Concept of Parasitology
Parasitology is the branch of biology that studies parasites, their characteristics (morphology, molecular, genetic and evolutionary), their way of life (reproduction, life cycle and relationship with the host) and diseases, or parasitic infections caused by them (epidemiology, geographic distribution, transmission and detection techniques and disposal). Parasitology is divided into vegetal parasitology and animal parasitology, which are the study of parasites and parasitic diseases of plants and animals, respectively. In turn, the animal parasitology is divided in human parasitology and veterinary parasitology.
In strict sense, parasitology is the study of protozoan parasites (e.g. Leismania sp.), helminths (e.g. ringworm Ascaris sp.) and arthropods (e.g. fleas). Thus, it includes three branches of zoology: protozoloogy, helminthology and arthropodology.
Parasites have a great diversity in morphology. Sizes can range from a few micrometers (Trypanosoma sp.) to more than a dozen meters (Taenia sp.). They can take different forms throughout their life cycle, be found inside or outside of the host cells (intracellular or free) and, in some cases, they can form cysts when conditions are not favourable.
Nomenclature and systematics of parasites have evolved a lot over the last few years; they are based now not only in morphology but also in genetic and immunological features.
Parasitology also deals with the study of the epidemiology of diseases caused by parasites. In this study, the following factors are important:
– The existence of a reservoir: sick human being or animal that carry the parasite (e.g. the Anopheles mosquito which transmits the etiologic agent of malaria, a protozoa of the genus Plasmodium);
– The presence of vector(s) (intermediate host(s));
– Geographical conditions (presence of the parasite and the host in the same territory, population density, etc.):
– Climatic conditions (Temperature, humidity, etc.);
– Ethological conditions (sociocultural behaviour, hygiene habits, economic conditions, etc.)
– Host resistance (conditioned by age, genetics, immunity, presence of other diseases, etc.).
References:
Gunn, A. & Pitt, S. J. (2012). Parasitology: An Integrated Approach. London: John Wiley & Sons.
Paniker, C.K. (2013). Paniker’s Textbook of Medical Parasitology. 7th ed. New Dehli: Jaypee Brother Medical Publishers.
Zeibig, E. (2014). Parasitologia Clínica: Uma abordagem clínico- laboratorial. 2nd ed. Rio de Janeiro: Elsevier.
