Parasitology Introduction PDF

Parasitology  Parasitology Parasitology is the science which deals with parasites. Medical Parasitology deals with those members of the animal kingdom that sometimes in their life cycle take up temporary or permanent abode in or upon a human host. ...

Parasitology  Parasitology Parasitology is the science which deals with parasites. Medical Parasitology deals with those members of the animal kingdom that sometimes in their life cycle take up temporary or permanent abode in or upon a human host.  Some basic definitions: ❖ Parasites: these are organisms which have adapted themselves to existence in (endoparasites) or on (ectoparasites) another organism (host ) to obtain food and shelter. ❖ Parasites medically important to humans can be divided into: a. Ectoparasites: Live on the surface of its host. b. Endoparasites: Live inside the body of the host, subdivided into: i. Obligate Parasites: Can’t live independently from the host i.e. permanent residence. ii. Temporary Parasites: It visits its host from time to time, spending only part of their life as parasites and another part as free-living organisms. iii. Facultative Parasites: Can live free far from the host or as parasite. c. Zoonotic Parasites: which are normally found in wild and/or domestic animals and may harm human.  Some basic definitions: ❖ Symbiosis: Parasitology is largely a study of symbiosis or living together. Usually the symbionts are of different species but not necessarily. ❖ Interactions of symbionts Phoresis: one symbiont or phoront is attached to another animal for transportation only, neither organism is helped or harmed. Mutualism: describes a relationship in which both mutuals benefit from the association. ❖Interactions of symbionts Commensalism: in it one partner (commensal) benefits from the association, but the host is neither helped nor harmed. Parasitism: a relationship in which, the parasite benefits while the host is harmed.  Types of Hosts: 1. Definitive host: is that host harboring the adult or sexually mature stage of the parasite. 2. Intermediate host: is that host in which the immature or larval stage of the parasite is found or in which the parasite multiplies asexually. 3. Reservoir host: is an animal harboring the parasite to ensure continuity of its life cycle and act as additional source and a store of infection. 4. Vector: is usually an arthropod host in which biological changes or multiplication of a parasite take place to carry that parasite to its specific host. 5. Paratenic host: is a transport host in which the parasite undergoes no development but remains alive and infective to other hosts.  Incidence of parasitic infections : Humans have suffered greatly through the centuries because of parasites. Millions of people particularly in tropics and subtropics are debilitated, disfigured, blinded and inconvenienced by such infections.Many are diseases of the poor, the lower socioeconomic groups, those in primitive surroundings and those in substandard living conditions. Nowadays immigration and travelling spread most parasitic infections worldwide.  Factors that influence the incidence of parasitic infections : These factors are related to such environmental factors as : climates, soil texture, availability of suitable definitive and intermediate hosts and vectors. The eating and sanitary habits of the population, the occupation and nutritional status, the barefoot people and the consumption of uncooked vegetables where humans excreta have been used as fertilizer.  Requirements for the survival of parasitic infections : The parasite must gain entrance into the host, survive and multiply there, eventually leave the host, and contact the appropriate intermediate host and vector.  Diagnosis of parasitic infections : Diagnosis based solely on clinical signs and symptoms is rarely possible without laboratory confirmation. The symptomatology of parasitic diseases is too diversified, too non specific to lead to accurate clinical diagnosis. 1. The microscope is extensively used in the laboratory identification of parasitic infections through fecal specimens, blood smears or tissue examination. 2. Serological tests are increasing for diseases that elicit an appreciable antibody response. 3. Molecular biological methods include DNA probes.  Control of parasitic infections: It begins with knowledge of the life cycles of the parasites. To overcome parasitic diseases requires efforts to improve the living conditions, lowering malnutrition , solve the problems of sanitation , control of water supply, sanitary disposal of sewage, control of arthropod vectors and inspection and sanitary packaging of foods. ❖Immunization: measures for immunization have not developed rapidly for the control of parasitic diseases. The parasites are antigenically very complex so that it is difficult to assess the immunological response of the host. ❖Chemotherapy: It is important to develop always new drugs since some of them have considerable toxicity and the appearance of drugs – resistant strains hinder progress in the treatment of a parasitic disease.  Medical Helminthology ❖Helminths (in Greeks helmins = worm) are macroscopic, multicelluar worms that have microscopic infective forms; eggs and encysted or free living lava(also known as metazoa). ❖It includes two phyla: 1. Phylum nemalthelminthes (Round worms or Nematodes). 2. phylum platyhelminthes (Flat worms) : a. Class cestoda (Tapeworms). b. Class trematoda (Flukes).