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⛺ | Infected women also died ... Outdoor tick-borne "Japanese spotted fever" is on the rise At camps, etc. I heard from experts ...


Deaths of infected women are also increasing ... Outdoor tick-borne "Japanese spotted fever" is on the rise At camps, etc. that we asked experts ...

If you write the contents roughly
It is transmitted by being bitten by a tick that carries the pathogen "Rickettsia", but what is the countermeasure?

Autumn is a fun season for hiking and walking, but be careful of mites.Tick-borne infectious disease "Japanese spotted fever ... → Continue reading

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Pathogen(Byougentai,British: pathogenic) Means for living organismsParasiticdo itsickWake upProtozoa-Bacteria-ウ イ ル スOrganisms such as[1]..Especially among the parasitic organismsPathogenicityThose with.

Diseases caused by pathogensInfectionThat.


To understand the concept of pathogens and to determine what is a pathogen and what is notParasiticAnd the phenomenonPathogenicityIt is necessary to understand the complicated concept of.Parasitism is a phenomenon in which one organism (in this case, a microorganism) lives by utilizing the body structure of the other organism.[2]..Such a parasitic phenomenonHostSeen from the side (parasite side), many of the parasites that enter the body are so-called "pests" and are often pathogenic microorganisms, in which case they are called "pathogens".[2]..However, in some cases the parasite is not pathogenic, in which case the parasite is not a "pathogen", that is, whether a parasite is a "pathogen" or not, is it pathogenic? It depends on the judgment[2]..Pathogenicity means the ability to cause disease, but the term is complex and it is not always easy to determine whether a microorganism is pathogenic or not.[2].

Explain why the determination of pathogenicity, which is the basis for determining whether or not it is a pathogen, is complicated.The degree to which a parasite grows in the host is affected by the balance between growth-promoting factors and growth-suppressing factors in a kind of environment called the host.[2]..The growth-promoting factor is the presence of nutrients required by the parasite, the affinity between the parasite and the host, etc., and the growth-suppressing factor is possessed by the host.ImmunologyIt is a self-defense mechanism such as a system[2]..These factors vary considerably depending on whether the host is a plant or an animal, and for that matter, each one.It varies from one to another[2]..Whether or not a disease develops depends on the correlation between the pathogen and the host and the relative relationship (relationship between microbial species and organisms, relationship between microbial species and individual organisms).[2]..In this way, the determination of pathogenicity is complicated.

To complicate matters, pathogenicity is often regarded as a general attribute or characteristic of microorganisms by type, but this is not always the case, and the subtle differences between microorganisms that fall into the same species. Even if you pay attention to and compare them one by one (for example)MutationThere is a complexity that there is a difference in virulence virulence and virulence (pathogenicity) of each species (even when comparing species and mutants).[2].

The pathogen has the following characteristics.

  • The pathogen is invisible (to the naked eye and to the patient's appearance).
  • When a pathogen of a disease acts on a healthy human, the disease is developed. The disease does not develop in humans without pathogens. (Responsible factor for illness: a necessary and sufficient condition)
  • From an ill patient, it can be transmitted to another person by several routes, such as direct contact or through the air (infectious)
  • Since the number of patients (who should have the pathogen) increases due to the transmission, the pathogen itself has the property of increasing (proliferative)
  • When a patient with an infectious disease moves to another location, a new infectious disease occurs at that location (it is portable)


In humans and animals, what is called a pathogen is one of microorganisms such as viruses, eubacteria, fungi, and protozoa, which has a property of causing a disease in a host organism. In addition to microorganisms,Roundworm,NematodeHelminths such asAnimalBody) that is not visible to the patientParasiteEven often called pathogens. In some cases, extracorporeal parasites such as fleas and lice are also included in this. Although it is not a living thing, it has the same characteristics as those listed above,PrionProteins are also treated as pathogens. In plants, besides the aboveViroidHas infectivity calledNucleic acidCan become a pathogen.

Classification based on the infectious disease law

Japanese"Act on Prevention of Infectious Diseases and Medical Care for Patients with Infectious DiseasesIn Article XNUMX of Chapter XNUMX, General Provisions (Definition), pathogens of infectious diseases andtoxinAre classified into specific pathogens, etc. from type XNUMX pathogens, etc. to type XNUMX pathogens, etc., and pathogens, etc. that do not correspond to specific pathogens, etc.

One pathogen
Having pathogenicity, it will contribute to the lives and health of the people.extremelyPathogens that may have a serious impact (Article 19)
Two pathogens, etc.
Having pathogenicity, it will contribute to the lives and health of the people.SeriousPathogens that may affect (Section 20)
Three pathogens, etc.
Pathogenic andlifeAnd pathogens that may affect health (Section 21)
Four pathogens, etc.
It is pathogenic and may affect the health of people.あるPathogens, etc. (Section 22)
Pathogens that do not correspond to specific pathogens
Pathogens that are pathogenic and may not be said to affect the health of the people

History of research, history of understanding

Infectious diseases, especially human-to-human or animal-to-human transmissionEpidemicHas long been feared as a threat to human health, but it has been unclear why these infectious diseases occur until the early modern times. Advocated in BCMiasma theoryWhen,16st centuryAdvocated byContagion theoryThe two hypotheses have been controversial for a long time,19st centuryToRobert KochSucceeded in experimentally demonstrating the existence of pathogenic bacteria for the first time, and is the successor to the contagion theory.Bacterial theoryI got a war. After that, it became clear that many microorganisms became pathogens, including the discovery of viruses.

Miasma theory and Contagion theory

In the old days, infectious diseasesNatural disasterIt was thought to be a kind of divine punishment, but it spreads irrespective of status, race, etc. and concentrated in one place, and sometimes it spreads across multiple countries of different beliefs. Therefore, this idea was gradually denied. AndHippocratesWas active4th century BCBy the timeMiasma theory(AspirationThe theory called) was advocated. The Miasma theory is that human beings get sick by touching the air polluted by some cause (mache, Miasma). Although the existence of "mite", which forms the core of this theory, has been denied since the 19th century, it was important for medical science to first propose the basic concept of a pathogen that "a disease is caused by an exogenous causative substance." It was a turning point. These old ideas have long been believed, and even todaymalaria(ItalianDerived from mal aria, which means "bad air",influenzaThe remnants can be seen in the disease names such as (from the meaning of being affected by the celestial body operation and cold air).

14st centuryから16st centuryOversmallpox,Plague,syphilisOutbreaks such asEuropeWhen the disease occurs in Japan, the infection may spread as the patients with these infectious diseases move, and the existence of "something that mediates the disease" that cannot be explained by stigma has become vaguely recognized. ..1546/,Girolamo FracastroPushes this idea further,Contagion theoryProposed (contact contagion theory). Among them, Fracastro has been shown to develop the disease by contact with living infectious organisms (contagium vivim, contagium animatum), and further spread by being transmitted to other humans. Furthermore, Fracastro has three forms of this transmission: (1) by direct contact with the patient, (2) through some vehicle, and (3) transmitted by a remote patient (airborne). The mechanism by which the infectious disease spreads was explained by classifying into. This theory not only predicted the body of the pathogen as a living organism, but also accurately predicted its transmission. From a modern point of view, it was found that the Contagion theory, rather than the Miasma theory, was closer to the truth, but at the time, even Fraccastro's theory could not be scientifically proved. For this reason, the Miasma theory and the Contagion theory were treated as mere hypotheses without much proof of mutual controversy, despite many controversies. People in those days eventually came to think that the types of illness could both be caused by miasma or contagion.

Bacterial theory and environmental theory

On the other hand, completely independent of this medical trend,17st centuryToRawen Hook MicroscopeVarious withmicroorganismWas discovered, the academic field called bacteriology (microbiology) was pioneered. However, the bacteriology at that timeNatural historyThese studies are mainly based onmicroorganismHowever, it seems that he had no idea that he had something to do with human life.18st centuryBy the end of the year, with the progress of microbiology, the knowledge that specific microorganisms already exist in the pathological tissues, blood, and feces of patients with infectious diseases accumulated, and for medical researchers who supported the Contagion theory. It was an important argument. However, at that time, the bacteria were still isolated and pure.cultureSince the technology for doing so was not established, the counterargument of the Miazuma theory supporters could not be evaded, and it was not possible to prove conclusively.

19st centurybecome,Louis PasteurEstablished a liquid culture method for bacteria, and made a great contribution to the progress of bacteriology. Initially, he was from the field of brewing, not medicinefermentationInvolved in the research ofNatural theoryHowever, it was clarified that the activity of microorganisms had an unexpectedly large influence, and that it was scattered in the air in large numbers.corruptionI found that I was involved in human life from both the harmful side and the other side. Furthermore, he developed this idea in the medical direction, and a type of spoilage substance produced by microorganismstoxinI advocate the theory that it may cause diseases by acting on humans, that there are many microorganisms in the dust in the air, what dangerous things may be contained in them Announced their concerns. The idea of ​​this Pasteur supports the theory of Contagion, and it is the theory that bacteria are the body of the "living infectious organism" that the Contagion theory says.Bacterial theory) Has shown a new concept. At the same time, by clarifying the phenomenon of decay, it was also intended to explain the mechanism of its pathogenicity.

1865, South PasteurFrance OfsericultureFrom a supplierSilkwormHe was asked to provide guidance on how to deal with these diseases, and discovered the microbes that cause the particulate disease that causes them. It is also said to be the first pathogen discovered. However, Pasteur's liquid culture method could only cultivate in a state where multiple bacteria were mixed, and it was not possible to isolate and culture the pathogen alone, so this is also not an experimental demonstration of the pathogen. There wasn't.

The discovery of the corruption phenomenon by Pasteur was not a definitive proof, but it was a great support for the Contagion theory. But to this,Max von PettenkoferIncorporated the discovery of Pasteur into the traditional Miasma theoryEnvironmental theoryHe proposed and proposed a new concept called. Petten coferSewerBecause of the achievement of stopping various outbreaks of epidemics through the maintenance of the above, he supported the Miasma theory, which is easy to explain the relationship with environmental (especially soil) pollution. Pasteur's theory of bacteria was that (1) bacteria infect humans, (2) produce spoilage substances in the human body, and (3) the spoilage substances become toxins that cause illness. In contrast, Pettenkofer said that (1) bacteria in the human body (which are not pathogenic as they are) are excreted, contaminating soil and water, and (2) contaminated bacteria multiply in soil and water. Then, he created the idea that (3) the putrefactive substance acts as a miasma on humans to cause illness.

Experimental proof by Koch

Slightly behind the Pasteur,Germany OfRobert KochStarted research on bacteria as pathogens in the field of medicine. Koch cutpotatoThe liquid medium is used as a hint of how mold grows in the cross section ofgelatinThe solid culture method of bacteria was established by inventing a solid medium solidified by. Unlike the liquid culture method, the solid culture method is different from the mixture of pathogenic bacteria and other bacteria, which are independent of each other.colonyAs a result, it became possible to perform pure culture by isolating the bacteria as described above, and finally, it became possible to study the pathogenicity of only one isolated bacteria.

Koch was one of his teachers when he was a student, using this techniqueJacop HenleOf the three principles required to prove pathogens proposed byHenle's principle, Corresponded to Koch's principle 1-3), and worked on the proof of the bacterial theory. And1876/ToAnthraxSeparated from the animal that causedAnthraxHas been demonstrated to meet Henle's principle of pathogenicity. He also proved that after this, anthrax could be isolated from the body of experimentally infected animals (corresponding to the fourth condition of Koch's principle), and experimentally proved that the bacterial theory was scientifically correct.

Furthermore, Koch1882/To the humantuberculosisAs a pathogen ofMycobacterium tuberculosis, And experimentally proved that the bacterial theory was correct for human diseases. At the same time consists of 4 conditionsKoch's principleWas announced. This principle consists of the following four conditions.

  1. Finding certain microorganisms in certain diseases
  2. Being able to isolate the microorganism
  3. Infecting susceptible animals with isolated microorganisms to cause the same disease
  4. And that the same microorganism is isolated from the lesion

Meeting all four of these requirements is a strict requirement for a microorganism to be the pathogen of a particular disease. As a result, the interest of medical researchers was immediately drawn to bacteriology, and by the beginning of the 4th century, the pathogens of major infectious diseases had been discovered.

However, due to medical progress since Koch, even if all of these conditions are not met (only two or three conditions are met), some microorganisms have been recognized as pathogens, along with findings from other epidemiological studies.

Meanwhile, Pettenkofer, who supported the environmental theory,choleraDisagree with the theory that the pathogen of1892/ToCholeraDrink yourselfSelf experimentI tried to prove the correctness of my theory by doing. As a result, Pettenkofer himself suffered severe diarrhea, but was regarded as the main symptom of cholera.DehydrationSince it did not occur, it resulted in a claim for the correctness of the bacterial theory. However, after that, from the results of additional tests by other researchers, it becomes gradually clear that whether or not the disease is caused depends on the balance between the virulence of the pathogen and the resistance of the host. In addition, the bacterial theory was proved to be the more correct theory, and the long-standing dispute with the environmental theory and the Miasma theory was settled.

From the discovery process, it was thought that all pathogens were bacteria in the 19th century, but after that, their classification proceeded with the development of microbiology,Eubacterianot onlyFungi,ProtistsAlso, the nature of causing disease in the host (Pathogenicity) Was found. In addition, pathogenicity remains even after passing through a unglazed ceramic filter that can remove bacteriaFilterable pathogenAs,ウ イ ル スIt was revealed that the pathogen contains various microorganisms and viruses in addition to bacteria.

History of discovery of major pathogens

Disease nameYear of discoveryPathogen discoverer
Leprosy1875/Almawell Hansen(Norway
Anthrax(Anthrax1876/Robert Koch(Germany)
malaria1880/Charles Louis Alphonse Lavrain(France)
typhoid1880/Karl Abelt(Germany)
tuberculosis1882/Robert Koch(Germany)
cholera1883/Robert Koch (Germany)
Diphtheria(diphtheria1883/Emile von BehringKitasato Shiba Saburo
tetanus1884/Arthur Nicolaier(Germany)
Brucellosis1887/David Blues(United Kingdom
Plague1894/(French version(France),Kitasato Shiba Saburo(Japan)
dysentery1898/Kiyoshi Shiga(Japan)
syphilis1905/(German version(Germany)
Social Services Lizard1906/Jules Bordeaux(France)
typhus1909/Charles Jules Henri Nicole(France)

History of measures

The oldest effective and effective countermeasure against pathogensJenner vaccinationHe developed the law, but he could not apply it because he had no understanding of its mechanism.Joseph ListerbydisinfectionThe law is手術Due to bacterial infection duringsepticemiaAlthough it had a great effect in suppressing the occurrence of such diseases, it also cannot cope with general infectious diseases.

The discovery of the pathogen clarified the targets for which measures should be taken, but it did not mean that specific countermeasures were actually discovered. Whether it was Pasteur's silkworm particle disease or Koch's discovery of B. anthracis, the idea was to consider individuals with pathogens and those in contact with them.burnOrfill inThis is almost the same as the measures taken before that. Only slightly, Koch's finding that Bacillus anthracis does not work at low temperatures only reasonably supports.

The first really useful countermeasure is Pasteur's anthraxvaccineIs the development of. This is basically the same as for smallpox, but first inoculates the attenuated pathogen to the animal body.ImmunologyIt was possible to apply it because it was possible to theoretically support it. He thenRabies,Chicken choleraHas also developed a vaccine. Many by this technologyEpidemicAgainstvaccinationIt became possible to compete with. Also, by Kitasato et al.Serum therapyIs based on this principle, but the range of applications is greatly expanded.

Vaccines use the mechanism of human body defense, but it was discovered as a method to directly attack pathogens against this.penicillinIs. In 1929Alexander FlemingIt is,Blue moldWas observed to inhibit the growth of bacteria, and the chemical substance responsible for this was taken out and named penicillin. This material is especiallyGram-positive bacteriaShowed a strong effect on. Inspired by this, secreted by microorganismsAntibioticsThe search is started,ActinomyceteFound fromstreptomycinAnd many things have been discovered and used.

Why pathogens continue to exist as pathogens

If the host stays alive and well, the parasite will preserve the environment it needs to keep going, and if the host is killed, that environment will disappear.Such pathogenic parasites continue to live for generations, even though this illness and death of the host seems to work against the parasite in terms of "survival." The possible reasons are as follows.

  • Of the hostPharynx,Nasal cavityBy breeding in the host and actively causing diseases in those areascough,sneezeIt ’s better to have them doAirborne,Aerosol infectionSince it can be done, it is rather advantageous for propagation.Also of the hostcolonBreeding indiarrheaAlso, a small amount of stool may stick to the area around the buttocks or surrounding objects, increasing the chances of contact with surrounding host candidates (even in humans, it may adhere to underwear or indirectly after several steps. It is more likely to be transmitted to other humans by adhering to other humans in a small amount), which is also rather advantageous in reaching many hosts.Besides, this is a simple math problem.If the index of how many individuals one host infects is 1 or more, the parasite will continue to survive for the time being, and if the effective reproduction rate is higher,Mouse arithmetic(Exponential series) It will proliferate.Even if you kill the host with a certain probability, you can secure a certain period until the host dies, and increase the number of new hosts in parallel with the period of illness. For example, parasites can grow macroscopically.So, in summary, developing certain diseases has a significant advantage in increasing the transmission of parasites, and thus the host is the host for the increased transmission (increased effective reproduction rate). The difference between staying alive and dying becomes a fairly small issue, and it continues to proliferate even if it propagates and kills the host, that is, uses the host "disposable".
(However, killing the host does not cause much disadvantage only when the transmission power is high. ComputersimulationAs you can see by doing such things, if the effective reproduction rate is less than 1, but it seems to kill the host too much, the parasite (mutant) has a short time to annihilation, in a broad sense. Become.Also, if a mutation occurs that kills the host too quickly immediately after infection and reduces the chances of transmission by itself, it will work against you, accelerating the reduction, and if there is competition between the mutants, In principle, it loses the relative competition with the mutants that have obtained high transmission power by making the best use of the host, and disappears without a hitch. )
  • Usually it does not cause damage, but if the host's health is not good, damage will occur. normallySymbiosisAlthough it can be said that there is a relationship that causes illness when the host's physical strength is reduced,Opportunistic infectionCalled.

As a parasite that kills the host,昆虫Often seen inParasitismThere is a type. On the contrary, it has the characteristic that it always kills the host,PredationIt is said to be located in the middle of. this isLife historyIt kills the host during certain stages of, but differs in that the pathogen does not necessarily have to kill the host. However, some parasites such asFungiIs sometimes called either.


Use by living things

Some living things use pathogens for natural enemies in their bodies, so-called, in order to keep them away from their natural enemies.


There is a method of using a pathogen for humans as a kind of weapon, infecting the enemy, killing the enemy or making it incapable of fighting.Biological weaponsIt is classified as.

Historically, the method used by Alexander the Great has also been documented.Alexander the Great commanded his subordinates,PlagueWhen the patient's pathogen-covered clothing was sneaked into a well that many enemy soldiers would use, the ignorant enemy soldiers drank the water and enemies, as intended. It is said that the infection of Pest spread with a tremendous force in the army, and it became incapable of fighting and devastated, and Alexander the Great was able to defeat the enemy army without engaging.


  1. ^ Shogakukan "Digital Daijisen"
  2. ^ a b c d e f g h i Encyclopedia Nipponica, [Pathogen]

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