parasitology

The scientific study of parasites and of parasitism. Parasitism is a subdivision of symbiosis and is defined as an intimate association between an organism (parasite) and another, larger species of organism (host) upon which the parasite is metabolically dependent. Implicit in this definition is the concept that the host is harmed, while the parasite benefits from the association. Although technically parasites, pathogenic bacteria and viruses and nematode, fungal, and insect parasites of plants are traditionally outside the field of parasitology.

Parasites often cause important diseases of humans and animals. For this reason, parasitology is an active field of study; advances in biotechnology have raised expectations for the development of new drugs, vaccines, and other control measures. However, these expectations are dampened by the inherent complexity of parasites and host-parasite relationships, the entrenchment of parasites and vectors in their environments, and the vast socioeconomic problems in the geographical areas where parasites are most prevalent.

The ecological and physiological relationships between parasites and their hosts constitute some of the most impressive examples of biological adaptation known. Much of classical parasitology has been devoted to the elucidation of one of the most important aspects of host-parasite ecological relationships, namely, the dispersion and the transmission of parasites to new hosts.

Parasite life cycles range from simple to highly complex. Simple life cycles (transmission from animal to animal) are direct and horizontal with adaptations that include high reproduction rates, and the production of relatively inactive stages (cysts or eggs) that are resistant to environmental factors such as desiccation, ultraviolet radiation, and extreme temperatures. The infective stages are passively consumed when food or water is contaminated with feces that contain cysts. The cysts are then activated in the gut by cues such as acidity to continue their development. Other direct-transmission parasites, such as hookworms, actively invade new hosts by penetrating the skin. Physiologically more complicated are those life cycles that are direct and vertical, with transmission being from mother to offspring. The main adaptation of the parasite for this type of life cycle is the ability to gain access to the fetus or young animal through the ovaries, placenta, or mammary glands of the mother.

Many parasites have taken advantage of the food chain of free-living animals for transmission to new hosts. During their life cycle, these parasites have intermediate hosts that are the normal prey of their final hosts. Parasites may ascend the food chain by utilizing a succession of progressively larger hosts, a process called paratenesis. See also Food web.

Vectors are intermediate hosts that are not eaten by the final host, but rather serve as factories for the production of more parasites and may even carry them to new hosts or to new environments frequented by potential hosts. Blood-sucking athropods such as mosquitoes and tsetse flies are well-known examples. After acquiring the parasite from an infected host, they move to another host, which they bite and infect. Snails are important vectors for two-host trematodes (flukes), which increase their numbers greatly in the snail by asexual reproduction. The stages that leave the snail may either infect second intermediate hosts that are eaten by carnivorous final hosts, may encyst on vegetation that is eaten by herbivorous hosts, or in the case of the blood flukes (schistosomes) may swim to and directly penetrate the final host.

Metabolic dependency is the key to parasitism, and parasites employ many ways to feed off their hosts. The simplest is exhibited by the common intestinal roundworm, Ascaris, which consumes the host's intestinal contents. Parasites require from their hosts not only energy-yielding molecules but also basic monomers for macromolecular synthesis and essential cofactors for these synthetic processes. Many examples of the specific absence of key parts of energy-yielding or biosynthetic pathways in parasites are known, and these missing enzymes, cofactors, or intermediates are supplied by the host. Tapeworms are more complex than Ascaris in nutritional requirements from the host. They lack a gut, but their surface actively takes up, by facilitated diffusion or active transport, small molecules such as amino acids and simple sugars.

Parasites, by coevolving with their hosts, have the ability to evade the immune response. The best-known evasive tactic is antigenic variation, as found in African trypanosomes, which have a complicated genetic mechanism for producing alternative forms of a glycoprotein that virtually cover the entire parasite. By going through a genetically programmed sequence of variant surface glycoproteins, the trypanosome population in a host stays one step ahead of immunity and is not eliminated. Other possible immune escape mechanisms in parasites have been discovered and probably cooperate to prolong parasite survival.

Parasites are not altogether exempt from the effects of immunity. Rather than completely eliminating parasites, the immune system more often functions to control their populations in the host. Thus a balance is achieved between hosts and parasites that have lived in long evolutionary association, with both surviving through compromise. Enhancing these particular antiparasite mechanisms and neutralizing the parasite's evasion mechanisms would tip the balance in favor of the host. See also Medical parasitology; Population ecology.

A person skilled in parasitology.

Adult black fly (Simulium yahense) with (Onchocerca volvulus) emerging from the insect's antenna. The parasite is responsible for the disease known as River Blindness in Africa. Sample was chemically fixed and critical point dried, then observed using conventional scanning electron microscopy. Magnified 100X.

Parasitology is the study of parasites, their hosts, and the relationship between them. As a biological discipline, the scope of parasitology is not determined by the organism or environment in question, but by their way of life. This means it forms a synthesis of other disciplines, and draws on techniques from fields such as cell biology, bioinformatics, biochemistry, molecular biology, immunology, genetics, evolution and ecology.

Contents 1 Fields 1.1 Medical parasitology 1.2 Veterinary parasitology 1.3 Quantitative parasitology 1.4 Structural parasitology 1.5 Parasite ecology 1.6 Taxonomy and phylogenetics 2 See also 3 External links

Fields

The study of these diverse organisms means that the subject is often broken up into simpler, more focused units, which use common techniques, even if they are not studying the same organisms or diseases. Much research in parasitology falls somewhere between two or more of these definitions. In general, the study of prokaryotes fall under the field of bacteriology rather than parasitology.

Medical parasitology

One of the largest fields in parasitology, medical parasitology is the study of those parasites which infect humans. These include organisms such as:

• Plasmodium spp., the protozoan parasite which causes malaria. The four species of malaria parasites infective to humans are Plasmodium falciparum,Plasmodium malariae, Plasmodium vivax & Plasmodium ovale.
• Leishmania donovani, the unicellular organism which causes leishmaniasis
• multicellular organisms such as Schistosoma spp., Wuchereria bancrofti and Necator americanus

Medical parasitology can involve drug development, epidemiological studies and study of zoonoses.

Veterinary parasitology

Main article: Veterinary parasitology

The study of parasites that cause economic losses in agriculture or aquaculture operations, or which infect companion animals. Examples of species studied are:

• Lucilia sericata, a blowfly, which lays eggs on the skins of farm animals. The maggots hatch and burrow into the flesh, distressing the animal and causing economic loss to the farmer
• Otodectes cynotis, the cat ear mite, responsible for Canker.
• Gyrodactylus salaris, a monogenean parasite of salmon, which can wipe out populations which are not resistant.

Quantitative parasitology

Main article: Quantitative parasitology

Parasites exhibit an aggregated distribution among host individuals, thus the majority of parasites live in the minority of hosts. This feature forces parasitologists to use advanced biostatistical methodologies.

Structural parasitology

Main article: Structural parasitology

This is the study of structures of proteins from parasites. Determination of parasitic protein structures may help to better understand how these proteins function differently from homologous proteins in humans. In addition, protein structures may inform the process of drug discovery.

Parasite ecology

Parasites can provide information about host population ecology. In fisheries biology, for example, parasite communities can be used to distinguish distinct populations of the same fish species co-inhabiting a region. Additionally, parasites possess a variety of specialized traits and life-history strategies that enable them to colonize hosts. Understanding these aspects of parasite ecology, of interest in their own right, can illuminate parasite-avoidance strategies employed by hosts

Taxonomy and phylogenetics

The huge diversity between parasitic organisms creates a challenge for biologists who wish to describe and catalogue them. Recent developments in using DNA to identify separate species and to investigate the relationship between groups at various taxonomic scales has been enormously useful to parasitologists, as many parasites are highly degenerate, disguising relationships between species.

See also

• [Parasitism knol[1]
• [Marine parasites of man[2]

• Important publications in parasitology
• Parasitologists
• [World Parasitologists]

• [Parasitology Societies,Associations and Federation]

• [Parasitology Glossary]

• [Parasitology Links ]

External links

• All about Parasites
• Online lectures in parasitology University of South Carolina
• American Society of Parasitologists
• ARC-NHMRC Research Network for Parasitology
• Australian Society for Parasitology
• British Society for Parasitology
• Chinese Society of Parasitology
• Czech Society for Parasitology
• European Scientific Counsel Companion Animal Parasites
• Hungarian Society of Parasitologists
• Indian Society of Parasitology
• Israel Society for Parasitology, Protozoology and Tropical Diseases
• Japanese Society of Parasitology
• Korean Society for Parasitology
• Nederlandse Vereniging voor Parasitologie
• New Zealand Society for Parasitology
• Scandinavian and Baltic Societies for Parasitology
• Department of Parasitology, Cluj-Napoca, Romania

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Dansk (Danish)
n. - parasitologi

Nederlands (Dutch)
parasitologie

Français (French)
n. - parasitologie

Deutsch (German)
n. - Parasitologie

Ελληνική (Greek)
n. - παρασιτολογία

Italiano (Italian)
parassitologia

Português (Portuguese)
n. - parasitologia (f)

Русский (Russian)
паразитология

Español (Spanish)
n. - parasitología

Svenska (Swedish)
n. - parasitologi

中文（简体）(Chinese (Simplified))
寄生虫学

中文（繁體）(Chinese (Traditional))
n. - 寄生蟲學

한국어 (Korean)
n. - 기생충학

日本語 (Japanese)
n. - 寄生虫学

العربيه (Arabic)
‏(الاسم) علم الطفيليات‏

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n. - ‮חקר הטפילים (בטבע)‬

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