{ "id": "pathogen", "title": "Pathogen", "lang": "en", "source_lang": "en", "summary": "A biological agent capable of causing disease in a susceptible host.", "category": "science", "subcategory": "biology", "type": "concept", "aliases": [ "Infectious agent", "Disease-causing agent" ], "generated_at": "2026-10-22", "model": "pro/gpt-6.1-sol", "url": "https://aiwiki.page/en/pathogen/", "translations": { "zh-Hans": { "url": "https://aiwiki.page/zh/pathogen/", "json": "https://aiwiki.page/zh/pathogen.json" } }, "sections": [ { "heading": "", "text": "A pathogen is a biological agent capable of causing infectious disease in a host. Pathogens include certain bacteria, viruses, fungi, protozoa, and parasitic worms, as well as unconventional infectious agents such as prions. The term describes a disease-causing relationship rather than a single taxonomic group: an agent’s effects depend on its biological properties, the host’s susceptibility, and the circumstances of exposure. Infection therefore does not invariably result in disease, and many microorganisms are harmless or beneficial in their usual environments. (ncbi.nlm.nih.gov)\n\nPathogens affect humans, other animals, and plants, linking medicine and public health with agriculture and ecology. Understanding them requires examining how they enter hosts, obtain resources, evade defenses, cause damage, and move between hosts or environmental reservoirs. Their identification and control draw on laboratory diagnosis, epidemiology, immunology, and genomic surveillance, while antimicrobial resistance and cross-species transmission connect pathogen biology to the wider relationships among human, animal, plant, and environmental health. (apsnet.org)" }, { "heading": "Definition, Scope, and Terminology", "text": "A pathogen is a biological agent capable of causing disease in a host. The term describes a functional relationship, not a category in taxonomy: agents belonging to unrelated biological groups can be pathogens, while closely related organisms may differ in their ability to cause disease. Nor is “pathogen” synonymous with microorganism; many microorganisms do not cause disease, and some pathogens, including parasitic worms, are multicellular animals. Human medicine, veterinary medicine, and plant pathology apply the term to disease-causing agents of their respective hosts. In plant science, infectious diseases caused by pathogens are distinguished from disorders caused by nonliving factors such as nutrient imbalance, pollutants, or unsuitable environmental conditions. (ncbi.nlm.nih.gov)\n\nContamination, colonization, infection, and infectious disease describe different relationships between an agent and its surroundings or host. Contamination means that an agent is present on a surface, object, food, or specimen; it does not establish that the agent has become established in a host. Colonization generally denotes microbial establishment on or in the body without attributable disease—for example, carriage of Staphylococcus aureus on the skin or in the nose. Infection involves establishment and multiplication of an infectious agent in a host, but may remain asymptomatic. Infectious disease occurs when infection produces pathological changes or clinical illness. These categories are not necessarily successive stages, and terminology varies somewhat among disciplines. The essential distinction is that detecting an agent does not, by itself, demonstrate that it caused a particular illness: harmless carriage, asymptomatic infection, and contamination must be distinguished from disease causation. (cdc.gov)\n\nPathogenicity is the capacity to cause disease; virulence describes the relative degree of disease or damage produced in a specified host and setting. These properties depend on the host–agent interaction rather than on the agent alone. Dose, route of entry, host defenses, and the outcome being measured therefore matter when comparing agents or strains. In epidemiology, the terms also have operational meanings: pathogenicity can be expressed as the proportion of infected individuals who develop clinical disease, whereas virulence can be expressed as the proportion of clinical cases that become severe or fatal. These measures answer different questions and should not be confused with how efficiently an agent spreads. Pathogenesis, by contrast, denotes the processes through which disease develops. (ncbi.nlm.nih.gov)\n\nOpportunistic pathogenicity is disease-causing capacity expressed particularly when host defenses are impaired or an organism reaches a normally protected anatomical site. Organisms ordinarily tolerated as resident microbes may consequently act as pathogens. For example, intestinal microbes entering the abdominal cavity after bowel perforation can cause peritonitis, although their presence within the intestinal lumen does not itself constitute disease. “Opportunistic” thus identifies the circumstances that permit disease, not a separate taxonomic group or an assurance that the resulting illness is mild. (ncbi.nlm.nih.gov)\n\nA pathogen must also be distinguished from a vector, a living intermediary that transmits an agent, and a reservoir, the host population or environmental habitat in which an agent normally persists and, where applicable, multiplies. These terms identify different roles in transmission rather than interchangeable names for the disease-causing agent. Infection is likewise distinct from intoxication by a preformed microbial toxin. In staphylococcal food poisoning, S. aureus multiplies in food and produces enterotoxin before ingestion; illness does not require the bacterium to establish an infection in the person eating it. Symptoms typically begin within 30 minutes to 8 hours. Cooking may kill the bacteria without destroying the toxin already present, illustrating why microbial origin does not make every toxin-mediated illness an infection. (cdc.gov)" }, { "heading": "Major Groups of Pathogens", "text": "Pathogenic bacteria are cellular prokaryotes: they lack a membrane-bound nucleus but possess their own ribosomes and metabolic machinery and generally reproduce by binary fission. Their disease-causing properties vary both between species and among strains of the same species. Mycobacterium tuberculosis, for example, is the principal bacterial cause of tuberculosis. By contrast, most *Escherichia coli* are harmless inhabitants of the intestinal tract, whereas particular strains cause disease. Shiga toxin-producing E. coli, including pathogenic O157:H7 strains, carry toxin genes that distinguish them from harmless intestinal strains. Thus, identification at the species level does not always establish whether a bacterial isolate is pathogenic. (ncbi.nlm.nih.gov)\n\nViruses are acellular infectious agents whose genomes consist of DNA or RNA. A complete virus particle, or virion, contains a genome enclosed in a protein capsid; some viruses also have a lipid envelope bearing viral proteins. Unlike cellular pathogens, viruses lack ribosomes and cannot independently manufacture the proteins required to produce progeny. Replication therefore requires entry into a compatible host cell and use of its biosynthetic machinery, together with virus-encoded components. New genomes and structural proteins are assembled into particles rather than produced by division of a parent cell. Viral genomes may be single-stranded or double-stranded and may comprise one molecule or several segments, providing substantial organizational diversity within this group. (ncbi.nlm.nih.gov)\n\nPathogenic fungi are eukaryotes, with nuclei and intracellular organization distinct from those of bacteria. They include unicellular yeasts and filamentous molds; some change form under different environmental conditions. Histoplasma capsulatum, for example, grows as a mold in soil but adopts a yeast form in infected tissues. Protozoan parasites are also unicellular eukaryotes, including Plasmodium, the agents of malaria, and the intestinal parasite Entamoeba histolytica. Helminths, in contrast, are multicellular parasitic animals, including roundworms, tapeworms, and flukes. Their eggs or larvae may be microscopic even when adults are readily visible: adult Ascaris can reach approximately 30 cm. Consequently, “pathogen” is not synonymous with microorganism. (ncbi.nlm.nih.gov)\n\nPlant pathogens include bacteria, viruses, true fungi, oomycetes, and plant-parasitic nematodes. Oomycetes resemble fungi in their filamentous growth and absorptive nutrition but belong to a different evolutionary lineage, more closely related to brown algae. Their walls are generally rich in glucans and cellulose rather than the chitin characteristic of fungal walls, and their vegetative stages are usually diploid. Phytophthora infestans, which causes potato and tomato late blight, is an oomycete rather than a true fungus. Plant-parasitic nematodes are animals: many use a needlelike feeding structure called a stylet to puncture plant cells. Root-knot nematodes, Meloidogyne species, establish specialized feeding sites in roots and induce characteristic galls. (apsnet.org)\n\nViroids are plant-infecting agents consisting of small, circular, single-stranded RNA molecules without a protein capsid. They do not encode proteins and depend on host enzymes for replication, but do not require a helper virus. Theodor O. Diener introduced the term in 1971 for the agent of potato spindle tuber disease; the extensively studied potato spindle tuber viroid RNA contains 359 nucleotides. These features distinguish viroids from viruses, whose genomes encode proteins and are packaged into particles. (apsnet.org)\n\nPrions differ from all nucleic-acid-based pathogens: their infectious activity resides in misfolded protein rather than a DNA or RNA genome. A disease-associated conformation of the host prion protein promotes conversion of normally folded molecules into abnormal forms, enabling propagation without genome replication. Prions cause transmissible spongiform encephalopathies, including Creutzfeldt–Jakob disease in humans and bovine spongiform encephalopathy in cattle. Their protein-based propagation distinguishes them from both viruses and viroids. (ncbi.nlm.nih.gov)" }, { "heading": "Development of the Pathogen Concept", "text": "The nineteenth-century establishment of germ theory depended on experiments distinguishing microbial activity from spontaneous generation and linking particular organisms to particular diseases. In experiments described in his 1862 memoir, Louis Pasteur boiled liquids in swan-necked flasks whose curved necks admitted air but trapped dust and its microorganisms. The liquids remained unaltered while protected from those particles, showing that exposure to air alone did not generate microbial life. These experiments established a basis for studying contamination, rather than directly identifying a disease agent. Robert Koch supplied more disease-specific evidence: his 1876 anthrax investigations linked the disease to Bacillus anthracis and demonstrated its resistant spore stage. On March 24, 1882, he presented his identification of the bacterium responsible for tuberculosis. (pasteur.fr)\n\nThe experimental logic associated with Koch became codified as Koch’s postulates, conventionally presented as four requirements. The suspected microorganism should be associated with cases of the disease and absent from healthy hosts; it should be isolated and grown in pure culture; the cultured organism should reproduce the disease when introduced into a healthy, susceptible experimental host; and the same organism should be recovered from that host. Isolation separated the candidate agent from other components of diseased material, experimental inoculation tested its causal capacity, and recovery checked that the resulting illness involved the original agent. The sequence therefore went beyond observing microorganisms in damaged tissues: it connected association, controlled intervention, and reproducibility. (ncbi.nlm.nih.gov)\n\nLiteral application proved too restrictive. Asymptomatic infection and carriage contradict the requirement that a pathogen be absent from healthy individuals; host susceptibility also means that exposure need not produce disease in every infected host. Some agents cannot be maintained in cell-free pure culture, while viruses require living cells for replication. Experimental reproduction of serious human disease may be ethically unacceptable, and an appropriate animal model may not exist. These limitations concern the applicability of the tests, not whether such agents can cause disease. In 1996, David N. Fredricks and David A. Relman proposed sequence-based criteria that retained the emphasis on causal evidence, including preferential detection of microbial sequences in diseased tissue, correspondence between sequence abundance and disease course, and localization consistent with tissue pathology. (ncbi.nlm.nih.gov)\n\nResearch on tobacco mosaic disease expanded the concept beyond readily cultured bacteria. In 1892, Dmitri Ivanovsky reported that infectious plant sap remained infectious after passage through porcelain filters intended to retain bacteria. In 1898, Martinus Beijerinck extended these findings, interpreting the agent as a distinct infectious entity that multiplied in living plant tissue rather than ordinary culture media. Such experiments helped establish viruses as a separate class of agents. Molecular genetics subsequently shifted causal experimentation to individual microbial genes. Stanley Falkow’s 1988 molecular postulates asked whether a suspected virulence trait was associated with pathogenic strains, whether specifically inactivating its gene reduced virulence, and whether restoring gene function restored the phenotype. This approach tested contributions to pathogenicity rather than requiring every gene in a pathogen to be disease-causing. (apsnet.org)\n\nInfectious proteins challenged a further assumption: that every transmissible biological agent must possess a nucleic-acid genome. In 1982, Stanley B. Prusiner introduced the term prion for the scrapie agent. His report described evidence that protein was required for infectivity, including sensitivity to protein-destroying treatments, whereas several treatments targeting nucleic acids failed to abolish infectivity. Prion research established a mechanism in which an abnormal protein conformation promotes conversion of the host’s corresponding protein, rather than propagation through an agent-specific DNA or RNA genome. Prusiner received the 1997 Nobel Prize in Physiology or Medicine for this discovery. (pubmed.ncbi.nlm.nih.gov)" }, { "heading": "Host Range and Susceptibility", "text": "A pathogen’s host range comprises the species it can infect; tissue tropism describes its preference for particular tissues or cell types within a host. Both depend on biological compatibility rather than exposure alone. A suitable host must provide accessible nutrients, appropriate physiological conditions, and, for intracellular agents, cellular machinery that supports replication. Receptor recognition can restrict entry, but does not by itself guarantee productive infection. In 1989, Cathy L. Mendelsohn, Eckard Wimmer, and Vincent R. Racaniello cloned the human poliovirus receptor, now called CD155. They found receptor transcripts in more tissues than displayed functional virus-binding sites, demonstrating that receptor-gene expression alone could not explain the virus’s restricted tropism. (ncbi.nlm.nih.gov)\n\nSusceptibility also depends on the conditions encountered at a particular body site. Nutritional compatibility and temperature influence whether an organism can multiply, while local clearance mechanisms can prevent establishment even where nutrients are available. In cystic fibrosis, impaired clearance of respiratory mucus favors infection by mucoid strains of Pseudomonas aeruginosa. This illustrates a distinction between a tissue that is biologically compatible with microbial growth and one that normally prevents infection through effective mechanical defenses. (ncbi.nlm.nih.gov)\n\nPrimary pathogens can cause disease in otherwise healthy hosts, whereas opportunistic pathogens cause disease particularly when barriers, immune functions, or resident microbial communities have been disturbed. Opportunism does not necessarily require generalized immunodeficiency: a normally resident organism may become harmful after gaining access to a protected site. Staphylococcus epidermidis, ordinarily a member of the skin microbiota, can cause healthcare-associated infection when protective barriers are bypassed. Conversely, bacteria that transiently enter tissues or blood may be eliminated without disease by intact host defenses. The distinction therefore concerns the organism–host relationship and route of access, not simply membership in an invariably harmless or harmful species. (ncbi.nlm.nih.gov)\n\nAge, underlying disease, and immune suppression modify these relationships. Neonates and older adults may have increased susceptibility, while burns, surgery, and invasive devices can breach protective surfaces. In HIV infection, depletion of CD4-positive T cells compromises defenses against particular opportunistic agents. Resident microbial communities provide another layer of protection. Antibiotics can reduce the abundance and diversity of helpful intestinal bacteria, allowing Clostridioides difficile to proliferate. The US Centers for Disease Control and Prevention reports that the likelihood of C. difficile infection can be up to ten times higher during antibiotic treatment and the following month; age 65 or older and immune suppression are additional recognized risk factors. These factors alter susceptibility without making disease inevitable. (ncbi.nlm.nih.gov)\n\nIn plants, the disease triangle represents the interaction of a susceptible host, a compatible disease-causing agent, and an environment conducive to disease development. Susceptibility can vary between cultivars and with tissue age, while environmental moisture and temperature affect the opportunity for infection. Apple scab, caused by Venturia inaequalis, provides a quantitative example: the Mills-table formulation presented by the American Phytopathological Society associates light infection at approximately 18°C with nine hours of leaf wetness. Maturing apple tissues are relatively more resistant than young tissues. Infectious plant disease must nevertheless be distinguished from abiotic injury caused by unsuitable nutrition or environmental stress: such injury does not require an infectious agent, although it can coexist with pathogen-caused disease. (apsnet.org)" }, { "heading": "Mechanisms of Infection and Host Damage", "text": "Infection often begins with attachment to a host surface. Bacterial adhesins—surface proteins, including those carried on pili—bind particular molecules on epithelial cells, helping organisms resist removal by mucus or fluid flow. Attachment does not necessarily entail invasion: some pathogens establish themselves on mucosal surfaces, whereas others enter epithelial cells or cross damaged barriers. An infection remains localized when multiplication is restricted to the initial site; dissemination involves spread into additional tissues, sometimes through blood or lymph. The location of the organism and that of its effects need not coincide, because secreted toxins can act beyond the colonized site. (ncbi.nlm.nih.gov)\n\nExtracellular pathogens multiply on surfaces or in tissue fluids, while intracellular pathogens exploit resources within host cells. These intracellular niches differ: Listeria monocytogenes, for example, grows in the cytoplasm and induces host actin assembly to propel itself. Nutrient acquisition also involves competition with the host. Iron is largely bound to proteins such as transferrin, lactoferrin, and hemoglobin rather than freely available. Many bacteria produce siderophores, small iron-binding molecules whose iron-loaded forms are recognized by uptake receptors; others obtain iron through receptors for host iron-containing compounds. Such systems support multiplication under iron-limited conditions. (ncbi.nlm.nih.gov)\n\nDirect injury includes biochemical disruption as well as cell destruction. Diphtheria toxin enters susceptible cells and ADP-ribosylates elongation factor 2, blocking protein synthesis; its receptor-binding and membrane-translocation regions deliver the catalytic region into the cytosol. Cholera toxin instead alters signaling: modification of the stimulatory G protein increases adenylate cyclase activity and intracellular cyclic AMP, producing intestinal fluid secretion. Thus, severe cholera does not require widespread destruction of intestinal cells. Other bacterial products damage membranes or degrade tissue components, allowing injury and invasion to reinforce one another. These mechanisms distinguish toxin-mediated dysfunction from damage caused simply by microbial growth. (ncbi.nlm.nih.gov)\n\nHost-mediated immunopathology occurs when responses directed against infection also injure host tissue. Bacterial lipopolysaccharide, for example, triggers inflammation and systemic physiological changes rather than acting solely as a cell-killing poison. In tuberculosis, inflammatory responses to the organism contribute substantially to tissue damage, illustrating why disease severity cannot be inferred from bacterial toxin production alone. Pathogen-mediated and host-mediated injury are therefore mechanistically distinguishable but can coexist: microbial components initiate a response whose mediators then account for part of the resulting damage. (ncbi.nlm.nih.gov)\n\nIn plants, entry may require penetration of a cuticle and cell wall. Specialized fungal attachment structures, called appressoria, provide an interface for penetration. In a 2007 study, Ulrike Steiner and Erich-Christian Oerke found that appressoria of the apple-scab fungus Venturia inaequalis lacking a localized melanized ring failed to infect plants. Once established, biotrophic pathogens obtain nutrients from living tissue; necrotrophic pathogens exploit tissue they kill, while hemibiotrophic infections combine an initial living-tissue phase with later destructive growth. These categories describe nutritional strategies and infection phases rather than universally rigid divisions among organisms. (apsjournals.apsnet.org)\n\nPathogen effectors modify plant-cell processes rather than merely digesting tissue. A concrete example is the TAL effector PthXo1 of Xanthomonas oryzae pv. oryzae, which promotes bacterial blight by activating a rice susceptibility gene. In 2006, Bing Yang and colleagues reported that Os8N3 expression was 103-fold higher after inoculation with strain PXO99ᴬ than with its pthXo1-deficient derivative; silencing the plant gene reduced susceptibility to that strain. Subsequent experiments demonstrated direct binding and activation of susceptibility-gene promoters by specific TAL effectors. The pathogen thereby redirects host gene expression, making altered host physiology an integral part of infection. (pmc.ncbi.nlm.nih.gov)" }, { "heading": "Host Defenses, Immune Evasion, and Persistence", "text": "In animals, skin and mucosal epithelia restrict pathogen entry through closely joined cells, antimicrobial secretions, and mechanical removal by mucus and cilia. After these barriers are breached, innate immunity recognizes conserved microbial structures through pattern-recognition receptors. Recognition stimulates cytokines that recruit and activate defensive cells. Neutrophils and macrophages engulf microbes by phagocytosis, enclosing them in phagosomes that normally mature and fuse with lysosomes; acidification, degradative enzymes, and reactive molecules contribute to killing. The complement system deposits proteins on microbial surfaces, facilitating uptake, while terminal complement components can disrupt susceptible microbial membranes. Interferons induce antiviral defenses in infected and neighboring cells. (ncbi.nlm.nih.gov)\n\nIn vertebrates, adaptive immunity adds antigen-specific recognition. Activated B cells produce antibodies that neutralize extracellular viruses and toxins or coat microbes for uptake by phagocytes. Antibodies can also activate complement. T cells recognize pathogen-derived peptides displayed by host major histocompatibility complex molecules: CD8 T cells can kill infected cells, whereas CD4 T cells coordinate responses, help B cells, and activate macrophages. These mechanisms complement rather than replace innate defenses. Immunological memory supports faster responses to subsequent encounters, but protection depends partly on whether the pathogen retains the antigens recognized during the earlier response. (ncbi.nlm.nih.gov)\n\nPathogens evade recognition or resist the mechanisms that follow it. The polysaccharide capsule of Streptococcus pneumoniae impedes effective phagocytosis, although capsule-specific antibodies can promote clearance. Antigenic variation changes the targets recognized by existing antibodies: African trypanosomes switch expression of their variant surface glycoprotein coat, allowing antigenically different parasites to survive as the dominant population is eliminated. Intracellular pathogens instead exploit protected cellular compartments. Mycobacterium tuberculosis, which causes tuberculosis, interferes with phagosome maturation and lysosomal fusion in macrophages; Listeria monocytogenes escapes into the cytoplasm and uses host actin to spread directly between cells, reducing exposure to extracellular antibodies. (ncbi.nlm.nih.gov)\n\nImmune evasion can also alter communication and antigen presentation rather than simply conceal a microbial surface. Some herpesviruses and poxviruses encode proteins that interfere with cytokine activity, complement, or the assembly and display of major histocompatibility complex class I molecules. Such interference can reduce recruitment of defensive cells or recognition by cytotoxic T cells. Intracellular residence alone therefore does not guarantee persistence: infected cells may still display microbial peptides and become targets of cellular immunity. (ncbi.nlm.nih.gov)\n\nAcute infection has a relatively limited course, whereas persistent infection retains the agent over prolonged periods, sometimes with continuing replication and sometimes with intermittent activity. Viral latency is a form of persistence in which the genome remains within host cells while productive replication is largely suppressed. Herpes simplex virus establishes latency in sensory neurons, retaining its DNA in neuronal nuclei with restricted gene expression. Reactivation restores productive replication and can cause recurrent epithelial infection. Varicella-zoster virus likewise persists in sensory ganglia after chickenpox and can later reactivate as shingles, particularly when cellular immune control declines. Absence of symptoms consequently does not necessarily indicate elimination of the agent. (ncbi.nlm.nih.gov)\n\nBiofilms provide another basis for persistence: microorganisms form structured communities embedded in an extracellular polymeric matrix on tissues or surfaces such as catheters and prosthetic devices. Matrix-associated protection and altered growth states can reduce antimicrobial killing without requiring inherited antibiotic resistance. In a 2001 study, Amy L. Spoering and Kim Lewis found that stationary-phase, free-living Pseudomonas aeruginosa survived several antimicrobial challenges at least as well as biofilm populations, implicating physiological state and surviving “persister” subpopulations rather than surface attachment alone. Such tolerance is distinct from a heritable capacity to grow at higher drug concentrations; biofilm organisms may nevertheless possess both properties. (wwwnc.cdc.gov)" }, { "heading": "Reservoirs, Transmission, and Infection Cycles", "text": "A reservoir is the human population, animal population, or environmental habitat in which an infectious agent normally persists and, where biologically applicable, multiplies. The immediate source of exposure need not be the reservoir: contaminated food may deliver an agent maintained in humans or animals. In the chain of infection, an agent leaves through a portal of exit, travels by a transmission route, and reaches a susceptible host through a compatible portal of entry. Exits include respiratory secretions, feces, and blood; entries include respiratory and intestinal mucosa or breaks in the skin. Susceptibility depends on factors including immunity and barrier integrity. Thus, exposure alone does not ensure infection. (archive.cdc.gov)\n\nContact transmission involves direct transfer between hosts or indirect transfer through contaminated hands and objects. Respiratory transmission involves infectious particles expelled during breathing, speaking, coughing, or sneezing; infection may follow inhalation or deposition on susceptible mucous membranes. Particle behavior, ventilation, proximity, and the agent’s biological properties influence transmission, rather than a universal distance boundary. Measles illustrates airborne transmission. In fecal–oral transmission, agents shed in feces reach another host’s mouth through hands, food, or water; norovirus provides a representative example. These routes can overlap: a contaminated surface may connect fecal shedding to oral entry. (cdc.gov)\n\nBloodborne transmission requires infectious blood to reach receptive tissue, for example through a contaminated needle or a sharps injury. Sexual transmission involves exposure during sexual contact, whereas vertical transmission passes an agent from a pregnant or birthing parent to offspring. A single pathogen may use several routes: hepatitis B virus spreads through percutaneous or mucosal exposure to infectious blood and body fluids, through sexual contact, and from mother to infant at birth. It is not ordinarily transmitted through hugging, coughing, shared eating utensils, or casual contact. Route specificity therefore distinguishes infectiousness from general contagiousness in everyday encounters. (cdc.gov)\n\nA vector is a living organism that transfers an infectious agent between hosts. Mechanical carriage, such as transfer of contamination by flies, does not require development or multiplication of the agent within the carrier; biological transmission does. Host categories describe different roles: a definitive host supports sexual reproduction of a parasite, while an intermediate host supports other developmental or asexual stages. In malaria, female Anopheles mosquitoes are both biological vectors and definitive hosts. They ingest Plasmodium gametocytes in blood; sexual development produces stages that ultimately reach the salivary glands and enter another human during feeding. Humans are intermediate hosts, supporting multiplication in liver cells and red blood cells. (archive.cdc.gov)\n\nEnvironmental persistence can bridge the interval between shedding and exposure. Water, food, and contaminated objects may function as temporary vehicles, without constituting habitats that maintain the pathogen independently. Conversely, some environmental sites are genuine reservoirs. Clostridium tetani spores occur in soil and can enter through wounds, where suitable conditions permit germination; tetanus is not transmitted from person to person. This contrasts with contamination of a utensil or meal by an infected handler, in which the object or food serves principally as a vehicle. The distinction concerns the agent’s ecological maintenance, not simply whether it can be detected on a surface. (archive.cdc.gov)\n\nCompletion of an infection cycle also depends on dose and timing. The infectious dose is the quantity of an agent capable of establishing infection under specified host and exposure conditions, not an invariant threshold: ingestion of only 10–100 Shigella organisms can cause disease. The incubation period measures time from infection to symptom onset, not the duration of infectiousness. Asymptomatic carriers and people still incubating disease may shed agents. Norovirus symptoms usually begin 12–48 hours after exposure, but transmission can remain possible for two weeks or more after recovery. Nevertheless, prolonged detection of viral material does not by itself establish equally prolonged infectiousness, because detectable material need not represent viable infectious particles. (wwwnc.cdc.gov)" }, { "heading": "Evolution, Emergence, and Ecological Effects", "text": "Pathogen variation arises through mutation, which changes nucleotide sequences, and genetic recombination, which rearranges existing variation. Natural selection changes the frequency of heritable variants according to their reproductive and transmission success in particular environments; it does not generate changes in anticipation of a pathogen’s needs. In bacteria, horizontal gene transfer also introduces genes from other lineages through uptake of extracellular DNA, bacteriophage-mediated transfer, or conjugation. Conjugative plasmids can carry transferable genetic material, while pathogenicity islands contain clusters of virulence-associated genes, sometimes encoding several functions required for infection. Gene acquisition and gene loss can both contribute to specialization: acquiring an infection-associated gene cluster does not by itself determine disease severity in every host. (ncbi.nlm.nih.gov)\n\nViruses also exchange genetic material, although the mechanisms depend on genome organization. Recombination can produce a sequence assembled from different parental templates; reassortment instead exchanges whole genome segments when compatible segmented viruses infect the same cell. The influenza A(H1N1) virus responsible for the 2009 pandemic carried segments derived from several influenza lineages circulating in pigs, with earlier ancestry in avian and human viruses. Its emergence illustrates how genetic exchange and cross-species transmission can combine, rather than representing the accumulation of point mutations alone. (archive.cdc.gov)\n\nCross-species spillover occurs when an agent passes from a source species and establishes infection in a different host species. Exposure, entry, replication, and onward transmission impose distinct barriers. An isolated infection—or repeated infections continually seeded from an animal reservoir—does not demonstrate self-sustaining transmission in the recipient population. Sustained emergence requires successful transmission between members of that population without continual reintroduction. The distinction is evident in influenza: sporadic human infections with swine-associated variant viruses contrast with the sustained human transmission achieved by the 2009 pandemic virus. Spillover therefore concerns both ecological opportunity and biological compatibility, whereas establishment additionally depends on transmission within the new host population. (journals.plos.org)\n\nChanges in land use and animal husbandry alter contact among wildlife, livestock, and people, while travel and trade transport infected hosts and vectors between regions. During the 1998–1999 Malaysian Nipah outbreak, pigs were an important source of human exposure; Singapore subsequently experienced an outbreak associated with imported infected pigs. Such movements can connect otherwise separated infection systems. Climate change can alter vector distributions and seasonal activity: temperature, rainfall, and humidity influence mosquito development, reproduction, and survival. These effects are geographically contingent rather than uniformly increasing transmission, because suitability also depends on local environmental conditions, host availability, and demographic factors. (who.int)\n\nEcological effects extend beyond mortality in individual hosts. A 2009 study by Ricardo Holdo and colleagues, using Serengeti observations from 1960–2003, supported a cascade in which removal of rinderpest allowed wildebeest populations to increase; heavier grazing reduced grass fuel and fire extent, permitting tree recovery. Pathogens can therefore influence vegetation through their effects on dominant herbivores. In crops, interacting agents can create disease complexes: maize lethal necrosis, reported in Kenya in September 2011, was associated in eastern Africa with coinfection by maize chlorotic mottle virus and sugarcane mosaic virus. Affected plants can develop extensive necrosis, severe stunting, and death, linking pathogen interactions to crop-production losses. (pmc.ncbi.nlm.nih.gov)\n\nHost–pathogen coevolution involves reciprocal selection, not an inevitable progression toward harmlessness. Following the release of myxoma virus in Australia in 1950, Frank Fenner and colleagues documented replacement of the initially highly lethal virus by less lethal variants whose longer infectious periods favored transmission. Rabbits also evolved resistance. In experiments published in 2017, Peter Kerr and colleagues found that many isolates collected in the 1990s produced profound immune suppression and lethal collapse in susceptible laboratory rabbits. The changing outcome depended on host resistance and viral transmission opportunities; initial attenuation did not mark an irreversible evolutionary endpoint. (thereadgroup.net)" }, { "heading": "Detection, Identification, and Attribution of Disease", "text": "Microscopy, culture, biochemical characterization, and tissue examination provide complementary evidence about candidate pathogens. Stained specimens reveal microbial shape, arrangement, and staining properties; these observations can narrow identification without necessarily resolving a species. Culture demonstrates multiplication under the conditions supplied and produces isolates for further testing, but failure to grow an organism does not exclude infection. Biochemical identification distinguishes isolates through properties such as enzyme activity and utilization of particular substrates. Examination of affected tissues adds anatomical context: organisms located within a lesion, alongside characteristic cellular injury or inflammation, provide different evidence from organisms recovered from a surface normally inhabited by microbes. Specimen selection, collection, and transport therefore influence both detection and interpretation. (ncbi.nlm.nih.gov)\n\nImmunological tests distinguish components of an agent from the host’s response to it. An antigen assay uses antibodies to capture or visualize microbial molecules, often proteins, in a specimen. An antibody assay instead detects host immunoglobulins that recognize microbial antigens. Antibody production takes time, and antibodies can persist after infection; a positive result therefore need not identify the cause of a current illness. Depending on the infection and assay, development of detectable antibodies—seroconversion—or a rising titre between acute and convalescent samples provides stronger evidence of recent infection than a single measurement. Vaccination can also produce antibodies: SARS-CoV-2 antibody results, for example, depend partly on whether the assay targets an antigen represented in the vaccine received. (ncbi.nlm.nih.gov)\n\nNucleic-acid amplification detects selected genetic targets rather than requiring visible organisms or growth. In polymerase chain reaction (PCR), primers specify a target sequence that is copied repeatedly; RNA targets require a reverse-transcription step before amplification. Sequencing determines the order of nucleotides, allowing identification and comparison of organisms at a resolution unavailable from morphology alone. Nevertheless, a genetic signal is not equivalent to a viable or disease-causing agent: residual nucleic acid may remain after infection has resolved. CDC notes that SARS-CoV-2 RNA can remain detectable for up to 90 days after a positive test, including after the transmission risk has passed. Such results require interpretation alongside specimen site, timing, and clinical findings. (ncbi.nlm.nih.gov)\n\nAttribution of disease requires causal inference, not identification alone. Relevant evidence includes a compatible clinical syndrome, exposure preceding illness, preferential detection in affected tissues, and greater frequency or abundance of the agent in cases than in appropriate comparison groups. Experimental reproduction of relevant disease features can strengthen attribution where suitable models exist. In 1996, David N. Fredricks and David A. Relman proposed seven sequence-based guidelines for microbial disease causation. These included preferential association of microbial sequences with disease, localization to pathological sites, and changes in sequence abundance with disease resolution or relapse. Their framework emphasized agreement among independent observations rather than treating a positive molecular test as sufficient proof. (pmc.ncbi.nlm.nih.gov)\n\nGenomic epidemiology combines sequence comparisons with dates, locations, exposures, and other contextual information to investigate relationships among infections. Genetic similarity can identify candidate clusters, but epidemiological investigation establishes whether a plausible shared source or transmission relationship exists. During the 2015 investigation of listeriosis linked to Blue Bell ice cream, whole-genome sequencing connected patient isolates with isolates from products and production facilities. On April 8, 2015, CDC reported that isolates from three Texas patients were nearly identical to strains recovered from ice cream produced at the company’s Oklahoma facility. Retrospective comparisons also linked infections from earlier years to contaminated products, showing how archived isolates and exposure information can reveal an outbreak extending beyond its initial recognition. (wwwnc.cdc.gov)" }, { "heading": "Prevention, Control, and Antimicrobial Resistance", "text": "Prevention targets three biological processes: exposure to an agent, transmission between hosts, and establishment of infection in a susceptible host. Safe water, sewage treatment, and food hygiene reduce opportunities for exposure; healthcare infection control interrupts transfer through hands, equipment, and contaminated surroundings. The US Centers for Disease Control and Prevention distinguishes Standard Precautions, applied to all patient care, from additional Transmission-Based Precautions for particular routes of spread. Vector control acts on transmitting organisms rather than necessarily eliminating the pathogen: insecticide-treated nets and indoor residual spraying, for example, target mosquitoes involved in malaria transmission. Vaccination increases host protection by inducing antigen-specific responses and immunological memory, enabling faster responses to subsequent exposure. These measures act at different points and can be combined. (cdc.gov)\n\nAntimicrobial medicines differ according to the biological machinery they affect. Antibacterial agents can inhibit bacterial cell-wall synthesis, protein synthesis, or nucleic-acid metabolism; beta-lactams, for example, interfere with construction of the peptidoglycan wall. Antiviral drugs instead interfere with stages of viral replication, including genome copying or processing of viral proteins. Antifungals exploit fungal features such as membrane sterols: amphotericin B interacts with ergosterol and disrupts membrane integrity. Antiparasitic medicines act against protozoa or helminths, with activity depending on the organism and sometimes its developmental stage. “Antimicrobial” therefore does not mean universally active against pathogens: antibacterial drugs do not treat viral infections, and activity against one fungal or parasitic species does not establish activity against another. (ncbi.nlm.nih.gov)\n\nAntimicrobial resistance concerns properties of the infectious agent, not a patient becoming “resistant” to medicine. Heritable variation arises through mutation or acquisition of genetic material; drug exposure then favors organisms able to survive and reproduce under that exposure. In bacteria, horizontal gene transfer can distribute resistance determinants between lineages, including through plasmids. Mechanisms include drug-inactivating enzymes, alteration of the drug’s target, reduced entry, and active export. Beta-lactamases, for example, break down susceptible beta-lactam antibiotics. Resistant organisms can also spread to hosts who have never received the selecting medicine. Misuse and overuse accelerate selection, while infection prevention and antimicrobial stewardship address, respectively, transmission and avoidable selective pressure. WHO estimated that bacterial resistance directly caused 1.27 million deaths worldwide in 2019 and was associated with 4.95 million; the larger figure includes deaths involving resistant infections that were not necessarily attributable to resistance itself. (cdc.gov)\n\nPlant-disease management similarly combines host protection, exclusion, and interruption of infection cycles. Resistant cultivars may reduce infection, pathogen development, or production of new inoculum. Quarantine and pathogen-free planting material limit introductions through traded plants, seeds, and associated material. Rotation to nonsusceptible crops removes suitable hosts for particular pathogens, while removal of infected plants or residues reduces inoculum available for later infections. These measures depend on pathogen biology: an intervention that reduces initial inoculum differs from one that slows repeated infection during a growing season. The American Phytopathological Society accordingly describes management in terms of reducing epidemic development rather than assuming that complete pathogen elimination is generally achievable. Its scope includes agricultural crops as well as diseases affecting trees and other plants. (apsnet.org)\n\nCoordinated surveillance connects laboratory findings with disease occurrence and antimicrobial use. WHO launched its Global Antimicrobial Resistance Surveillance System, subsequently expanded to include use, in October 2015 to support standardized reporting across countries. National public-health agencies investigate outbreaks and operate or coordinate laboratory networks, while international organizations aggregate information and support comparable methods. The One Health framework extends coordination across human, animal, plant, and environmental sectors. In October 2022, WHO, the Food and Agriculture Organization, the World Organisation for Animal Health, and the United Nations Environment Programme published their Joint Plan of Action for 2022–2026, explicitly organizing collaboration across these interfaces, including work on antimicrobial resistance. (emro.who.int)" } ], "links": [ "infectious-disease", "bacteria", "virus", "fungi", "medicine", "public-health", "ecology", "epidemiology", "disease", "taxonomy", "microorganism", "prokaryote", "tuberculosis", "escherichia-coli", "dna", "rna", "eukaryote", "malaria", "germ-theory-of-disease", "louis-pasteur", "causal-inference", "gene", "temperature", "immunodeficiency", "hiv-aids", "t-cell", "protein", "cell", "cholera", "inflammation", "cell-wall", "gene-expression", "innate-immunity", "cytokine", "neutrophil", "macrophage", "phagocytosis", "complement-system", "interferon", "adaptive-immunity", "b-cell", "antibody", "immunological-memory", "antibiotic-resistance", "measles", "hepatitis-b", "incubation-period", "mutation", "natural-selection", "horizontal-gene-transfer", "plasmid", "influenza", "trade", "climate-change", "microscope", "antigen", "polymerase-chain-reaction", "dna-sequencing", "vaccine", "antiviral-drug", "public-health-surveillance" ], "sources": [ { "title": "Introduction to Pathogens - Molecular Biology of the Cell - NCBI Bookshelf", "url": "https://www.ncbi.nlm.nih.gov/books/NBK26917/" }, { "title": "About Staph Food Poisoning | Staph Food Poisoning | CDC", "url": "https://www.cdc.gov/staph-food-poisoning/about/" }, { "title": "Bacterial Pathogenesis - Medical Microbiology - NCBI Bookshelf", "url": "https://www.ncbi.nlm.nih.gov/books/NBK8526/?report=classic" }, { "title": "Epidemiology Glossary | Reproductive Health | CDC", "url": "https://www.cdc.gov/reproductive-health/glossary/" }, { "title": "Epidemiology Glossary | Reproductive Health | CDC", "url": "https://www.cdc.gov/reproductive-health/glossary/index.html" }, { "title": "Clinical Overview of Tuberculosis", "url": "https://www.cdc.gov/tb/hcp/clinical-overview/" }, { "title": "About Escherichia coli Infection", "url": "https://www.cdc.gov/ecoli/about/" }, { "title": "Recommendations for Diagnosis of Shiga Toxin–Producing Escherichia coli Infections by Clinical Laboratories", "url": "https://www.cdc.gov/MMWR/Preview/MMWRhtml/rr5812a1.htm" }, { "title": "Structure and Classification of Viruses", "url": "https://www.ncbi.nlm.nih.gov/books/NBK8174/?report=reader" }, { "title": "About Parasites", "url": "https://www.cdc.gov/parasites/about/" }, { "title": "Susceptibility of Human Prion Protein to Conversion by Chronic Wasting Disease Prions", "url": "https://wwwnc.cdc.gov/eid/article/24/8/16-1888_article" }, { "title": "The middle years 1862-1877", "url": "https://www.pasteur.fr/en/about-us/middle-years-1862-1877" }, { "title": "Robert Koch", "url": "https://www.rki.de/EN/Institute/The-RKI/History/Robert-Koch/robert-koch-node.html" }, { "title": "Tuberculosis: Read More", "url": "https://educationalgames.nobelprize.org/educational/medicine/tuberculosis/readmore.html" }, { "title": "FAQ: Human Microbiome", "url": "https://www.ncbi.nlm.nih.gov/books/NBK562894/" }, { "title": "Free Executive Summary", "url": "https://www.ncbi.nlm.nih.gov/books/n/nap11026/pdf/" }, { "title": "Sequence-Based Identification of Microbial Pathogens: a Reconsideration of Koch’s Postulates", "url": "https://cmgm-new.stanford.edu/micro/MI209/postulates.pdf" }, { "title": "Molecular Koch's postulates applied to microbial pathogenicity", "url": "https://pubmed.ncbi.nlm.nih.gov/3055197/" }, { "title": "Novel proteinaceous infectious particles cause scrapie", "url": "https://pubmed.ncbi.nlm.nih.gov/6801762/" }, { "title": "A brief history of prions", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC4626585/" }, { "title": "The Nobel Prize in Physiology or Medicine 1997", "url": "https://www.nobelprize.org/prizes/medicine/1997/summary/-/" }, { "title": "Cellular receptor for poliovirus: molecular cloning, nucleotide sequence, and expression of a new member of the immunoglobulin superfamily", "url": "https://pubmed.ncbi.nlm.nih.gov/2538245/" }, { "title": "Bacterial Pathogenesis - Medical Microbiology", "url": "https://www.ncbi.nlm.nih.gov/books/NBK8526/?report=printable" }, { "title": "Chapter 9 Infection - Nursing Fundamentals", "url": "https://www.ncbi.nlm.nih.gov/books/NBK591816/" }, { "title": "Chapter 41. Preventing Health Care–Associated Infections", "url": "https://www.ncbi.nlm.nih.gov/books/NBK2683/pdf/ch41.pdf" }, { "title": "About C. diff", "url": "https://www.cdc.gov/c-diff/about/" }, { "title": "Corynebacterium Diphtheriae — Medical Microbiology", "url": "https://www.ncbi.nlm.nih.gov/books/NBK7971/" }, { "title": "Pathogens, Infection, and Innate Immunity — Molecular Biology of the Cell", "url": "https://www.ncbi.nlm.nih.gov/books/NBK21072/" }, { "title": "The nature and action of cholera toxin", "url": "https://pubmed.ncbi.nlm.nih.gov/791600/" }, { "title": "Os8N3 is a host disease-susceptibility gene for bacterial blight of rice", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC1502487/" }, { "title": "Promoter elements of rice susceptibility genes are bound and activated by specific TAL effectors from the bacterial blight pathogen, Xanthomonas oryzae pv. oryzae", "url": "https://pubmed.ncbi.nlm.nih.gov/20345643/" }, { "title": "Innate Immunity - Molecular Biology of the Cell", "url": "https://www.ncbi.nlm.nih.gov/books/NBK26846/" }, { "title": "Pathogens have evolved various means of evading or subverting normal host defenses - Immunobiology", "url": "https://www.ncbi.nlm.nih.gov/sites/books/NBK27176/" }, { "title": "Molecular basis of HSV latency and reactivation - Human Herpesviruses", "url": "https://www.ncbi.nlm.nih.gov/books/NBK47421/" }, { "title": "Biofilms and Device-Associated Infections", "url": "https://wwwnc.cdc.gov/eid/article/7/2/70-0277_article" }, { "title": "Biofilms and planktonic cells of Pseudomonas aeruginosa have similar resistance to killing by antimicrobials", "url": "https://pubmed.ncbi.nlm.nih.gov/11698361/" }, { "title": "Principles of Epidemiology: Lesson 1, Section 10—Chain of Infection", "url": "https://archive.cdc.gov/www_cdc_gov/csels/dsepd/ss1978/lesson1/section10.html" }, { "title": "Review of Scientific Data Regarding Transmission of Infectious Agents in Healthcare Settings", "url": "https://www.cdc.gov/infection-control/hcp/isolation-precautions/scientific-review.html" }, { "title": "About Norovirus", "url": "https://www.cdc.gov/norovirus/about/index.html" }, { "title": "Prevention of Hepatitis B Virus Infection in the United States: Recommendations of the Advisory Committee on Immunization Practices", "url": "https://www.cdc.gov/mmwr/volumes/67/rr/rr6701a1.htm" }, { "title": "Hepatitis B & Sexual Health", "url": "https://www.cdc.gov/hepatitis-b/media/HepBSexualHealth.pdf" }, { "title": "Viral Hepatitis—STI Treatment Guidelines", "url": "https://www.cdc.gov/std/treatment-guidelines/hbv.htm" }, { "title": "CDC DPDx—Malaria", "url": "https://www.cdc.gov/dpdx/malaria/index.html" }, { "title": "Changing Patterns of Autochthonous Malaria Transmission in the United States: A Review of Recent Outbreaks", "url": "https://wwwnc.cdc.gov/eid/article/2/1/96-0104_article" }, { "title": "Chapter 16: Tetanus—Manual for the Surveillance of Vaccine-Preventable Diseases", "url": "https://www.cdc.gov/surv-manual/php/table-of-contents/chapter-16-tetanus.html" }, { "title": "Chapter 21: Tetanus—Pink Book", "url": "https://www.cdc.gov/pinkbook/hcp/table-of-contents/chapter-21-tetanus.html" }, { "title": "Shigella Bacteremia, Georgia, USA, 2002–2012", "url": "https://wwwnc.cdc.gov/eid/article/26/1/18-1698_article" }, { "title": "Updated Norovirus Outbreak Management and Disease Prevention Guidelines", "url": "https://www.cdc.gov/mmwr/pdf/rr/rr6003.pdf" }, { "title": "Genetics — Medical Microbiology", "url": "https://www.ncbi.nlm.nih.gov/books/NBK7908/" }, { "title": "Challenges of Predicting Pathogenicity from Sequence", "url": "https://www.ncbi.nlm.nih.gov/books/NBK50869/" }, { "title": "Pathogen Evolution — Microbial Evolution and Co-Adaptation", "url": "https://ncbi.nlm.nih.gov/sites/books/NBK45713/?report=reader" }, { "title": "CDC H1N1 Flu: Origin of 2009 H1N1 Flu (Swine Flu)", "url": "https://archive.cdc.gov/www_cdc_gov/h1n1flu/information_h1n1_virus_qa.htm" }, { "title": "How Flu Viruses Can Change: “Drift” and “Shift”", "url": "https://www.cdc.gov/flu/php/viruses/change.html?CDC_AAref_Val=%3Cbr%3Ehttps%3A%2F%2Fwww.cdc.gov%2Fflu%2Fabout%2Fviruses%2Fchange.htm" }, { "title": "Pathogen host jump risk is not predicted by spillover rate, but rather by novelty", "url": "https://journals.plos.org/plosbiology/article?id=10.1371%2Fjournal.pbio.3003640" }, { "title": "Key Facts about Human Infections with Variant Viruses", "url": "https://archive.cdc.gov/www_cdc_gov/flu/swineflu/keyfacts-variant.htm" }, { "title": "The 2009 H1N1 Pandemic: Summary Highlights, April 2009–April 2010", "url": "https://archive.cdc.gov/www_cdc_gov/h1n1flu/cdcresponse.htm" }, { "title": "New report highlights the impact of changes in environment on One Health", "url": "https://www.who.int/europe/news/item/01-07-2022-new-report-highlights-the-impact-of-changes-in-environment-on-one-health" }, { "title": "Nipah virus", "url": "https://www.who.int/news-room/fact-sheets/detail/nipah-virus" }, { "title": "Vector-borne diseases", "url": "https://www.who.int/en/news-room/fact-sheets/detail/vector-borne-diseases" }, { "title": "El Niño Southern Oscillation (ENSO)", "url": "https://www.who.int/news-room/fact-sheets/detail/el-nino-southern-oscillation-%28enso%29" }, { "title": "Principles of Diagnosis - Medical Microbiology", "url": "https://www.ncbi.nlm.nih.gov/books/NBK8014/?report=classic" }, { "title": "Appropriate use of the microbiology laboratory in the diagnosis of infectious diseases.", "url": "https://pubmed.ncbi.nlm.nih.gov/3314605/" }, { "title": "Interim Guidelines for COVID-19 Antibody Testing", "url": "https://archive.cdc.gov/www_cdc_gov/coronavirus/2019-ncov/hcp/testing/antibody-tests-guidelines.html" }, { "title": "What is Advanced Molecular Detection (AMD)?", "url": "https://www.cdc.gov/advanced-molecular-detection/about/index.html" }, { "title": "Overview of Testing for SARS-CoV-2", "url": "https://www.cdc.gov/covid/hcp/clinical-care/overview-testing-sars-cov-2.html" }, { "title": "Sequence-based identification of microbial pathogens: a reconsideration of Koch's postulates", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC172879/" }, { "title": "Sequence-based identification of microbial pathogens: a reconsideration of Koch's postulates", "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC172879/pdf/090018.pdf" }, { "title": "Strategies and Opportunities to Improve Community Health through Advanced Molecular Detection and Genomic Surveillance of Infectious Diseases", "url": "https://wwwnc.cdc.gov/eid/article/31/13/24-1408_article" }, { "title": "Multistate Outbreak of Listeriosis Linked to Blue Bell Creameries Products", "url": "https://archive.cdc.gov/www_cdc_gov/listeria/outbreaks/ice-cream-03-15/index.html" }, { "title": "III. Precautions to Prevent Transmission of Infectious Agents", "url": "https://www.cdc.gov/infection-control/hcp/isolation-precautions/precautions.html" }, { "title": "Standard Precautions for All Patient Care", "url": "https://www.cdc.gov/infection-control/hcp/basics/standard-precautions.html" }, { "title": "Global Malaria Programme: Vector control", "url": "https://www.who.int/teams/global-malaria-programme/prevention/vector-control/" }, { "title": "Vaccines and immunization: What is vaccination?", "url": "https://www.who.int/news-room/questions-and-answers/item/vaccines-and-immunization-what-is-vaccination?topicsurvey=ht7j2q%29" }, { "title": "Antimicrobial Chemotherapy", "url": "https://ncbi.nlm.nih.gov/books/NBK7986/" }, { "title": "Antifungal Agents", "url": "https://www.ncbi.nlm.nih.gov/books/NBK8263/" }, { "title": "Antimicrobial resistance", "url": "https://www.who.int/news-room/fact-sheets/detail/antimicrobial-resistance" }, { "title": "About Antimicrobial Resistance", "url": "https://www.cdc.gov/antimicrobial-resistance/about/" }, { "title": "Antimicrobial Resistance: Causes and How It Spreads", "url": "https://www.cdc.gov/antimicrobial-resistance/causes/" }, { "title": "Antibiotic Resistance Threats in the United States 2019", "url": "https://stacks.cdc.gov/view/cdc/82532/cdc_82532_DS1.pdf" } ], "license": "https://creativecommons.org/licenses/by/4.0/" }