biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...

, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

or agent that can produce

disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...

. A pathogen may also be referred to as an infectious agent, or simply a

germ Germ or germs may refer to: Science * Germ (microorganism), an informal word for a pathogen * Germ cell, cell that gives rise to the gametes of an organism that reproduces sexually * Germ layer, a primary layer of cells that forms during embryo ...

. The term ''pathogen'' came into use in the 1880s. Typically, the term ''pathogen'' is used to describe an ''infectious'' microorganism or agent, such as a

virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...

, bacterium, protozoan, prion,

viroid Viroids are small single-stranded, circular RNAs that are infectious pathogens. Unlike viruses, they have no protein coating. All known viroids are inhabitants of angiosperms (flowering plants), and most cause diseases, whose respective economi ...

, or fungus. Small animals, such as helminths and insects, can also cause or transmit disease. However, these animals are usually referred to as parasites rather than pathogens. The scientific study of microscopic organisms, including microscopic pathogenic organisms, is called microbiology, while parasitology refers to the scientific study of parasites and the organisms that host them. There are several pathways through which pathogens can invade a host. The principal pathways have different episodic time frames, but

soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...

has the longest or most persistent potential for harboring a pathogen. Diseases in humans that are caused by infectious agents are known as pathogenic diseases. Not all diseases are caused by pathogens, other causes are, for example, toxins, genetic disorders and the host's own immune system.

Pathogenicity

Pathogenicity is the potential disease-causing capacity of pathogens. Pathogenicity is related to virulence in meaning, but some authorities have come to distinguish it as a ''qualitative'' term, whereas the latter is ''quantitative''. By this standard, an organism may be said to be pathogenic or non-pathogenic in a particular context, but not "more pathogenic" than another. Such comparisons are described instead in terms of relative virulence. Pathogenicity is also distinct from the transmissibility of a virus, which quantifies the risk of infection. A pathogen may be described in terms of its ability to produce toxins, enter tissue, colonize, hijack nutrients, and its ability to immunosuppress the host.

Context-dependent pathogenicity

It is common to speak of an entire species of bacteria as pathogenic when it is identified as the cause of a disease ''(cf.

Koch's postulates Koch's postulates ( )"Koch"
''

opportunistic infections in

immunocompromised Immunodeficiency, also known as immunocompromisation, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that a ...

hosts, acquire

virulence factor Virulence factors (preferably known as pathogenicity factors or effectors in plant science) are cellular structures, molecules and regulatory systems that enable microbial pathogens (bacteria, viruses, fungi, and protozoa) to achieve the following ...

s by plasmid infection, become transferred to a different site within the host, or respond to changes in the overall numbers of other bacteria present. For example, infection of mesenteric

lymph glands A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that include ...

of mice with ''

Yersinia ''Yersinia'' is a genus of bacteria in the family Yersiniaceae. ''Yersinia'' species are Gram-negative, coccobacilli bacteria, a few micrometers long and fractions of a micrometer in diameter, and are facultative anaerobes. Some members of ''Yer ...

'' can clear the way for continuing infection of these sites by ''

Lactobacillus ''Lactobacillus'' is a genus of Gram-positive, aerotolerant anaerobes or microaerophilic, rod-shaped, non-spore-forming bacteria. Until 2020, the genus ''Lactobacillus'' comprised over 260 phylogenetically, ecologically, and metabolically div ...

'', possibly by a mechanism of "immunological scarring".

Related concepts

Virulence

Virulence (the tendency of a pathogen to reduce a host's fitness) evolves when a pathogen can spread from a diseased host, despite the host becoming debilitated. Horizontal transmission occurs between hosts of the same species, in contrast to vertical transmission, which tends to evolve toward symbiosis (after a period of high morbidity and mortality in the population) by linking the pathogen's evolutionary success to the evolutionary success of the host organism.

Evolutionary biology Evolutionary biology is the subfield of biology that studies the evolutionary processes ( natural selection, common descent, speciation) that produced the diversity of life on Earth. It is also defined as the study of the history of life ...

proposes that many pathogens evolve an optimal virulence at which the fitness gained by increased replication rates is balanced by trade-offs in reduced transmission, but the exact mechanisms underlying these relationships remain controversial.

Transmission

Transmission of pathogens occurs through many different routes, including airborne, direct or indirect contact, sexual contact, through blood, breast milk, or other body fluids, and through the fecal-oral route.

Types of pathogens

Algae

Algae are single-celled eukaryotes that are generally non-pathogenic although pathogenic varieties do exist. ''

Protothecosis Protothecosis, otherwise known as Algaemia, is a disease found in dogs, cats, cattle, and humans caused by a type of green alga known as ''Prototheca'' that lacks chlorophyll and enters the human or animal bloodstream. It and its close relative ' ...

'' is a disease found in dogs, cats, cattle, and humans caused by a type of green alga known as

prototheca ''Prototheca'' is a genus of algae in the family Chlorellaceae. All the species within this genus, even though classified as green algae, have forfeited their photosynthetic ability and have switched to parasitism. Some species can cause the dise ...

that lacks chlorophyll. Often found in soil and sewage, the species '' Prototheca wickerhami'' is the cause for most human cases of the rare infection of protothecosis.

Bacteria

The vast majority of bacteria, which can range between 0.15 and 700 μM in length, are harmless or beneficial to humans. However, a relatively small list of pathogenic bacteria can cause infectious diseases. Pathogenic bacteria have several ways that they can cause disease. They can either directly affect the cells of their host, produce endotoxins that damage the cells of their host, or cause a strong enough immune response that the host cells are damaged. Shigella stool

One of the bacterial diseases with the highest disease burden is tuberculosis, caused by the bacterium '' Mycobacterium tuberculosis'', which killed 1.5 million people in 2013, mostly in sub-Saharan Africa. Pathogenic bacteria contribute to other globally significant diseases, such as

pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severi ...

, which can be caused by bacteria such as ''

Streptococcus ''Streptococcus'' is a genus of gram-positive ' (plural ) or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occurs ...

'' and ''

Pseudomonas ''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able t ...

'', and

foodborne illness Foodborne illness (also foodborne disease and food poisoning) is any illness resulting from the spoilage of contaminated food by pathogenic bacteria, viruses, or parasites that contaminate food, as well as prions (the agents of mad cow disease ...

es, which can be caused by bacteria such as '' Shigella'', '' Campylobacter'', and '' Salmonella''. In patients with cystic fibrosis, ''Pseudomonas'' bacteria can form a biofilm that has a high resistance to the immune system and antibiotics by developing adaptive mutations and producing virulence factors. Pathogenic bacteria also cause infections such as tetanus,

typhoid fever Typhoid fever, also known as typhoid, is a disease caused by '' Salmonella'' serotype Typhi bacteria. Symptoms vary from mild to severe, and usually begin six to 30 days after exposure. Often there is a gradual onset of a high fever over several ...

, diphtheria, syphilis, and

leprosy Leprosy, also known as Hansen's disease (HD), is a long-term infection by the bacteria ''Mycobacterium leprae'' or ''Mycobacterium lepromatosis''. Infection can lead to damage of the nerves, respiratory tract, skin, and eyes. This nerve damag ...

Fungi

Fungi are eukaryotic organisms that can function as pathogens. There are approximately 300 known fungi that are pathogenic to humans including ''

Candida albicans ''Candida albicans'' is an opportunistic pathogenic yeast that is a common member of the human gut flora. It can also survive outside the human body. It is detected in the gastrointestinal tract and mouth in 40–60% of healthy adults. It is usu ...

'', which is the most common cause of thrush, and '' Cryptococcus neoformans'', which can cause a severe form of meningitis. The typical fungal spore size is <4.7 μm in length, but some spores may be larger.

Prions

Variant Creutzfeldt-Jakob disease (vCJD), H&E

Prions Prions are misfolded proteins that have the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseases in humans and many other animals. It i ...

are misfolded proteins that are transmissible and can influence the abnormal folding of normal proteins in the brain. They do not contain any DNA or RNA and cannot replicate other than to convert already existing normal proteins to the misfolded state. These abnormally folded proteins are found characteristically in many neurodegenerative diseases as they aggregate the central nervous system and create plaques that damages the tissue structure. This essentially creates "holes" in the tissue. It has been found that prions transmit in three ways: obtained, familial, and sporadic. It has also been found that plants play the role of vectors for prions. There are eight different diseases that affect mammals that are caused by prions such as

scrapie Scrapie () is a fatal, degenerative disease affecting the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies (TSEs), and as such it is thought to be caused by a prion. Scrapie has been known since ...

bovine spongiform encephalopathy Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is an incurable and invariably fatal neurodegenerative disease of cattle. Symptoms include abnormal behavior, trouble walking, and weight loss. Later in the course of t ...

(mad cow disease) and feline spongiform encephalopathy (FSE). There are also ten diseases that affect humans, such as

Creutzfeldt–Jakob disease Creutzfeldt–Jakob disease (CJD), also known as subacute spongiform encephalopathy or neurocognitive disorder due to prion disease, is an invariably fatal degenerative brain disorder. Early symptoms include memory problems, behavioral changes ...

(CJD) and

Fatal familial insomnia Fatal insomnia is an extremely rare genetic (and even more rarely, sporadic) disorder that results in trouble sleeping as its hallmark symptom. The problems with sleeping typically start out gradually and worsen over time. Eventually, the patien ...

(FFI).

Viroids

Not to be confused with virusoid or

. Viroids are the smallest infectious pathogens known. They are composed solely of a short strand of circular, single-stranded RNA that has no protein coating. All known viroids are inhabitants of higher plants, and most cause diseases, whose respective economic importance on humans vary widely.

Viruses

Viruses are small particles, typically between 20 and 300 nanometers in length, containing RNA or DNA. Viruses require a host cell to replicate. Some of the diseases that are caused by viral pathogens include

smallpox Smallpox was an infectious disease caused by variola virus (often called smallpox virus) which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) c ...

, influenza, mumps, measles, chickenpox, ebola,

HIV The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...

, rubella, and

COVID-19 Coronavirus disease 2019 (COVID-19) is a contagious disease caused by a virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The first known case was identified in Wuhan, China, in December 2019. The disease quickly ...

. Pathogenic viruses are mainly from the families Adenoviridae,

Coronaviridae ''Coronaviridae'' is a family of enveloped, positive-strand RNA viruses which infect amphibians, birds, and mammals. The group includes the subfamilies '' Letovirinae'' and ''Orthocoronavirinae;'' the members of the latter are known as coronavi ...

Picornaviridae Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are viruses that represent a large family of small, positive-sense, single-stranded RNA viruses with a 30&nbs ...

Herpesviridae ''Herpesviridae'' is a large family of DNA viruses that cause infections and certain diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word ''ἕρπει� ...

, Hepadnaviridae,

Flaviviridae ''Flaviviridae'' is a family of enveloped positive-strand RNA viruses which mainly infect mammals and birds. They are primarily spread through arthropod vectors (mainly ticks and mosquitoes). The family gets its name from the yellow fever viru ...

Retroviridae A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase ...

, Orthomyxoviridae,

Paramyxoviridae ''Paramyxoviridae'' (from Greek ''para-'' “by the side of” and ''myxa'' “mucus”) is a family of negative-strand RNA viruses in the order '' Mononegavirales''. Vertebrates serve as natural hosts. Diseases associated with this family inclu ...

, Papovaviridae,

Polyomavirus ''Polyomaviridae'' is a family of viruses whose natural hosts are primarily mammals and birds. As of 2020, there are six recognized genera and 117 species, five of which are unassigned to a genus. 14 species are known to infect humans, while othe ...

, Rhabdoviridae, and

Togaviridae This category is for articles about virus families (or redirects to such articles). There should be no subcategories. families Families (biology) ...

. HIV is a notable member of the family Retroviridae which affected 37.9 million people across the world in 2018.

Other parasites

Protozoans are single-celled eukaryotes that feed on microorganisms and organic tissues. Considered as "one-celled animal" as they have animal like behaviors such as motility, predation, and a lack of a cell wall. Many protozoan pathogens are considered human parasites as they cause a variety of diseases such as:

malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...

amoebiasis Amoebiasis, or amoebic dysentery, is an infection of the intestines caused by a parasitic amoeba '' Entamoeba histolytica''. Amoebiasis can be present with no, mild, or severe symptoms. Symptoms may include lethargy, loss of weight, colonic ...

, giardiasis,

toxoplasmosis Toxoplasmosis is a parasitic disease caused by '' Toxoplasma gondii'', an apicomplexan. Infections with toxoplasmosis are associated with a variety of neuropsychiatric and behavioral conditions. Occasionally, people may have a few weeks or mont ...

cryptosporidiosis Cryptosporidiosis, sometimes informally called crypto, is a parasitic disease caused by '' Cryptosporidium'', a genus of protozoan parasites in the phylum Apicomplexa. It affects the distal small intestine and can affect the respiratory tra ...

, trichomoniasis, Chagas disease, leishmaniasis, African trypanosomiasis (sleeping sickness), ''Acanthamoeba'' keratitis, and

primary amoebic meningoencephalitis Naegleriasis (also known as primary amoebic meningoencephalitis; PAM) is an almost invariably fatal infection of the brain by the free-living unicellular eukaryote ''Naegleria fowleri''. Symptoms are meningitis-like and include headache, fever, ...

(naegleriasis).

Parasitic worm Parasitic worms, also known as helminths, are large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as sc ...

s (helminths) are macroparasites that can be seen by the naked eye. Worms live and feed in their living host, receiving nourishment and shelter while affecting the host's way of digesting nutrients. They also manipulate the host's immune system by secreting immunomodulatory products which allows them to live in their host for years. Many parasitic worms are more commonly intestinal that are soil-transmitted and infect the digestive tract; other parasitic worms are found in the host's blood vessels. Parasitic worms living in the host can cause weakness and even lead to many diseases. Parasitic worms can cause many diseases to both humans and animals. Helminthiasis (worm infection), ascariasis, and

enterobiasis Pinworm infection (threadworm infection in the UK), also known as enterobiasis, is a human parasitic disease caused by the pinworm. The most common symptom is itching in the anal area. The period of time from swallowing eggs to the appearance ...

(pinworm infection) are a few that are caused by various parasitic worms.

Pathogen hosts

Bacteria

Although bacteria can be pathogens themselves, they can also be infected by pathogens. Bacteriophages are viruses, also known as phage (plural) and phages, that infect bacteria often leading to the death of the bacteria that was infected. Common bacteriophages include T7 and

Lambda Lambda (}, ''lám(b)da'') is the 11th letter of the Greek alphabet, representing the voiced alveolar lateral approximant . In the system of Greek numerals, lambda has a value of 30. Lambda is derived from the Phoenician Lamed . Lambda gave ri ...

phage. There are bacteriophages that infect every kind of bacteria including both gram-negative and

gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bact ...

. Even pathogenic bacteria that infect other species, including humans, can be infected with a phage.

Plants

Plants can play host to a wide range of pathogen types including viruses, bacteria, fungi, nematodes, and even other plants. Notable plant viruses include the

Papaya ringspot virus ''Papaya ringspot virus'' (PRSV) is a pathogenic plant virus in the genus ''Potyvirus'' and the virus family ''Potyviridae'' which primarily infects the papaya tree. The virus is a non-enveloped, flexuous rod-shaped particle that is between 760& ...

which has caused millions of dollars of damage to farmers in Hawaii and Southeast Asia, and the

Tobacco mosaic virus ''Tobacco mosaic virus'' (TMV) is a positive-sense single-stranded RNA virus species in the genus ''Tobamovirus'' that infects a wide range of plants, especially tobacco and other members of the family Solanaceae. The infection causes characteri ...

which caused scientist

Martinus Beijerinck Martinus Willem Beijerinck (, 16 March 1851 – 1 January 1931) was a Dutch microbiologist and botanist who was one of the founders of virology and environmental microbiology. He is credited with the discovery of viruses, which he called "'' ...

to coin the term "virus" in 1898. Bacterial plant pathogens are also a serious problem causing leaf spots, blights, and rots in many plant species. The top two bacterial pathogens for plants are '' Pseudomonas syringae'' and '' Ralstonia solanacearum'' which cause leaf browning and other issues in potatoes, tomatoes, and bananas. Brown Rot on Apple

Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

are another major pathogen type for plants. They can cause a wide variety of issues such as shorter plant height, growths or pits on tree trunks, root or seed rot, and leaf spots. Common and serious plant fungi include the rice blast fungus, Dutch elm disease, chestnut blight and the black knot and brown rot diseases of cherries, plums, and peaches. It is estimated that pathogenic fungi alone cause up to a 65% reduction in crop yield. Overall, plants have a wide array of pathogens and it has been estimated that only 3% of the disease caused by plant pathogens can be managed.

Animals

Animals often get infected with many of the same or similar pathogens as humans including prions, viruses, bacteria, and fungi. While wild animals often get illnesses, the larger danger is for livestock animals. It is estimated that in rural settings, 90% or more of livestock deaths can be attributed to pathogens. The prion disease

, commonly known as Mad cow disease, is one of the few prion diseases that affect animals. Other animal diseases include a variety of immunodeficiency disorders that are caused by viruses related to the Human immunodeficiency virus (HIV) including BIV and FIV.

Humans

Humans can be infected with many types of pathogens including prions, viruses, bacteria, and fungi. Viruses and bacteria that infect humans can cause symptoms such as sneezing, coughing, fever, vomiting, and even lead to death. Some of these symptoms are caused by the virus itself, while others are caused by the immune system of the infected person.

Treatment

Prion

Despite many attempts, to date no therapy has been shown to halt the progression of prion diseases.

Virus

A variety of prevention and treatment options exist for some viral pathogens. Vaccines are one common and effective preventive measure against a variety of viral pathogens. Vaccines prime the immune system of the host, so that when the potential host encounters the virus in the wild, the immune system can defend against infection quickly. Vaccines exist for viruses such as the measles, mumps, and rubella viruses and the influenza virus. Some viruses such as

dengue Dengue fever is a mosquito-borne tropical disease caused by the dengue virus. Symptoms typically begin three to fourteen days after infection. These may include a high fever, headache, vomiting, muscle and joint pains, and a characteristic ...

, and chikungunya do not have vaccines available. Treatment of viral infections often involves treating the symptoms of the infection rather than providing any medication that affects the viral pathogen itself. Treating the symptoms of a viral infection gives the host immune system time to develop antibodies against the viral pathogen which will then clear the infection. In some cases, treatment against the virus is necessary. One example of this is HIV where

antiretroviral therapy The management of HIV/AIDS normally includes the use of multiple antiretroviral drugs as a strategy to control HIV infection. There are several classes of antiretroviral agents that act on different stages of the HIV life-cycle. The use of multi ...

, also known as ART or HAART, is needed to prevent immune cell loss and the progression into AIDS.

Bacteria

Much like viral pathogens, infection by certain bacterial pathogens can be prevented via vaccines. Vaccines against bacterial pathogens include the

anthrax vaccine Anthrax vaccines are vaccines to prevent the livestock and human disease anthrax, caused by the bacterium ''Bacillus anthracis''. They have had a prominent place in the history of medicine, from Pasteur's pioneering 19th-century work with cattle ...

and the

pneumococcal vaccine Pneumococcal vaccines are vaccines against the bacterium '' Streptococcus pneumoniae''. Their use can prevent some cases of pneumonia, meningitis, and sepsis. There are two types of pneumococcal vaccines: conjugate vaccines and polysaccharide v ...

. Many other bacterial pathogens lack vaccines as a preventive measure, but infection by these bacteria can often be treated or prevented with antibiotics. Common antibiotics include

amoxicillin Amoxicillin is an antibiotic medication used to treat a number of bacterial infections. These include middle ear infection, strep throat, pneumonia, skin infections, and urinary tract infections among others. It is taken by mouth, or less c ...

, ciprofloxacin, and doxycycline. Each antibiotic has different bacteria that it is effective against and has different mechanisms to kill that bacteria. For example, doxycycline inhibits the synthesis of new proteins in both gram-negative and gram-positive bacteria which leads to the death of the affected bacteria. Due in part to overprescribing antibiotics in circumstances where they are not needed, some bacterial pathogens have developed antibiotic resistance and are becoming hard to treat with classical antibiotics. A genetically distinct strain of Staphylococcus aureus called

MRSA Methicillin-resistant ''Staphylococcus aureus'' (MRSA) is a group of Gram-positive bacteria that are genetically distinct from other strains of ''Staphylococcus aureus''. MRSA is responsible for several difficult-to-treat infections in humans. ...

is one example of a bacterial pathogen that is difficult to treat with common antibiotics. A report released in 2013 by the Center for Disease Control (CDC) estimated that each year in the United States, at least 2 million people get an antibiotic-resistant bacterial infection, and at least 23,000 people die from those infections. Due to their indispensability in Bacteria, essential persistent DNA methyltransferases are potential targets for the development of epigenetic inhibitors capable of, for example, enhance the therapeutic activity of antimicrobials, or decrease a pathogen's virulence.

Fungi

Infection by fungal pathogens is treated with anti-fungal medication. Fungal infections such as

athlete's foot Athlete's foot, known medically as ''tinea pedis'', is a common skin infection of the feet caused by a fungus. Signs and symptoms often include itching, scaling, cracking and redness. In rare cases the skin may blister. Athlete's foot fungus ...

jock itch Jock may refer to: Common meanings * Jock (stereotype), a North American term for a stereotypical male athlete * Jock, a derogatory term for Scottish people mostly used by the English * Short for jockstrap, an item of male protective undergarm ...

, and

ringworm Dermatophytosis, also known as ringworm, is a fungal infection of the skin. Typically it results in a red, itchy, scaly, circular rash. Hair loss may occur in the area affected. Symptoms begin four to fourteen days after exposure. Multiple ar ...

are infections of the skin and can be treated with topical anti-fungal medications like Clotrimazole. Other common fungal infections include infections by the yeast strain

. Candida can cause infections of the mouth or throat, commonly referred to as thrush, or it can cause vaginal infections. These internal infections can either be treated with anti-fungal creams or with oral medication. Common anti-fungal drugs for internal infections include the Echinocandin family of drugs and Fluconazole.

Algae

Algae are commonly not thought of as pathogens, but the genus ''Prototheca'' is known to cause disease in humans''.'' Treatment for this kind of infection is currently under investigation and there is no consistency in clinical treatment.

Sexual interactions

Many pathogens are capable of sexual interaction. Among pathogenic bacteria, sexual interaction occurs between cells of the same species by the process of natural genetic transformation. Transformation involves the transfer of DNA from a donor cell to a recipient cell and the integration of the donor DNA into the recipient genome by recombination. Examples of bacterial pathogens capable of natural transformation are ''

Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name, helicobacter, derives) is thoug ...

'', '' Haemophilus influenzae'', '' Legionella pneumophila'', '' Neisseria gonorrhoeae'' and ''

Streptococcus pneumoniae ''Streptococcus pneumoniae'', or pneumococcus, is a Gram-positive, spherical bacteria, alpha-hemolytic (under aerobic conditions) or beta-hemolytic (under anaerobic conditions), aerotolerant anaerobic member of the genus Streptococcus. They ar ...

''.

Eukaryotic Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the ...

pathogens are often capable of sexual interaction by a process involving

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately r ...

and syngamy. Meiosis involves the intimate pairing of homologous chromosomes and recombination between them. Examples of eukaryotic pathogens capable of sex include the protozoan parasites '' Plasmodium falciparum'', '' Toxoplasma gondii'', '' Trypanosoma brucei'', ''

Giardia intestinalis ''Giardia duodenalis'', also known as ''Giardia intestinalis'' and ''Giardia lamblia'', is a flagellated parasitic microorganism of the genus ''Giardia'' that colonizes the small intestine, causing a diarrheal condition known as giardiasis. The ...

'', and the fungi '' Aspergillus fumigatus'', ''

'' and '' Cryptococcus neoformans''.

Virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...

es may also undergo sexual interaction when two or more viral genomes enter the same host cell. This process involves pairing of homologous genomes and recombination between them by a process referred to as multiplicity reactivation. Examples of viruses that undergo this process are herpes simplex virus,

human immunodeficiency virus The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immun ...

, and vaccinia virus. The sexual processes in bacteria, microbial eukaryotes, and viruses all involve recombination between homologous genomes that appears to facilitate the

repair The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, and residential installa ...

of genomic damage to the pathogens caused by the defenses of their respective target hosts.

References

External links

Pronunciation Guide to Microorganisms (1)

Pronunciation Guide to Microorganisms (2)
{{Authority control Infectious diseases Microbiology

Pathogenicity

Context-dependent pathogenicity

Related concepts

Virulence

Transmission

Types of pathogens

Algae

Bacteria

Fungi

Prions

Viroids

Viruses

Other parasites

Pathogen hosts

Bacteria

Plants

Animals

Humans

Treatment

Prion

Virus

Bacteria

Fungi

Algae

Sexual interactions

See also

References

External links