PARASITOLOGY: HISTORY, WHAT DOES IT STUDY ?, BRANCHES, CONCEPTS - BIOLOGY

The parasitology is the scientific discipline derived from biology that is responsible for studying the biology of parasites and diseases caused by them. Those who engage in such studies are known as parasitologists.

This branch of biology studies the distribution, ecology, evolution, biochemistry, physiology, molecular biology, and the main clinical aspects of parasites, as well as the host's response to these agents.

Scolex from Taenia saginata, a human endoparasite (Source: CDC DPDx / Public domain, via Wikimedia commons)

Therefore, it is understood that this branch of science generally focuses on the study of the detrimental effects that organisms that live in or on another living organism have, and not just the mere interaction between a parasite and its host.

Although parasites can belong to any group, including bacteria, yeasts, fungi, algae, viruses, protozoa, helminths and arthropods, parasitologists focus particularly on internal zooparasites, that is, on endoparasites that affect animals.

The study of viruses, bacteria and fungi that affect animals, plants and microorganisms is therefore a concern of microbiologists.

History

The history of parasitology is "distributed" between different disciplines, especially zoology. Furthermore, it is important to highlight that the advent of microscopy was of great importance for the development of this science.

Many intestinal parasites that affect humans have been known for centuries, and interest in their study began in Europe around the 17th century.

Spontaneous generation

Initially, there was a general belief that parasites arose by "spontaneous generation", either inside or outside any living organism. It was during the seventeenth century that William Harvey and Jan Swammerdam, detractors of this doctrine, argued that it was not true.

Later, Antony van Leeuwenhoek stated that corn weevils did not arise by spontaneous generation and Francesco Redi discarded the theory that flies arose spontaneously from meat.

Anton van Leeuwenhoek is considered one of the main precursors of microbiology. Source: Jan Verkolje (1650-1693)

Edward Tyson showed that there were two sexes of the parasite A. lumbricoides, establishing the fact that they multiplied by sexual reproduction and did not arise by spontaneous generation. So on, other scientists of the time definitely abandoned the foundations of spontaneous generation.

Beginnings of parasitology as a "specialty"

Francesco Redi is considered, perhaps, the "father of parasitology" and was particularly interested in ectoparasites. His most famous text was "Observations around living animals found within other living animals."

Portrait of Francesco Redi (Source: Valérie75, via Wikimmedia Commons)

Nicolas André, author of the text “From the generation of worms in the body of man” in 1699, was also a pioneer in the area and was the first to illustrate the scolex of the flatworm Taenia saginata. This author associated these worms with venereal diseases, but their cause-effect relationship lasted.

In the 18th century, one of the main figures in the field of parasitology was Pierre Pallas, who wrote “Zoological Miscellany”, a text especially focused on gallbladder worms, all considered to belong to the Taenia hydatigena species.

Johan Göze, an amateur naturalist, also made numerous important contributions to helminthology (the study of helminth parasites).

The era of the 19th century

During this century important texts on helminthology came to light and much interest was directed to the parasitic worms of humans Taenia solium and Taenia saginata. The "birth" of modern parasitology is said to have occurred in this period.

Felix Dujardin was one of the most distinguished parasitologists of this century. He was one of the first to consider trematodes and tapeworms as parasites in intermediate hosts. He introduced the term "proglottid", which means "segment of a flat or ribbon worm."

Later on, numerous scientists set the tone in the area, contributing significantly to the discovery and description of many human and animal parasites, as well as the diseases caused by them.

What does parasitology study? (object of study)

Parasitology, as mentioned at the beginning, is the branch of biology that is responsible for the study of the relationships between parasites and their hosts. It is mainly focused on the harmful effect that parasites have on the organisms that host them and on the characteristics of both.

It emphasizes characteristics of parasites such as their morphology, their life cycle, their ecology and their classification, among others. In addition, it has to do with the study of the types of hosts and the close relationships and evolutionary aspects between them and the parasites that colonize them.

It works in conjunction with tools from other disciplines such as entomology, helminthology, epidemiology and others.

It focuses mainly on the study of parasites belonging to the following groups:

- protozoa (single-celled organisms such as mastigophores, sporozoans, sarcodins, ciliaphores)

- helminths (multicellular organisms such as cestodes, trematodes and nematodes) and

- arthropods (bilateral and symmetrical multicellular organisms that have appendages for movement, examples of these are ticks, fleas and others that are transmitters of other parasites)

Graphic representation of a tick (Source: JaviMoreno16 / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0), via Wikimedia Commons)

Branches of parasitology

Parasitology, considered by some authors as a branch of ecology, can be divided into several "fields" or "branches" of study, among which are:

Medical parasitology

This is one of the most popular branches of parasitology, since perhaps one of the best known aspects of parasites is their participation in the development of different human diseases.

Medical parasitologists use different approaches to deal with parasites. Research areas that serve as a tool for this purpose include:

- epidemiology, which is the study of factors that affect the health and disease of individuals and populations

- chemotherapy, which is the use of chemicals to treat diseases

- immunology, a branch of medical sciences that deals with the study of all aspects of the immune system in all living things

- pathology, which is the study of the processes underlying disease, harmful abnormalities or dysfunctions

At the same time, medical parasitology is closely related to the field of public health.

Veterinary, agricultural and aquaculture parasitology

This branch of parasitology is responsible for the study of parasites that affect other animals in addition to humans, mainly domestic and farm animals, with high economic interest.

It is an important branch of parasitology, since the health of humans is not only affected by specific parasites of man, but can also be indirectly affected by parasites that cause diseases in plants and animals that are a food source for man.

Structural parasitology, biochemistry and molecular biology of parasites

It is a branch of parasitology that focuses on the chemical and organic structures that make up parasites at the subcellular level: proteins and enzymes, nucleic acids, organelles, membranes, etc.

Its ultimate goal is the acquisition of a better understanding of these structures, especially in comparison with their counterparts in humans, for the discovery and / or design of antiparasitic drugs.

Parasite ecology and systematic parasitology

This or these branches of parasitology are in charge of various aspects of the life of parasites:

of the ecology of parasite host populations
ecological strategies used by parasites to colonize their hosts
of the evolution of parasites
of the interaction of parasites with the environment through their hosts
of its taxonomy (classification) and systematic (diversity of characteristics)

Immunoparasitology

This is the branch of immunology and parasitology that deals with the study of the immune responses of hosts against invasion by a parasite.

It is of great importance in the development of specific vaccines against parasites that affect humans and domestic animals, which generally translates into an extension of life expectancy for them.

Basic concepts in parasitology

The study of parasitology implies the handling of a series of "basic" concepts:

Parasitism

It is a symbiotic relationship between two individuals of different species where one of them, the host, is harmed by the presence and activities of the other, the parasite.

Parasite

Any organism of a species that maintains sustained contact with an organism of another species (on it or inside it, intracellularly or not) and that benefits from the former by deriving nutrients at its expense.

It is generally understood as an organism that "takes advantage" of another to the detriment of this, so its presence and / or interaction has detrimental effects on the host species.

Parasites can be obligate, facultative, accidental, or erratic, depending on their relationship to the host.

Furthermore, they are classified as ectoparasites (external or superficial) and endoparasites (internal) based on their location in the host's body.

Host

Any organism that supports the life of a parasitic organism, providing shelter and food. There are intermediate hosts and definitive hosts, as well as hosts that act as "reservoirs."

Intermediate host: it is an organism that a particular parasite uses during its life cycle to multiply asexually
Definitive host: that organism where the parasite reproduces sexually
Host “reservoir”: organism of a species in which a parasite that affects another species can live and multiply without causing any harm to the host.

Vector

The host of a parasite that serves as a transmitter of the parasite to its definitive host and that, therefore, is an essential part of its life cycle. It is a term widely used to refer to those organisms that are pathogenic parasite transmitters for humans.

Lifecycle

The series of "steps" or "stages" through which an organism passes recurrently throughout its life; usually begins with a specific primary stage. It refers, then, also to the reproductive cycle of an organism and to the different stages that it includes.

In the case of a parasitic organism, the life cycle is described including the different host (s) that it deserves to survive and the different forms or morphologies that it can adopt, as well as its eating habits and the other behavioral characteristics that characterize it at each stage..

Importance

Image by Ewa Urban on www.pixabay.com

Since many parasites affect human health, parasitology is of great importance for the study of these, in order to know them better and determine the best way to treat the diseases that they cause.

Given that many farm animals can be seriously affected by multiple types of parasites (endo- and ectoparasites), causing great economic losses worldwide, parasitology is essential for both treatment and prevention and management of these.

References

Cook, GC (2001). History of parasitology (p. 1). Wiley.
Cox, FE (2002). History of human parasitology. Clinical microbiology reviews, 15 (4), 595-612.
Kochin, BF, Bull, JJ, & Antia, R. (2010). Parasite evolution and life history theory. PLoS biology, 8 (10).
Loker, E., & Hofkin, B. (2015). Parasitology: a conceptual approach. Garland Science.
Power, HJ (2001). History of Parasitology. e LS.
Schmidt, GD, Roberts, LS, & Janovy, J. (1977). Foundations of parasitology (pp. 604-604). Saint Louis: Mosby.
Solomon, EP, Berg, LR, & Martin, DW (2011). Biology (9th edn). Brooks / Cole, Cengage Learning: USA.

PARASITOLOGY: HISTORY, WHAT DOES IT STUDY ?, BRANCHES, CONCEPTS - BIOLOGY - 2025