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Some useful Definitions Symbiosis It was originally coined to refer to all cases where dissimilar organisms or species (e.g. heterogenetic associations) live together in an close association. Major categories of Symbiosis Phoresis Commensalism Mutualism Parasitism If we consider the degree of the association, then phoresis and commensalism represent “loose” associations, whereas mutualism and parasitism indicate “intimate” associations. Phoresis (Phoresy) Phoresis= migration; it can mean “to carry.” A type of symbiotic relationship in which one organism (the smaller phoront) is mechanically carried on or in another species (host). ‘The often overlooked form of symbiosis!’ Phoresis Phoresis Carrion beetle with mites Commensalism Commensalism derives from the English word commensal, meaning "sharing of food" in human social interaction, which in turn derives from the Latin “cum mensa”, meaning "sharing a table“. Commensalism occurs when one member of the associating pair, usually the smaller, receives all the benefit and the other member neither benefits nor is harmed. Commensalism • An orchid plant will attach itself high up a tree trunk to have a safe, sheltered place to grow and receive water dripping down the tree trunk. • The tree trunk which provides the habitat for the orchid seems to neither be harmed nor benefit from the relationship. Mutualism • Occurs when each member of the association benefits the other. • Mutuals are metabolically dependent on one another •This dependence can be facultative or obligated, in the latter case one organism cannot survive in the absence of the other. Mutualism Mutualism (facultative) Mutualism (facultative) The relationship between hermit crab and seaanemone is an excellent example of mutualism. Hermit crab lives inside empty shell of mollusk. The sea-anemone inhabits the outer surface of shell. Sea-anemone is transported from place to place to get food by crab. The Sea-anemone also gets food captured by crab. The stinging cells of sea-anemone protect the hermit crab from enemies. Thus, both partners are benefited. Mutualism (obligate) Wolbachia and filarial nematodes Wolbachia are common intracellular bacteria that are found in arthropods and nematodes. Outside of insects, Wolbachia infects a variety of isopod species, spiders, mites, and many species of filarial nematodes (a type of parasitic worm), including those causing onchocerciasis ("River Blindness") and elephantiasis in humans as well as heartworms in dogs. Mutualism (obligate) Wolbachia and filarial nematodes elephantiasis onchocerciasis ("River Blindness") heartworms in dogs Mutualism (obligate) Wolbachia within filarial nematodes are largely mutualistic, with Wolbachia being essential for host survival. Wolbachia (stained red) distributed throughout the lateral hypodermal cord cells and embryos within the uterus of nematode (Onchocerca volvulus). Cross section of adult female nematode (Brugia malayi) stained with antibody to Wolbachia surface protein (WSP). Wolbachia (red) are present in the lateral cords (LC) and ovaries (O) Mutualism (obligate) Applications to human health Not only are these disease-causing filarial worms infected with Wolbachia, but Wolbachia seem to play an inordinate role in these diseases. A large part of the pathogenicity of filarial nematodes is due to host immune response toward their Wolbachia. Elimination of Wolbachia from filarial nematodes generally results in either death or sterility of the nematode. Consequently, current strategies for control of filarial nematode diseases include elimination of Wolbachia via the simple doxycycline antibiotic rather than far more toxic anti-nematode medications. Parasitism Parasitos (para: beside; sitos: grain or food) A symbiotic relationship in which one organism (the parasite) benefits and the other (the host) is generally harmed. Parasites derive nutrition from their host and may also gain other benefits such as shelter and a habitat in which to grow and reproduce. Overlapping Now let’s focus on Parasitology Some useful definitions in Parasitology Parasitism Definitions of parasitism have traditionally focused upon some ecological aspect of the parasite-host interaction. Here, I will pinpoint the aspect concerning the metabolic dependency in the parasitological relationships. Metabolic Dependency • Parasites can be considered organisms which find their nourishment and habitat on other living organisms (belonging to a different species) without destroying it (the host). • Parasitism is an intimate relationship between two organisms during which time one organism (the parasite) is metabolically dependent on the host: Developmental Stimuli Nutritional Dependence Digestive Enzymes Control of Maturation Ecological relationship Some researchers have stressed that parasites are distinguished from free living organisms by their habitat preference. The habitat (=environment) is formed by another living animal to which the parasite transferred “the burden of regulating its relationship with the external environment”! Pathogenic Effects Some parasitologists emphasized that parasites produced harmful effects on their hosts Parasitism is defined as the form of symbiosis in which “one species lived at the expense of the other” in the association. I prefer another definition…. Webster’s Dictionary “An organism living ‘in’ or ‘on’ another living organism, obtaining from it part or all of its organic nutriment, commonly exhibiting some degree of adaptive structural modification, and causing some degree of real damage to its host” An unambiguous definition? •A number of parasitologists have concluded that there is no distinct ecology, function, evolution, or physiology that distinguishes all parasites from all non-parasites. •In essence, there is no such thing as an unambiguous definition of parasitism because only common ancestry is unambiguous in biology, and parasites do not represent a monophyletic group. An unambiguous definition? Parasitism is not a definition but a condition!!! Medical Parasitology Parasitic diseases Parasites Prevention Transmission Treatment Diagnosis Pathogenesis Life Cycle Morphology Conceptions related to medical parasitology Symbiosis Parasite (stages and mechanisms of interaction with the host and the environment) Life cycle Host (vector, reservoir, intermediate host, definitive host) Type of parasites Protozoa Nematodes Parasites Helminths Trematodes Cestodes Arthropods Ecto-parasites Endo-parasites Endoparasite and ectoparasite A parasite which lives in or on the body of the host is called endo-parasite (protozoa and helminthes) or ecto-parasite (arthropods). Host and type of host The host is an organism that harbors the parasite (usually larger than the parasite). Intermediate host: The host harboring the larvae or asexual stage of parasite. Final (definitive) host: The host harboring adult or sexual stage of parasite. Reservoir host: Animals harboring the same species of parasites as man (potential sources of human infection). Life cycle and type of life cycle Life cycle: The whole process of parasite growing and developing. Direct life-cycle: Only one host (no intermediate host). Indirect life cycle: Life cycle with more than one host (intermediate host and final host). Relationship (Effect) between parasite and host Parasites injures to host Host (animal or human) harbours parasite the host’s immune response produces: • Effects of the parasite on the host • Effects of the host on the parasite Effects of parasites on the host • Depriving the host of essential substance Hookworm Suck blood Anemia • Mechanical effects of parasites on the host Ascaris Perforation/Obstruction • Toxic and allergy effect (Hypersensitivity) e.g. Proteolytic enzyme/Necrosis e.g. Parasite antigen (anaphylaxix) Effects of the host on the parasites The host can produce certain degree resistance to parasites infection. The resistance (Immunity) is not very strong. In general, It doesn’t wipe out parasites completely, but may limit the number of parasites and establish balance with parasites. • Innate immunity • Acquired immunity (cellular and humoral: antibodies) Innate immunity Barrier: Prevent parasites to invade in certain degree. Skin/Mucous Membranes/Placenta. Acidity in skin or stomach can cause damage of the parasites. Phagocytosis: Non-specific/effective against a wide range of parasitic infection Acquired immunity Mechanism: Cellular and humoral immunity. Sterilizing immunity: Wipe out the parasites completely, meanwhile get a long-term specific resistance to re-infection. Rare! Non-sterilizing immunity: Wipe out most of the parasites, but not completely. Common! The basic factor of transmission of parasitic diseases Parasitic diseases Infectious diseases Transmission • The source of the infection • The routes of transmission • The susceptible host The combined effect of those factors determines the prevalence of the parasites at a given time and place and regulate the incidence of the parasitic diseases in certain local population. The source of the infection Patient: Persons who have parasites in their body and show clinical symptoms. Carrier: Persons who have parasites in their body and do not show symptoms. Reservoir host: Animals that harbor the same species of parasites as man. Sometimes, the parasites in animals can transmit into human. The routes of transmission I Congenital transmission: From mother to infant (Toxoplasmosis) Contact transmission: Direct contact (Trichomonas vaginalis) Indirect contact (Ascaris lumbricodes) Food transmission: Food contaminated with the infectious stage of parasites/The meat of the intermediate hosts containing infectious stage of parasites. The routes of transmission II Water transmission: Drink or contact the water contaminated the infectious stage of parasites. Soil transmission: Contamination of the soil by feces containing the certain stage of parasites and this stage can develop into host. Arthropod transmission: Vectors of certain parasitic diseases. The paths of invasion Digestive tract: Most common path of entrance (Food/Water transmission) Skin: Infective larvae perforate skin and reach to body and establish infection (soil/water transmission) Blood: Bloodsucking insects containing infective parasites bite the skin and inject parasites into human blood (arthropod transmission, i.e. malaria). The prevention measures of the parasitic diseases Controlling the source of the infection. Treatment of the patients, carriers and reservoir hosts. Intervention at the routes of transmission. Managing feces and water resource Controlling or eliminating vectors and intermediate hosts Protecting the susceptible hosts. Paying attention to personal hygiene, changing bad eating habit, taking medicine.