Microbiology Term Infection

Intertrigo is most commonly seen in chubby infants or obese adults. In the skin fold, heat, moisture, and rubbing produce erythema, maceration, or even erosions. Overgrowth of resident or transient flora may produce this problem. Acute infectious eczematoid dermatitis arises from a primary lesion such as a boil or a draining ear or nose, which are sources of infectious exudate. A hallmark of this disease is a streak of dermatitis along the path of flow of the discharge material.

Coagulase-positive staphylococci are the organisms most frequently isolated. Pseudofolliculitis of the beard, a common disorder, occurs most often in the beard area of black people who shave. The characteristic lesions are usually erythematous papules or, less commonly, pustules containing buried hairs. This occurs when a strongly curved hair emerging from curved hair follicles reenters the skin to produce an ingrown hair. Gram-positive microorganisms that belong to the resident flora are associated with this disorder—a clear illustration of the opportunism of nonpathogenic bacteria when the host defense is impaired.

The disease commonly referred to as athlete's foot has traditionally been regarded as strictly a fungal infection. This assumption has been revised, however, because fungi often cannot be recovered from the lesions throughout the disease course. Researchers now believe that the dermatophytes, the first invaders, cause skin damage that allows bacterial overgrowth, which promotes maceration and hyperkeratosis.

The fungi, through the production of antibiotics, then create an environment that favors the growth of certain coryneform bacteria and Brevibacterium. Proteolytic enzymes, which are produced by some of these bacteria, may aggravate the condition. If the feet become superhydrated, resident Gram-negative rods become the predominant flora, and the toe webs incur further damage. The fungi are then eliminated either by the action of antifungal substances of bacterial origin or by their own inability to compete for nutrients with the vigorously growing bacteria.

Localized skin tuberculosis may follow inoculation of Mycobacterium tuberculosis into a wound in individuals with no previous immunologic experience with the disease. The course starts as an inflammatory nodule chancre and is accompanied by regional lymphangitis and lymphadenitis. The course of the disease depends on the patient's resistance and the effectiveness of treatment. In an immune or partially immune host, two major groups of skin lesions are distinguished: Many cases of M marinum skin disease occur in children and adolescents who have a history of using swimming pools or cleaning fish tanks.

Often, there is a history of trauma, but even in the absence of trauma the lesions appear frequently on the sites most exposed to injury. The usually solitary lesions are tuberculoid granulomata that rarely show acid-fast organisms. The skin tuberculin test is positive. Lesions in M ulcerans skin disease occur most often on the arms or legs and occasionally elsewhere, but not on the palms or soles.

Most patients have a single, painless cutaneous ulcer with characteristic undermined edges. Geographic association of the disease with swamps and watercourses has been reported. In some tropical areas, chronic ulcers caused by this organism are common.

In scrofuloderma, tuberculosis of lymph nodes or bones is extended into the skin, resulting in the development of ulcers. A disseminated form of the disease occurs when bacteria are spread through the bloodstream in patients who have fulminating tuberculosis of the skin.

When hypersensitivity to tubercle bacilli is present, hematogenously disseminated antigen produces uninfected tuberculous skin lesions such as lichen scrofilloslls. There are several agents of actinomycetoma. About half of the cases are due to actinomycetes actinomycetoma ; the rest are due to fungi eumycetoma. The most common causes of mycetoma in the United States are Pseudallescheria Petriel lidium boydii a fungus and Actinomyces israelii a bacterium. Regardless of the organism involved, the clinical picture is the same.

Causative organisms are introduced into the skin by trauma. The disease is characterized by cutaneous swelling that slowly enlarges and becomes softer.

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Tunnel-like sinus tracts form in the deeper tissues, producing swelling and distortion, usually of the foot. The draining material contains granules of various sizes and colors, depending on the agent. Actinomyces israelii usually is the agent of human actinomycosis; Arachnia propionica Actinomyces propinicus is the second most common cause. The characteristic appearance of the lesion is a hard, red, slowly developing swelling. The hard masses soften and eventually drain, forming chronic sinus tracts with little tendency to heal.

In about 50 percent of cases, the initial lesion is cervicofacial, involving the tissues of the face, neck, tongue, and mandible. About 20 percent of cases show thoracic actinomycosis, which may result from direct extension of the disease from the neck or from the abdomen or as a primary infection from oral aspiration of the organism.

In abdominal actinomycosis, the primary lesion is in the cecum, the appendix, or the pelvic organs. Debriding superficial pyoderma and then repeatedly cleansing the exposed lesions with topical antiseptics such as chlorhexidine removes the source of infection and minimizes its spread to adjacent skin sites or to other patients.

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Many secondary superficial skin infections, such as the web infections, will clear with simple twice-daily cleansing. For foot infections, the patient should wear open shoes or sandals, which permit air circulation. Aluminum chloride, a drying agent, inhibits overgrowth of opportunistic bacteria in foot, perineal, and axillary areas. Topical antibiotics contain a combination of neomycin, bacitracin, and polymyxin.

Some newer preparations contain mupirocin, gramicidin, or erythromycin, and others combine these antibiotics with steroids. For an informed, cooperative patient suffering only minimal disease, topical antibiotics are often preferred to oral antibiotics because of the adverse reactions associated with systemic therapy. Systemic treatment with antibiotics is mandatory for extensive pyoderma.

Systemic antibiotics can be administered orally or parenterally. Oral therapy is sufficient for most extensive dermal infections, but the parenteral route is preferred for severe infections. A wide range of antibiotics for systemic therapy of pyoderma is available Table The choice of a specific antibiotic should be based on two factors: In this costconscious world one must also relate efficacy to consumer cost. Many less expensive antibiotics are just as effective against a given pathogen as the most expensive drugs with wider spectra. Viral skin diseases can produce both localized and generalized skin infections Table Viruses from several major groups cause skin lesions.

Herpes simplex virus infection is probably the most common viral skin disease see Ch. Almost the entire adult population has had herpes simplex at one time or another. Herpes simplex virus, a DNA virus, is the agent. There are two types of herpes simplex virus. Type 1 is usually associated with nongenital lesions, whereas type 2 is recovered from genital lesions. The incidence of type 1 genital infections in young patients has recently increased.

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The viruses that cause smallpox, vaccinia, and cowpox are closely related; all are large DNA viruses see Ch. The smallpox virus is now extinct. Cowpox virus causes an infection of cattle that is acquired by handling infected animals.

Vaccinia viruses are vaccine strains developed in the laboratory and adapted to grow in the skin of humans, rabbits, and calves. Several clinical manifestations may occur in individuals who were vaccinated against smallpox with vaccinia virus. The main problem with vaccinia virus arose when it became desirable to vaccinate a person already suffering from eczema or other skin diseases. Vaccination may produce eczema vaccinatum. Molluscum contagiosum also is caused by a poxvirus and is characterized by numerous small, pink nodules, most often on the face, genitalia, or the rectal area.

Lesions also occur on the back, arms, buttocks, and inner thighs. The disease is generally harmless and self-limiting. Human papillomaviruses cause warts see Ch.

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Verruca vulgaris occurs commonly on hands and fingers as single or multiple lesions. These warts are generally painless, firm, dry, and rough. They may remain stable or regress spontaneously. Verruca plantaris plantar wart is a clinical variety of verruca vulgaris that occurs on the sole of the foot.

During standing, walking, and running, these warts push into the skin and may be painful. Genital warts appear as large lesions of red, soft masses that may coalesce. Verruca plana juvenilis also known as juvenile flat warts occurs most commonly in children. The lesions are in groups and may appear on the face, neck, back of the hands, and arms. These warts may also occur in adults. Because of the limited number of effective antiviral agents, prevention is important.

Oral and intravenous acyclovir is effective for treatment of primary herpesvirus infection and for recurrent genital herpes and herpes zoster in immunosuppressed persons. Several genera of fungi are responsible for diseases of the skin. This group of fungi, known collectively as dermatophytes, is discussed in the chapters on mycology.

Some nondermatophytes, including yeasts, can also cause skin infections. The nail consists of four epidermal components: The matrix is close to the bony phalanx. The horny end product of the matrix is the nail plate, which migrates distally over the nailbed. The distal portion of the matrix, the lunula, is visible as a white, crescent-shaped structure.

The proximal nailfold is a modified extension of the epidermis of the dorsum of the finger, which forms a fold over the matrix; its horny end product is the cuticle. The nailbed is an epidermal structure that begins at the distal margin of the lunula and terminates in the hyponychium, which is the extension of the volar epidermis under the nail plate. It ends adjacent to the nailbed.

Onychomycoses are infections of the nails by fungi. Universally recognized agents of these diseases are species of Trichophyton, Microsporum rarely , and Epidermophyton Table These dermatophytes are commonly called ringworm fungi. Nondermatophytic fungi also occasionally cause onychomycoses, but usually cause only toenail problems; they rarely affect the fingernails.

Distal subungual onychomycosis primarily involves the distal nailbed and hyponychium, with secondary involvement of the underside of the nail plate. Trichophyton rubrum is one of the organisms that cause this clinical type. White superficial onychomycosis involves the toenail plate on the surface of the nail.

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It is caused by T mentagrophytes and by species of Cephalosporium, Aspergillus, and Fusarium. Proximal subungual onychomycosis is an invasion of the nail plate from the proximal nailfold producing a specific nail condition. It is caused by T rubrum and T megninii. This is a rare type of onychomycosis, but in patients with AIDS proximal white subungual onychomycosis is common.

Candida onychomycosis involves all of the nail plate. It is caused by C albicans and is seen in patients who have chronic cutaneous candidiasis, a syndrome associated with cellular and humoral immune abnormalities. Superficial types of onychomycosis may be successfully treated. Mechanical scraping of the chalky white material on the nail plate and application of topical antifungal agents such as miconazole, ciclopirox olamine, or clotrimazole are recommended. Newer therapeutic nail lacquers are being tested in the United States. Distal subungual and proximal subungual onychomycosis infections are much more difficult to treat.

Oral griseofulvin may be required to bring about clearing of the fingernail. For toenails with extensive involvement, oral itraconazole, fluconazole and terbinafine are effective. No oral or topical medication is effective in eliminating nondermatophyte mold infection of the nails. Pseudomonas aeruginosa is associated with green nail syndrome, which is essentially a greenish discoloration of the nail plate. Attempts to culture Pseudomonas from the deep section of the nail have not been successful; however, P aeruginosa has been isolated on cultures of specimens from the paronychia inflammatory lesion around the margin of a nail.

Whether there is true invasion of the nail plate by the bacteria or just diffusion of the pigment into the nail plate is not certain. Black paronychia is associated with Proteus species. Staphylococci and streptococci may be found as secondary invaders. Turn recording back on. National Center for Biotechnology Information , U. Show details Baron S, editor. University of Texas Medical Branch at Galveston ; General Concepts Etiology Skin diseases can be caused by viruses, bacteria, fungi, or parasites. Clinical Manifestations Most skin infections cause erythema, edema, and other signs of inflammation.

Prevention and Treatment Cleansing and degerming the skin with a soap or detergent containing an antimicrobial agent may be useful. Introduction Skin diseases are caused by viruses, rickettsiae, bacteria, fungi, and parasites. Skin Infections Skin infections may be either primary or secondary Fig.

Figure Spread of infections to skin. Methods for Laboratory Diagnosis Specimen Collection Bacteria Specimens are collected with a blade or by swabbing the involved areas of the skin. Viruses Vesicles are cleaned with 70 percent alcohol followed by sterile saline. Fungi Cutaneous samples are obtained by scraping skin scales or infected nails into a sterile Petri dish or a clean envelope. Cultures Most pathogenic skin bacteria grow on artificial media, and selection of the medium is important.

Bacterial Skin Infections The classification of bacterial skin infections pyodermas is an attempt to integrate various clinical entities in an organized manner. Primary Infections Impetigo Three forms of impetigo are recognized on the basis of clinical, bacteriologic, and histologic findings. Cellulitis and Erysipelas Streptococcus pyogenes is the most common agent of cellulitis, a diffuse inflammation of loose connective tissue, particularly subcutaneous tissue.

Staphylococcal Scalded Skin Syndrome Staphylococcal scalded skin syndrome SSSS , also called Lyell's disease or toxic epidermal necrolysis, starts as a localized lesion, followed by widespread erythema and exfoliation of the skin. Folliculitis Folliculitis can be divided into two major categories on the basis of histologic location: Erysipeloid Erysipeloid, a benign infection that occurs most often in fishermen and meat handlers, is characterized by redness of the skin usually on a finger or the back of a hand , which persists for several days.

Pitted Keratolysis Pitted keratolysis is a superficial infection of the plantar surface, producing a punched-out appearance. Erythrasma Erythrasma is a chronic, superficial infection of the pubis, toe web, groin, axilla, and inframammary folds. Trichomycosis Trichomycosis involves the hair in the axillary and pubic regions and is characterized by development of nodules of varying consistency and color. Secondary Infections Intertrigo Intertrigo is most commonly seen in chubby infants or obese adults.

Acute Infectious Eczematoid Dermatitis Acute infectious eczematoid dermatitis arises from a primary lesion such as a boil or a draining ear or nose, which are sources of infectious exudate. Pseudofolliculitis of the Beard Pseudofolliculitis of the beard, a common disorder, occurs most often in the beard area of black people who shave. Toe Web Infection The disease commonly referred to as athlete's foot has traditionally been regarded as strictly a fungal infection.

Other Bacterial Skin Diseases Skin Tuberculosis Localized Form Localized skin tuberculosis may follow inoculation of Mycobacterium tuberculosis into a wound in individuals with no previous immunologic experience with the disease. Mycobacterium marinum Skin Disease Many cases of M marinum skin disease occur in children and adolescents who have a history of using swimming pools or cleaning fish tanks.

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Mycobacterium ulcerans Skin Disease Lesions in M ulcerans skin disease occur most often on the arms or legs and occasionally elsewhere, but not on the palms or soles. Actinomycetoma There are several agents of actinomycetoma. Actinomycosis Actinomyces israelii usually is the agent of human actinomycosis; Arachnia propionica Actinomyces propinicus is the second most common cause.

Treatment of the Pyodermas General Considerations Debriding superficial pyoderma and then repeatedly cleansing the exposed lesions with topical antiseptics such as chlorhexidine removes the source of infection and minimizes its spread to adjacent skin sites or to other patients. Topical Treatment Topical antibiotics contain a combination of neomycin, bacitracin, and polymyxin. Systemic Therapy Systemic treatment with antibiotics is mandatory for extensive pyoderma. The isolation of enzymes from infected tissue can also provide the basis of a biochemical diagnosis of an infectious disease.

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. 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.

Serological methods are highly sensitive, specific and often extremely rapid tests used to identify microorganisms. 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. 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. Some serological methods are extremely costly, although when commonly used, such as with the "strep test", they can be inexpensive.

Complex serological techniques have been developed into what are known as Immunoassays. Immunoassays can use the basic antibody — antigen binding as the basis to produce an electro-magnetic or particle radiation signal, which can be detected by some form of instrumentation. Signal of unknowns can be compared to that of standards allowing quantitation of the target antigen. To aid in the diagnosis of infectious diseases, immunoassays can detect or measure antigens from either infectious agents or proteins generated by an infected organism in response to a foreign agent. For example, immunoassay A may detect the presence of a surface protein from a virus particle.

Immunoassay B on the other hand may detect or measure antibodies produced by an organism's immune system that are made to neutralize and allow the destruction of the virus. Instrumentation can be used to read extremely small signals created by secondary reactions linked to the antibody — antigen binding. Instrumentation can control sampling, reagent use, reaction times, signal detection, calculation of results, and data management to yield a cost effective automated process for diagnosis of infectious disease.

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. 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. These diseases are fundamentally biological poisonings by relatively small numbers of infectious bacteria that produce extremely potent neurotoxins.

A significant proliferation of the infectious agent does not occur, this limits the ability of PCR to detect the presence of any bacteria. Given the wide range of bacteria, viruses, and other pathogens that cause debilitating and life-threatening illness, the ability to quickly identify the cause of infection is important yet often challenging.

For example, more than half of cases of encephalitis , a severe illness affecting the brain, remain undiagnosed, despite extensive testing using state-of-the-art clinical laboratory methods. Metagenomics is currently being researched for clinical use, and shows promise as a sensitive and rapid way to diagnose infection using a single all-encompassing test.

This test is similar to current PCR tests; however, amplification of genetic material is unbiased rather than using primers for a specific infectious agent. This amplification step is followed by next-generation sequencing and alignment comparisons using large databases of thousands of organismic and viral genomes. Metagenomic sequencing could prove especially useful for diagnosis when the patient is immunocompromised. An ever-wider array of infectious agents can cause serious harm to individuals with immunosuppression, so clinical screening must often be broader. Additionally, the expression of symptoms is often atypical, making clinical diagnosis based on presentation more difficult.

Thirdly, diagnostic methods that rely on the detection of antibodies are more likely to fail. A broad, sensitive test for pathogens that detects the presence of infectious material rather than antibodies is therefore highly desirable. There is usually an indication for a specific identification of an infectious agent only 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 s, 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. 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.

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.

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.

Techniques like hand washing, wearing gowns, and wearing face masks can help prevent infections from being passed from one person to another. Aseptic technique was introduced in medicine and surgery in the late 19th century and greatly reduced the incidence of infections caused by surgery. Frequent hand washing remains the most important defense against the spread of unwanted organisms. Cooking foods well and avoiding foods that have been left outside for a long time is also important.

General Concepts

Antimicrobial substances used to prevent transmission of infections include:. One of the ways to prevent or slow down the transmission of infectious diseases is to recognize the different characteristics of various diseases. The human strains of Ebola virus, for example, incapacitate their victims extremely quickly and kill them soon after. As a result, the victims of this disease do not have the opportunity to travel very far from the initial infection zone.

Thus, the initial stage of Ebola is not very contagious since its victims experience only internal hemorrhaging. As a result of the above features, the spread of Ebola is very rapid and usually stays within a relatively confined geographical area. Also, the relatively low virulence allows its victims to travel long distances, increasing the likelihood of an epidemic. Another effective way to decrease the transmission rate of infectious diseases is to recognize the effects of small-world networks. 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. 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.

A general method to prevent transmission of vector -borne pathogens is pest control. 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. Immunity mediated by these two factors may be manifested by:. The immune system 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.

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. Knowledge of the protective antigens and specific acquired host immune factors is more complete for primary pathogens than for opportunistic pathogens. There is also the phenomenon of herd immunity which offers a measure of protection to those otherwise vulnerable people when a large enough proportion of the population has acquired immunity from certain infections.

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. The organism that is the target of an infecting action of a specific infectious agent is called the host. The host harbors and agent in a mature, or sexually active stage phase called the definitive host. The intermediate host comes in contact during the larvae stage.

A host can be anything living and can attain to asexual and sexual reproduction. For instance, for genotype 1 hepatitis C treated with Pegylated interferon-alpha-2a or Pegylated interferon-alpha-2b brand names Pegasys or PEG-Intron combined with ribavirin , it has been shown that genetic polymorphisms near the human IL28B gene, encoding interferon lambda 3, are associated with significant differences in the treatment-induced clearance of the virus.

This finding, originally reported in Nature, [33] showed that genotype 1 hepatitis C patients carrying certain genetic variant alleles near the IL28B gene are more possibly to achieve sustained virological response after the treatment than others. Later report from Nature [34] demonstrated that the same genetic variants are also associated with the natural clearance of the genotype 1 hepatitis C virus. When infection attacks the body, anti-infective drugs can suppress the infection. Several broad types of anti-infective drugs exist, depending on the type of organism targeted; they include antibacterial antibiotic ; including antitubercular , antiviral , antifungal and antiparasitic including antiprotozoal and antihelminthic agents.

Depending on the severity and the type of infection, the antibiotic may be given by mouth or by injection, or may be applied topically. Severe infections of the brain are usually treated with intravenous antibiotics. Sometimes, multiple antibiotics are used in case there is resistance to one antibiotic. Antibiotics only work for bacteria and do not affect viruses. Antibiotics work by slowing down the multiplication of bacteria or killing the bacteria.

The most common classes of antibiotics used in medicine include penicillin , cephalosporins , aminoglycosides , macrolides , quinolones and tetracyclines. Not all infections require treatment, and for many self-limiting infections the treatment may cause more side-effects than benefits. Antimicrobial stewardship is the concept that healthcare providers should treat an infection with an antimicrobial that specifically works well for the target pathogen for the shortest amount of time and to only treat when there is a known or highly suspected pathogen that will respond to the medication.

In , about 10 million people died of infectious diseases. The following table lists the top infectious disease by number of deaths in Childhood diseases include pertussis , poliomyelitis , diphtheria , measles and tetanus. Children also make up a large percentage of lower respiratory and diarrheal deaths. In , approximately 3. A pandemic or global epidemic is a disease that affects people over an extensive geographical area. 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. Several human activities have led to the emergence of zoonotic human pathogens, including viruses, bacteria, protozoa, and rickettsia, [52] and spread of vector-borne diseases, [51] see also globalization and disease and wildlife disease:. Ideas of contagion became more popular in Europe during the Renaissance , particularly through the writing of the Italian physician Girolamo Fracastoro.

Anton van Leeuwenhoek — advanced the science of microscopy by being the first to observe microorganisms, allowing for easy visualization of bacteria. In the midth 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.

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.

The medical treatment of infectious diseases falls into the medical field of Infectious Disease and in some cases the study of propagation pertains to the field of Epidemiology. Generally, infections are initially diagnosed by primary care physicians or internal medicine specialists. For example, an "uncomplicated" pneumonia will generally be treated by the internist or the pulmonologist lung physician. The work of the infectious diseases specialist therefore entails working with both patients and general practitioners, as well as laboratory scientists , immunologists , bacteriologists and other specialists.

A number of studies have reported associations between pathogen load in an area and human behavior. Higher pathogen load is associated with decreased size of ethnic and religious groups in an area. This may be due high pathogen load favoring avoidance of other groups, which may reduce pathogen transmission, or a high pathogen load preventing the creation of large settlements and armies that enforce a common culture.

Higher pathogen load is also associated with more restricted sexual behavior, which may reduce pathogen transmission. It also associated with higher preferences for health and attractiveness in mates. Higher fertility rates and shorter or less parental care per child is another association that may be a compensation for the higher mortality rate. There is also an association with polygyny which may be due to higher pathogen load, making selecting males with a high genetic resistance increasingly important.

Higher pathogen load is also associated with more collectivism and less individualism, which may limit contacts with outside groups and infections. There are alternative explanations for at least some of the associations although some of these explanations may in turn ultimately be due to pathogen load. Thus, polygny may also be due to a lower male: Another example is that poor socioeconomic factors may ultimately in part be due to high pathogen load preventing economic development. Evidence of infection in fossil remains is a subject of interest for paleopathologists , scientists who study occurrences of injuries and illness in extinct life forms.

Signs of infection have been discovered in the bones of carnivorous dinosaurs. When present, however, these infections seem to tend to be confined to only small regions of the body. A skull attributed to the early carnivorous dinosaur Herrerasaurus ischigualastensis exhibits pit-like wounds surrounded by swollen and porous bone. The unusual texture of the bone around the wounds suggests they were afflicted by a short-lived, non-lethal infection.

Scientists who studied the skull speculated that the bite marks were received in a fight with another Herrerasaurus. Other carnivorous dinosaurs with documented evidence of infection include Acrocanthosaurus , Allosaurus , Tyrannosaurus and a tyrannosaur from the Kirtland Formation. The infections from both tyrannosaurs were received by being bitten during a fight, like the Herrerasaurus specimen. A Space Shuttle experiment found that Salmonella typhimurium , a bacterium that can cause food poisoning , became more virulent when cultivated in space.

From Wikipedia, the free encyclopedia. For the medical specialty, see Infectious disease medical specialty. For other uses, see Infection disambiguation. Effect of spaceflight on the human body , Medical treatment during spaceflight , and Space medicine. Bioinformatics Resource Centers for Infectious Diseases Biological hazard Blood-borne disease Coinfection Copenhagen Consensus Cordon sanitaire Disease diffusion mapping Foodborne illness Gene therapy History of medicine Hospital-acquired infection Eradication of infectious diseases Human Microbiome Project Infection control Isolation health care List of bacterial vaginosis microbiota List of causes of death by rate List of diseases caused by insects List of epidemics List of infectious diseases Mathematical modelling of infectious disease Membrane vesicle trafficking Multiplicity of infection Neglected tropical diseases Social distancing Spatiotemporal Epidemiological Modeler STEM Spillover infection Threshold host density Transmission medicine Ubi pus, ibi evacua Latin: Retrieved 21 November Association of American Medical Colleges.

Archived from the original on Infectious disease is the subspecialty of internal medicine dealing with the diagnosis and treatment of communicable diseases of all types, in all organs, and in all ages of patients. Medical Microbiology Fourth Edition: University of Texas Medical Branch at Galveston. Archived from the original on June 29, Sherris Medical Microbiology 4th ed.

Golden; Fred Peterson The Truth About Illness and Disease. Archived from the original on March 5, Retrieved 4 July Clamydia trachonmatis and Genital Mycoplasmias: Pathogens with an Impact on Human Reproductive Health". American Journal of Infection Control. Journal of Epidemiology and Community Health. Current Opinion in Infectious Diseases. North Carolina Digital History. National Center for Biotechnology Information. Archived June 1, , at the Wayback Machine.

Centers for Disease Control and Prevention. Archived March 9, , at the Wayback Machine. Infectious Diseases Transmissible from Animals to Humans 3rd ed. Hyatt 27 January J R Soc Med. Mesozoic Vertebrate Life , edited by Tanke, D. Retrieved 14 September Advances in Space Research.