PARASITOLOGY LECTURE PDF - General Concepts & Host-Parasite Interactions

Medical Parasitology LECTURE (1) General Concepts of Medical Parasitology 1  Medical Parasitology Medical  The science that deals with the study of parasites...

Medical Parasitology LECTURE (1) General Concepts of Medical Parasitology 1  Medical Parasitology Medical  The science that deals with the study of parasites that infects the Parasitology human and the diseases they produce.  An organism that lives in or on another organism (its host) and Parasite benefits by deriving nutrients and protection at the other's expense. Host  The organism in or on which a parasite lives.  These are parasites that live only in or on their hosts. Obligatory ❶  They can’t complete their life-cycle without a suitable host. parasites  As schistosoma.  These parasites can live freely in environment (in soil or water) Facultative ❷  also live as parasites in hosts under unfavorable parasites environmental conditions. ❸ Ectoparasites  Parasites which live on the outside of the host. ❹ Endoparasites  Parasites which live within the body of the host. Temporary  The parasite visits the host temporarily from time to time for ❺ parasites feeding as mosquito. Permanent  These are parasites which always infect the host and don’t ❻ parasites leave him. Specific ❼  The parasite affects only one host species. parasites  These are free living organisms which enter the human body by Accidental mistake ❽ parasites  e.g. larvae of flies which are accidentally ingested and live in the intestine of man.  Parasitic species foreign to the host which has just passed Coprozoic through alimentary canal without infecting the host to be ❾ (Spurious) recovered in feces. parasites  Example: parasite eggs in animal liver. 2  Medical Parasitology Obligatory parasites Facultative parasites Ectoparasites Endoparasites Temporary parasites Permanent parasites 3  Medical Parasitology Specific parasites Coprozoic (Spurious) parasites 4  Medical Parasitology Definitive  A host in which the parasite reaches its sexual maturity (adult ❶ host stage). Intermediate  A host in which the immature (larval not adult) stage of ❷ host parasite is found, or in which the parasite multiplies asexually. Reservoir  An animal that harbors the parasite. ❸ host  Acts as continuous source of human infection. Paratenic  A host that harbors a parasite in arrested state of development ❹ (transport but the parasite remains alive and viable, ready to infect a host) subsequent suitable host. Dead-end  A host from which infectious agents are not transmitted to ❺ host other susceptible hosts.  An arthropod host that transmits the parasite from one host to ❻ Vector another and has a role in its life cycle. Fasciola definitive, reservoir and The parasitic stage settles without intermediate hosts further development in paratenic host 5  Medical Parasitology The dead-end host doesn’t allow parasite Leishmania life cycle transmission Anopheles is the vector responsible for transmission of malaria 6  Medical Parasitology  Relationship between two organisms that live closely together.  One of the two organisms (parasite) benefits, as it gains ❶ Parasitism protection and nutrition on the expense of the other (host) that suffers from such association.  Both organisms live together and the commensal organism benefits without causing harm to the other. ❷ Commensalism  Both organisms benefit from the association to an extent that both can’t live separate (a flagellate in the intestine of termite that feed on wood). ❸ Mutualism  The phoront is usually smaller organism and is mechanically carried by the other which is usually large.  In phoresis there is no dependency but just carriage (dientamoeba fragilis on enterobius egg). ❹ Phoresis 7  Medical Parasitology a. Direct contact with infested person e.g. scabies, lice. Contact b. Indirect contact with infected person’s towels, bed sheets or ❶ transmission other personal items e.g. scabies. c. Sexual contact e.g. Trichomonas vaginalis. a. Eating or drinking contaminated water or food e.g. helminthes ova Food and ❷ b. Eating raw or under-cooked or under-salted fish e.g. drink Heterophyes heterophyes. c. Eating raw or under-cooked meat e.g. Taenia saginata (in cattle meat). By a. Mechanically e.g. housefly transmit helminthes ova. ❸ arthropods b. Biologically by bite of blood sucking insects e.g. malaria. Blood ❹  With contaminated syringes e.g. malaria. transfusion Trans- ❺ placental  e.g. Toxoplasma gondii. transmission 8  Medical Parasitology Lytic necrosis Trauma Physical obstruction Inflammatory reaction  Enzymes produced by  Attachment of some  Masses of collected  Clinical illness may occur some parasites cause parasites in their habitat worms may cause due to inflammatory Definition lysis of tissue in their causes tear and damage obstruction to luminal changes and consequent habitat. to the tissue. organs. fibrosis.  Ascaris lumbricoides  Entamoeba histolytica  Hookworm causing  Schistosoma mansoni Example causing intestinal causing intestinal ulcers. bleeding and anemia. causing liver fibrosis. obstruction. Allergic manifestation Neoplasia Space occupying lesions  The host immune response to the  Few parasitic infections lead to  Some parasites cause cystic lesions Definition parasite may cause allergic malignancy. that compress on surroundings. manifestations.  Schistosoma haematobium  Echinococcus granulosus causing Example  insect bites causing allergic rash. causing cancer bladder. hydatid cyst in liver. 9  Medical Parasitology  Includes the study of three major groups of animals: 1. Parasitic helminths (worms). 2. Parasitic protozoa. 3. Arthropods that directly cause disease or act as vectors of various pathogens. 10