Principle and Concept of Parasitology PDF

 Parasite: an organism that lives at the expense(deriving something and causing harm as it’s deriving it) of another organism (host) Parasites that cause disease are called pathogens Parasitology is the branch of science that deals with the study of parasites and parasitism(the interacti...

 Parasite: an organism that lives at the expense(deriving something and causing harm as it’s deriving it) of another organism (host) Parasites that cause disease are called pathogens Parasitology is the branch of science that deals with the study of parasites and parasitism(the interaction between the parasite and host)  Historically, in the development of the science of biology, parasitology came to refer to the study of protozoa, helminths, and arthropods that live at the expense of other organisms  A parasite is a living organism which must spend at least a part of its life cycle on another living organism (the host). This means that a parasite is an organism which is metabolically dependent on another organism for its survival. Attributes of a parasite Always smaller than the host Must not necessarily kill the host Require host molecules or physiological process for survival May or may not cause disease (pathogenic) Parasitism Parasites in Relation to Their Hosts Ectoparasites live on the surface of other organisms (e.g. ticks and lice) Endoparasites live within the bodies of other organisms (e.g. protozoa and worms) Most parasites are either obligate parasites: must spend at least some of their life cycle in or on a host facultative parasites: normally are free-living, but can obtain nutrients from a host  Parasites are also categorized according to the duration of their association with their hosts: Permanent parasites (tapeworms): remain in or on a host once they have invaded it Temporary parasites (biting insects): feed on and then leave their hosts Accidental parasites (ticks): invade an organism other than their normal host Hyperparasitism (malaria): refers to a parasite itself having parasites  Vector: agents of transmission, of many human parasitic diseases A vector is an organism that does not cause disease itself but which spreads infection by conveying pathogens from one host to another. Species of mosquito, for example, serve as vectors for the deadly disease Malaria An organism that transfers a parasite to a new host is a vector/ a carrier of a disease causing agent  Biological vector: A vector in which the parasite/pathogen goes through part of its life cycle (malaria mosquito is both a host and a biological vector) Mechanical vector: A vector that simply conveys pathogens to a susceptible individual and is not essential to the development of the organism. A vector in which the parasite/pathogen does not go through any part of its life cycle during transit (flies that carry parasite eggs, bacteria, or viruses from feces to food)  Definitive hosts: harbor a parasite while it reproduces sexually Intermediate hosts: harbor the parasite during some other developmental stages Examples: Mosquito is the definitive host for the malaria parasite because that parasite reproduces sexually in the mosquito; the human is an intermediate host  Reservoir hosts are infected organisms that make parasites available for transmission to other hosts  Many parasites have one or more mechanisms for evading host defense mechanisms: Host defense evasion Encystment Changing the parasite’s surface antigens Causing the host’s immune system to make antibodies that cannot react with the parasite’s antigens Invading host cells, where the parasites are out of reach of host defense mechanisms  Protozoa Animal-Like Protists (protozoa) Heterotrophic, mostly unicellular organisms (single- celled). Most are free living and some are commensals (live in or on other organisms without harming them)  Multiply in human host. Mastigophorans have flagella, few are free- living, but most live in symbiotic relationships. E.g. Giardia lamblia, Trypanosoma species, Leishmania species, Trichomonas vaginalis.  Sarcodines are usually amoeboid and move by means of pseudopodia. A few have flagella at some stages. E.g. Enthamoeba histolytica, Acanthamoeba species, Naegleria species. Apicomplexans are parasitic and immobile. They are intracellular parasites that reproduce asexually by a process called schizogony and sexually by sporogony. E.g. blood& tissue: Plasmodium species, Toxoplasma gondii Intestinal: Isospora belli, Cryptosoridium parvum, Cyclospora cayetanensis. Ciliates Largest group of protozoans Have cilia over most of their surfaces for movement and assist in food gathering Balantidium coli is the only ciliate that parasitizes humans and causes dysentery Have several highly specialized structures Contractile vacuole which regulates fluids Trichocysts tentacles used to capture prey Conjugation structure for genetic exchange Helminths Helminths, or worms, are bilaterally symmetrical They have left and right halves that are mirror images Also has a head and tail end Tissues are differentiated into three distinct layers: Ectoderm Mesoderm Endoderm  Helminths that parasitize humans include flatworms and roundworms Flatworms (Platyhelminthes)(Cestoda-tape worm, Trematoda-flukes, Monogenea) are primitive worms which lack a coelom and have a simple digestive tract with a single opening. Most flatworms are hermaphroditic. Roundworms (nematodes) share many characteristics with flatworms, but they have a pseudocoelom. They have cylindrical bodies with tapered ends and are covered with a thick, protective cuticle  Parasitic Helminths  Flukes E.g. blood flukes: Schistosoma species Intestinal fluke: Fasciolopsis buski Tissue flukes; Liver flukes: Fasciola hepatica, Opistorchis (clonorchis sinensis) Lung fluke: Paragonimus westamania  Tapeworms E.g. Teania species, Echinococcus granulosus, Diphyllobothrium latum  Roundworms Adult roundworms of the intestine. E.g. Ascaris lumbricoides, Strongyloides stercoralis Enterobius vermicularis (threadworm), Trichuris trichiura(whipworm) Hookworms; E.g. Ancylostoma duodenale, Necator americanus  Tissue& filarial Nematodes Wuchereria bancrofti, Brugia species, Loaloa, Onchocerca volvulus, Dracunculus medinensis(guineaworm), Trichinella species  Parasitic flukes have a complex life cycle often involving several hosts Miracidia: free-swimming forms Sporocysts: life form after penetration of molluscan hosts and divide to form rediae Rediae give rise to free-swimming cercariae which penetrate another arthropod host to encyst as metacercariae Tapeworms Consist of a scolex, or head end with suckers that attach to the intestinal wall and a long chain of hermaphroditic proglottids Proglottids: body components that contain mainly reproductive organs of both sexes  The life cycle of tapeworms usually includes the following stages: Embryos develop inside eggs and are released from proglottids Proglottids and eggs leave the host’s body with the feces Another animal ingests vegetation or water contaminated with eggs and eggs hatch into larvae, which invade the intestinal wall A larvae can develop into a cysticercus (bladder worm), or it can form a cyst A cyst can enlarge and develop many tapeworm heads within it (hydatid cyst) and if an animal eats flesh containing this, each scolex can develop into a new tapeworm  Adult Roundworms Most roundworms that parasitize humans live much of their life cycle in the digestive tract Usually enter the body by ingestion with food or water, but some penetrate the skin (e.g. hookworm) The life cycles of intestinal roundworms show considerable variation Arthropods Constitute the largest group of living organisms 80% of all animal species belong to phylum Arthropoda Characterized by: Jointed chitinous exoskeletons Segmented bodies Jointed appendages Have a true coelom Small brain and an extensive network of nerves Sexes are distinct and females lay many eggs  Classification of Arthropods (ectoparasites). Certain members of three subgroups (classes) of arthropods are important either as parasites or as disease vectors. Arachnids e.g?? Insects e.g ?? Crustaceans e.g ??  Insects Have three body regions :Head,Thorax,Abdomen Three pairs of legs Highly specialized mouth parts Crustaceans Generally aquatic arthropods Typically have a pair of appendages associated with each segment Appendages include: Mouthparts, Claws, Walking legs, Appendages that aid in swimming or copulation