Parasitology is a biological discipline that is concerned with parasites; the study of parasitic organism, their hosts and the relationship between them. Studies involve the parasite’s morphology/ characteristics, genetic evolutionary, way of life (life cycle and relationship with host, reproduction) and parasitic infections and diseases.
The study of parasitism is multidisciplinary subject covering many topics including: morphology, taxonomy, behavior, pathogenesis genetics, biochemistry, cell biology, bioinformatics, developmental biology, ecology as well as the diagnosis, immunology and treatment of infections.
Parasitology also deals with the study of the epidemiology of diseases caused by parasites. This scope covers the vectors, hosts, climate conditions, economic conditions, geographical conditions; ethological conditions (hygiene habits, socio-cultural conditions) host resistance (conditioned by genetics, age, immunity)
Traditionally parasitology is the study of protozoan parasites (e.g. Leismania sp), helminthes ( Ascaris sp) and arthropods (e.g. fleas)
Protozoan are unicellular eukaryotic organisms (with a membrane-bound nucleus) which exist as structurally and functionally independent individual cells (including those species which form colonies) Protozoa can either be free living or parasitic. They are able to multiply in humans, which contributes to their survival and also permits serious infections to develop from just a single organism. Transmission of protozoa that live in a human’s intestine to another human typically occurs through a fecal-oral route. Protozoa that live in the blood or tissue of humans are transmitted to other humans by an arthropod vector (for example, through the bite of a mosquito or sand fly).
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Balantidium coli trophozoite
(Images from CDC)
Helminths are large, multicellular organisms that are generally visible to the naked eye in their adult stages. Like protozoa, helminths can be either free-living or parasitic in nature. They are commonly known as worm parasites. The general name of the infectious disease caused by helminths is helminthiasis. The majority of the helminths live in the intestine and are therefore often called intestinal worms. In their adult form, helminths cannot multiply in humans.
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Eggs of helminths
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Arthropods are invertebrates with segmented bodies and jointed limbs. They are involved in nearly every kind of parasitic relationship, either as parasites themselves or as hosts/vectors for other parasitic microorganisms. They are generally ectoparasitic on, or in, the skin of vertebrate hosts. Many species are haematophagous (suck blood) while others are histophagous (tissue-feeders) and bite or burrow in dermal tissues causing trauma, inflammation and hypersensitivity reactions. Most parasitic arthropods belong to 2 main classes: the 6-legged insects, and the 8-legged arachnids. Infestations are transmitted from host-to-host either by direct contact or by free-living larvae or adults actively seeking hosts.
(Image from ecolab.com) (Images from medical news today)
Protozoology, helminthology and arthropodology are key zoological branches in this discipline.
Branches of parasitology are:-
1) Medical - Involves parasites that infect humans and the medical significance of host. It is concerned with the parasitic diseases, clinical picture and the human response generated against them. Moreover the various diagnosis methods, treatment, prevention, and control.
2)Veterinary- the study of animal parasites, especially relationships between parasites and animal hosts. Parasites of domestic animals, (livestock and pet animals), as well as wildlife animals, are considered. The key aim of veterinary parasitology is to protect animals and improve their health as these parasites cause economic losses in agriculture or aquaculture operations, or which infect companion animals.
3) Quantitative- the quantitative study of parasitism in a host population involves the use of statistics to draw meaningful conclusions from observations of the prevalence and intensity of parasitic infection Quantifying parasites in a sample of hosts or comparing measures of infection across two or more samples can be challenging. The parasitic infection of a sample of hosts mostly exhibits a complex pattern that cannot be adequately quantified by a single statistical measure. Parasitologists use advanced biostatistical methodologies.
4) Structural- Study of the structure of parasitic proteins; this gives a better understanding of how parasitic proteins function differently from homologous proteins from a human. This helps in distinguishing of functional pathways in these organisms in comparison to humans. Protein structure may contribute to the process of drug discovery.
5) Parasite ecology- Involves study of the ecology of parasites i.e. interactions between parasites, host and the environment.
6) Conservation Biology of parasites- Aims to maintain parasite biodiversity concerned with the protection and preservation of vulnerable species. A large proportion of parasite species are threatened by extinction, partly due to efforts to eradicate parasites which infect humans or domestic animals, or damage the human economy, but also caused by the decline or fragmentation of host populations and the extinction of host species. Parasites act as vital trophic regulators.
Parasitology is a dynamic field as the relationship between the parasite and hosts are constantly changing. Parasites have multi-life stages, different immune stages, it is difficult to formulate vaccine and also difficult to control.