About structuring the study of parasites

Of all the infectiological disciplines parasitic lore is the one whose special field includes the most colourful variety of ways. Because parasitism, perceived as a life form, is as old as cellular life on earth if organized in cellular units - if attributing parasitic RNA pieces also to parasites, parasitism is older than life itself. Excluding for conventional reasons these - today as "jumping genes" presenting - units and the prions, all "cadgering" biological entities are parasitic, because viruses, infectious malignant cells (canine transmissible venereal tumor, the Devil Facial Tumour Disease of the Tasmanian devil), bacteria, fungi, plants, protozoa, worms, as well as blood-sucking and lytic "higher" taxa exist through energy robbery, usually food robbery, without killing their host at once (ie, before or during the energy robbery) - even if they are rarely causing a disease which is leading to the death of the host lateron. Sometimes mistakenly regarded as "dead end" of evolution, parasitic units in truth are evolutionary highly successful, if not the most successful way of life on this earth. 30% of all animal species described are parasites. These animals have colonized every ecological niche on earth, they have survived every geological change and every era and eventually adapted to any protective measures of the hosts. Though parasitic lifestyles can be found within members of all the kingdoms of life, not all of these organisms are counted to the parasites sensu stricto:

The virology, bacteriology and mycology have become autonomous fields, the in the reception of the term historically preferential botany authorized the common use of the word, and all fields have left a salmagundi of not by them registered pathogens, pests, and vectors that are called parasites (sensu stricto) in the medical sciences, respectively. Them is nothing more in common than that, by definition, to be an eukaryotic, heterotrophic organism without a cell wall, that the host must belong to another biological species than the parasite, and that the Darwinian evolution rules can be applied to a large extent. Within the core area of the term "host of a parasite" lies undoubtedly man, Homo sapiens Linnaeus, 1758 (medically relevant parasites), and livestock, domestic animals, and pets (veterinary medically relevant parasites); as well as most other eukaryotic, heterotrophic organisms without a cell wall. In the outer area, however, are the plants. The Eubacteria, the Archaea, and the fungi are mostly outside of the term as commonly accepted. Certainly not within the area of the term belong the feeder on animal colonies and herbivores. This usual classification is, however, illogical and explicable only by the widespread disgust with these animals.

In medicine by historical reasons under the term parasite only animals are subsumed, which belong to the zoological taxa (mostly phyla = "blueprints") Protozoa, Platoda (Trematoda & Cestoda), Nematoda, Acanthocephala, Annelida, Arthropoda and Vertebrata.

Distinguish carefully a parasite infestation, a colonization of a host by a parasite with no apparent damage, and a parasitosis, a disease caused by an infection with a parasite. All thoroughly studied, as hosts suitable organisms are colonized by parasites. Most of them do not make the host sick, however. If this colonization is considered as pathological, there would be no "healthy" animals in the wild and no healthy human beings. Only in the case of a clinically manifest disease a parasite infestation is a pathological phenomenon and needs treatment generally.

The parasitology is the apprenticeship of an (animal) community to the detriment of the one and for the benefit of the other party, and thus a special case of the community ecology, the study of the relationships of organisms with each other within a community.

Definition of an opportunistic parasite: Opportunistic microorganisms are microorganisms that may or may not cause disease in the host. They generally colonize, but do not infect the host. Either an invasion or the multiplication and/or the answer of the immune system is lacking. In cases of an usual association with a host organism, they may be seen as a common microbiota. But, they can cause severe, even lethal disease if they are inadvertently introduced into a site, where they do not usually reside. This is the case if they invade unusual host tissues and/or if the immune system of the host is damaged. Because of the lowered immune answer, immunosuppressed persons or vertebrates are highly endangered by opportunistic infections. However, dependent on the type of the immunosuppression, the degree of endangerment is different. Opportunistic microorganisms are not detectable in expulsions of healthy adults, or, if they nevertheless arise, immunocompetent adults very quickly clear the colonization and do not get sick at all.

The parasitological knowledge of prehistoric man may probably have resulted substantially from the own behaviour and from that of observable mammals that served as a systematic discarding of ectoparasites perceived as troublesome. Considering the evolution of man a positive feedback effect is undisputed between an interpersonal removal of lice ("grooming") and the formation of groups and group cohesion. Whether specific pharmacologically active food components were consumed to reduce the Ascaridian burden at least, is controversial; similar to observations in chimpanzees such considerations can definitely be postulated. Only in the case of the Guinea worm the traditional cultural notes and the etiological logic are strong enough pronounced to hypothesize a prehistoric perception of the "foreignness" of this parasite and its harmfulness to human health.

Culturally and historically interesting is the relationship between the art of hieromancy which is the viscera inspection, here specifically the inspection of the liver, and an actual infestation of farm animals by parasites. Developed between the 20^th and the 10^th century BCE and of enormous charisma, this art was still used in the early Roman oracles. It seems therefore to have obviously reached a certain, beneficial accuracy. Though the Haruspex deduces by means of very sophisticated knowledge sets via an exact exploring the surface of the liver of the sacrificial animal the will of the gods. Especially in the region where this art was developed, in Mesopotamia, the most common application seems to have been temporary, agricultural issues. Explicitly codified as relevant evidence are changes that we associate with the activity of liver parasites today (cit. Maul 2005). The traces left by the migration of larvae of nematodes and trematodes, the changes of the bile ducts by liver fluke infestation, and destructions caused by tapeworm larvae can undoubtedly be correlated with fertile, moist years and/or high livestock. The relationship with human well-being and productivity of the community will be understandable even today.

From a today´s perspective, the more millennial view on the "reversed" cause-effect relationship of (infectious) diseases is somewhat problematic. Already in Chinese medicine writings, the book Su-Wen, from the mid-26^th century BCE there is an obvious description of scabies with instructions for removing the mite. The mite is however not regarded as the culprit but as a result of the disease (cit. Theodorides 1980). This idea, explained by the social circumstances and from the observation of persistent recurrent disease (nowadays re-infection due to the circumstances), maintains itself via the "European" four-humours-doctrine (humouralism) to this days in the form of the Traditional European Medicine (TEM). In biblical (Old Testament), Jewish and partly fundamental Christian thoughts a disease and the consequences of an illness is a punishment from God for evil deeds or for a failed life. This approach is particularly vulnerable to the search for a culprit, a villain, a hater of God, such as King David, whose deeds provoked an epidemic in Israel. In the Roman Catholic thinking the disease is not punishment and therefore the will of God, but an evil approved by God, often caused by sorcerers or witches allied with Satan.

Historically, for a long time a purely descriptive and therefore intellectually unsatisfactory "parasite skill", often in parallel with the above-mentioned sequence theory, be determined: The controversial parasite-associated citations of the Ebers papyrus (ca 1500 BCE), which names the ààà disease, possibly a dracunculiasis (cit. The Wellcome Trust 1996), the "fiery serpents" of the book of Numbers (ca 800 BCE), the Hippocratic flatworms, roundworms and ascarids (= pinworms) (cit. Hippokrates of Kos, ca 460-370 BCE), the Aristotelian "hailstones" (= cysticerci) of the pork (cit. Aristotle, 384-322 BCE), the intestinal worms and ticks in the Historia naturalis of Pliny the Elder (23 -79 CE), and the mentioning of the deadly sleeping sickness of the Emperor Mari Jata of Mali by Ibn Khaldun (1332-1406) (cit. The Wellcome Trust 1996) are described as pure observations, any correlation with an infectious entity is not established. Numerous Byzantine, Arab and medieval writings contain more or less accurate descriptions and lists of parasites of humans, the number of the forms described, today called biological species, continuously increases because in Europe each older text is recognized as a source of priority, and each author inflicts own knowledge. Even the first known book, which deals only with parasitic worms, Hieronymus Gabucinus´ De lumbricis alvum occupantibus ac de ratione curandi eos qui ab illis infestantur [1547], is a largely descriptive work; nevertheless in it the view is taken that a cooling of the intestine leads to the emergence of tapeworms, which are then ejected during fever periods.

By contrast, from the view of Aristotle that lice and fleas emerge from dirt and sweat develops the hypothesis of a spontaneous generation of microbes, which was recognized due to the superior authority of Aristotle until the 19^th century. In the Dictionnaire de medecine of the (nearly) physician Émile Paul Littré (1801-81) of [1878] a citation is still found, that claims a parasitogeny in "frail and weak-minded beings". A final fatal strike against this hypothesis led at first or already Francesco Redi (1626-97), who showed in his work Esperienze intorno all generazione degli Insetti [1668], that destructive maggots derived from eggs and not from a spontaneous generation in a cadaver.

According to Ackerknecht [1979] the idea, that the epidemic occurring diseases are transmitted by infections and are caused by microorganisms, "seeds" or small animals, is very old, and it is recurring stylish in irregular cycles in the medicine. In fact, Marcus Terentius Varro, called Reatinus (116-27 BCE) writes in his work on agriculture Rerum Rusticarum (lib. I, cap. 12.) the following words on infectious pathogens: "animalia quaedam minuta, quae non possunt oculi consequi et per aera intus in corpus per os ac nares perveniunt atque efficiunt difficilis morbos . . ", translated: "Animals that are so small that the eye cannot see them, and passing through the air into the body through the mouth and nose and cause various diseases". This view was indeed considered with imperial support by the Imperator Augustus´ main architect, Marcus Vitruvius Pollio (ca 65-10 BCE), in the construction of homes in malaria areas; but it could not prevail against the all-covering Galen´s humouralism until the 19^th century.

The medieval construction of separate municipal infirmaries and quarantine stations for travellers must be seen in connection with the epidemiological memory verse by Bernard of Gordon (1258-1318]: „Febris acuta, Phthisis, Pedicon, Scabies, Sacer ignis, Anthrax, Lippa, Lepra nobis contagia praestant” in English: Acute fever (= typhus), pulmonary tuberculosis, epilepsy, scabies, ergotism (= Anthony´s fire), anthrax, trachoma and leprosy are known to us as contagious (cit. Winkle 1997). Even the escape from the urban plague in the "healthy" chalets can only be explained from the assumption of an infectivity of the Black Death independent of God´s oeuvre (cit. Boccaccio 1353). One century later, however, only an infection associated with a demon´s opus approved by God was firmly anchored in the consciousness of the academically educated - ie an epidemic demonical possession (cit. Henricus Institoris 1486: I.18.42vb). But, the personal physician of three popes, Giovanni Maria Lancisi (1654-1720) noted that the number of fatal malaria cases fell sharply after the marshes were drained around Rome; whence in his script De noxiis paludum effluvis, eorumque remediis libri duo in 1717 he unsanctioned came to the conclusion that mosquitoes acted as vectors of pathogens, in doing so he postulated a "harmful substance" as the transmitted agent - and he negated with a square refusal any admission of evil by the omnipotence of God. However, these views about the contagiousness were considered as completely obsolete and as an anachronistic mistake in the first quarter of the 19^th century, because the ineffectiveness of quarantine measures had putatively been proven irrefutable in yellow fever and typhus and cholera.

When in 1840 Friedrich Gustav Jacob Henle (1809-85) reintroduced the terms contagium vivum and contagium animatum and, thus, renewed the theory of microorganisms as the culprits of infectious diseases, he was not a precursor of a new era, but he was considered as old-fashioned. For example, in 1849 Carl Ludwig Sigmund (1810-83), hygienist of epidemic diseases at the k.k. General Hospital, thought that the plague is non-"contagious" and he also expresses the strong belief that the transmission successes only by the "atmosphere of the sick" (sic!). Withal it was 1836 when A. Donné demonstrated Trichomonas vaginalis as an overt infectious agent, then the second one testified in the world. The rise of a parasitology based on the idea of contagiosity took place in the second half of the 19^th century in close entanglement with the development of powerful microscopes. The longest pendulum swing towards a pure contagious theory happened in 1884, when, for the first time and for the time being cursorily, some theses were announced from Berlin, that were later called Henle-Koch´s postulates:
Basically it applies in Medical Microbiology, if
1. a microorganism can be isolated from an infected host (ex vivo), and
2. a microorganism can be cultured in the laboratory (in vitro), and
3 a microorganism causes a similar disease to occur in each host, if this host can be infected with the microorganism, and
4. a microorganism infecting this experimental host can be re-isolated,
then, and only then, the microorganism is considered to be the culprit of a disease (= pathogen) and the disease caused by it is referred to be an infectious disease.

This linear, stringent formulation of a parasitic cause-effect relationship, embedded in a mechanistic worldview, were thought to form a supportive theoretical foundation for the military/sanitation-police-applied hygiene of the time; but already at the time of their formulation the postulates, were with such exceptions, which - viewed objectively - would have falsified the theory (eg mycobacteria). Today, the postulates are cited as a historical reference in papers about infectiology since AIDS, autoimmune diseases and opportunists have largely relativized them.

A new aspect in this old cause-effect debate was introduced by the creation of the hygiene hypothesis. This hypothesis states that the occurrence of various immunological disorders that have been primarily observed in humans at the last century such as Crohn´s disease, or the increase of the incidence in the era since hygiene measures were applied in developed countries, is attributable to the fact, that the load with parasitic worms is too low in childhood and therefore the immune system is not conditioned in time and not enough. At least some of our parasites turn out accordingly as "good guys" and their accommodation is useful for human health, they would then be regarded as symbionts! An acceptable parasitism could then be regarded as physiologically, a view that has incalculable effects on the strict malfunction concept of Western medicine. If this hygiene hypothesis is true, then it also results in the consequence, that individuals with an existing helminthic infestation have a significantly poorer immunological response than non-parasitized persons. Thus, the economic justifications of vaccination programs in the tropics should be reconsidered.

The term Dermatozoa-​delusion goes back to von Ekbom [1938] who gave distinction to it in his article Der präsenile Dermato­zoenwahn. It is an organic psychosis, a cognitive disorder with tactile hallucinations. Sufferers have the delusional idea that parasites just located at the limit of visibility, usually worms or arthropods, are under their skin and/or move around there. This leads to severe anxiety and itching, which is usually combated with uncontrolled scratching. Patients are the immutable belief that they are infested with parasites, and the doctors or parasitologists generally provide incorrect diagnoses and are especially overwhelmed in their case. The absence of any clinical or parasitological evidence is not seen as a calming and clarification, but rather as a confirmation of their opinion, that their health is threatened by some undiscovered parasites. This resulted in 2002 in Pittsburgh / USA in a "renaming" of this syndrome as Morgellon Disease by biologist Mary Leitao, who believed her child to be affected by such mysterious intruders. She founded ado the Morgellons Research Foundation, to study what doctors and scientists did not seem to care for her inexplicably. But after a decade of wasted resources the CDC itself and the Mayo Clinic came to unanimous conclusion that "the invaders are not in the skin of those affected - but in their heads." The known reasons of the syndrome include cocaine and amphetamine abuse, alcohol withdrawal, CNS diseases and brain injuries. It is assumed that the delusion is related to the hormonal changes during the menopause. It affects more persons older than 40 years and more women than men. The diagnosis is usually not difficult, as the perceptual distur­bances are obvious; the assignment of the patient to a specialist psychiatrist is usually impossible because of a lack of such psychiatrists and the fierce resistance of the patient. A treatment is often futile due to the lack of compliance because the patient almost always decide to refuse a psychiatric cause of their suffering and unshakably trust in somatic causes. Not infrequently, this situation will be exploited by charlatans and healers of all kinds, and even by fraudulent researchers as a supposedly risk-free playground (cit. Shelomi 2013) and the sufferers are exploited as an enrichment spring.