It is widespread in tropical and subtropical regions including 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. Pertussis, also known as whooping cough, is a highly contagious Disease caused by the Bacterium Bordetella pertussis; it derived its Poliomyelitis, often called polio or infantile paralysis, is an acute viral Infectious disease spread from person to person primarily via Diphtheria ( Greek διφθερα ( diphthera)—“pair of leather scrolls" is an upper respiratory tract illness characterized by sore Measles (rubeola is a Disease caused by a virus specifically a Paramyxovirus of the genus Morbillivirus. Tetanus is a medical condition that is characterized by a prolonged contraction of Skeletal muscle fibres Children also make up a large percentage of lower respiratory and diarrheal deaths.
A pandemic (or global epidemic) is a disease that affects people over an extensive geographical area. A pandemic (from Greek παν pan all + δήμος demos people is an Epidemic of Infectious disease that spreads through In Epidemiology, an epidemic (from Greek epi- upon + demos people is a classification of a disease that appears as new cases in a
In most cases, microorganisms live in harmony with their hosts. Such is the case for many tropical viruses and the insects, monkeys, or other animals in which they have lived and reproduced. Because the microbes and their hosts have co-evolved, the hosts gradually become resistant to the microorganisms. In a broad sense biological co-evolution is "the change of a biological object triggered by the change of a related object" When a microbe jumps from a long-time animal host to a human being, it may cease to be a harmless parasite and become pathogenic. 
With most new infectious diseases, some human action is involved, changing the environment so that an existing microbe can take up residence in a new niche. When that happens, a pathogen that had been confined to a remote habitat appears in a new or wider region, or a microbe that had infected only animals suddenly begins to cause human disease. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually In Ecology, a niche (pronounced nich nēsh or nish A shorthand definition of niche is how an organism makes a living A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious
Abū Alī ibn Sīnā (Avicenna) discovered the contagious nature of infectious diseases in the early 11th century. TemplateInfobox Muslim scholars --> ( Persian /ابو علی الحسین ابن عبدالله ابن سینا (born A disease is an abnormal condition of an organism that impairs bodily functions and can be deadly He introduced quarantine as a means of limiting the spread of contagious and infectious diseases in The Canon of Medicine, circa 1020. For other uses see Quarantine (disambiguation Quarantine is voluntary or compulsory isolation typically to contain the spread of something The Canon of Medicine ( Arabic: القانون في الطب Al-Qanun fi al-Tibb " The Law of Medicine " Persian  He also stated that bodily secretion is contaminated by foul foreign earthly bodies before being infected, but he did not view them as primary causes of disease. Secretion is the process of segregating elaborating and releasing chemicals from a cell, or a secreted Chemical substance or amount of substance A disease is an abnormal condition of an organism that impairs bodily functions and can be deadly 
When the Black Death bubonic plague reached al-Andalus in the 14th century, Ibn Khatima and Ibn al-Khatib hypothesized that infectious diseases are caused by "contagious entities" which enter the human body. The Black Death, or the Black Plague, was one of the deadliest Pandemics in human history widely thought to have been caused by a bacterium named Yersinia Bubonic plague is the best-known manifestation of the bacterial disease plague, caused by the bacterium Yersinia pestis (formerly known as Al-Andalus (الأندلس was the Arabic name given to those parts of the Iberian Peninsula governed by Muslims or  Such ideas became more popular in Europe during the renaissance, particularly through the writing of the Italian monk Girolamo Fracastoro. The Renaissance (from French Renaissance, meaning "rebirth" Italian: Rinascimento, from re- "again" and nascere Girolamo Fracastoro ( Fracastorius) (1478‑ August 8, 1553) was an Italian Physician, Scholar (in Mathematics 
Anton van Leeuwenhoek (1632-1723) advanced the science of microscopy by being the first to observe microorganisms, allowing for easy visualization of bacteria. Antonie Philips van Leeuwenhoek (October 24 1632 &ndash August 30 1723 was a Dutch tradesman and Scientist from Delft, the Netherlands Microscopy is the technical field of using microscopes to view samples or objects
Louis Pasteur proved beyond doubt that certain diseases are caused by infectious agents, and developed a vaccine for rabies. Louis Pasteur (27 December 1822 – 28 September 1895 a French Chemist and Microbiologist, is best known for remarkable breakthroughs in the causes and Rabies (from rabies “madness rage fury” Also known as “ hydrophobia ” is a viral Zoonotic neuroinvasive disease that
Robert Koch, provided the study of infectious diseases with a scientific basis known as Koch's postulates. Heinrich Hermann Robert Koch ( December 11 1843 – May 27 1910) was a German Physician. Koch's postulates are four criteria designed to establish a causal relationship between a causative Microbe and a Disease.
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. Edward Jenner, FRS, ( May 17 1749 – January 26 1823) was an English scientist who studied his natural surroundings in Berkeley Jonas Edward Salk ( October 28 1914 &ndash June 23, 1995) was an American Biologist and Physician best Albert Bruce Sabin (August 26 1906 – March 3 1993 was an American medical researcher best-known for having developed an oral Polio vaccine. Smallpox is an Infectious disease unique to humans caused by either of two virus variants named Variola major and Variola minor. Poliomyelitis, often called polio or infantile paralysis, is an acute viral Infectious disease spread from person to person primarily via
Alexander Fleming discovered the world's first antibiotic Penicillin. Sir Alexander Fleming (6 August 1881 &ndash 11 March 1955 was a Scottish Biologist and Pharmacologist. In modern usage an antibiotic is a Chemotherapeutic agent with activity against Microorganisms such as Bacteria, fungi or Protozoa Penicillin (sometimes abbreviated PCN or pen) is a group of Beta-lactam antibiotics used in the treatment of Bacterial Infections
Gerhard Domagk develops Sulphonamides, the first broad spectrum synthetic antibacterial drugs. Gerhard Johannes Paul Domagk ( October 30, 1895 &ndash April 24, 1964) was a German Pathologist and Bacteriologist There are several sulfonamide-based groups of drugs The original antibacterial sulfonamides (sometimes called simply sulfa drugs are synthetic antimicrobial agents that contain the sulfonamide In Chemistry, chemical synthesis is purposeful execution of Chemical reactions in order to get a product, or several products
The medical treatment of infectious diseases falls into the medical field of Infectiology and in some cases the study of propagation pertains to the field of Epidemiology. Medicine is the art and science of healing It encompasses a range of Health care practices evolved to maintain and restore Human Health by the Epidemiology is the study of factors affecting the Health and Illness of populations and serves as the foundation and Logic of interventions made in the Generally, infections are initially diagnosed by primary care physicians or internal medicine specialists. An infection is the detrimental Colonization of a host Organism by a foreign Species. Primary care is a term used for the activity of a Health care provider who acts as a first point of consultation for all patients Internal medicine is the medical specialty concerned with the diagnosis management and nonsurgical treatment of unusual or serious diseases For example, an "uncomplicated" pneumonia will generally be treated by the internist or the pulmonologist (lung physician). Pneumonia is an inflammatory illness of the Lung. Frequently it is described as lung Parenchyma / alveolar inflammation and abnormal Internal medicine is the medical specialty concerned with the diagnosis management and nonsurgical treatment of unusual or serious diseases In Medicine, pulmonology (aka pneumology) is the specialty that deals with Diseases of the Lungs and the Respiratory tract. The work of the infectiologist therefore entails working with both patients and general practitioners, as well as laboratory scientists, immunologists, bacteriologists and other specialists. An infectious disease is a clinically evident Disease resulting from the presence of Pathogenic microbial agents including Pathogenic viruses Pathogenic Research is defined as Human activity based on Intellectual application in the investigation of Matter. Immunology is a broad branch of biomedical Science that covers the study of all aspects of the Immune system in all Organisms It deals with Microbiology (from Greek grc μῑκρος mīkros, "small" grc βίος bios, " Life " and grc -λογία .
An infectious disease team may be alerted when: