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The Parasites January 19th, 2010 Parasite biology • Eukaryotic cells – – – – Complex cell structure Nucleus Organelles Mitochondria or similar structures • Can be single celled or multicellular • Feed on bacteria and small nutrients Parasite biology • Complex life cycles • Distinct life stages that undergo structural changes • Some stages are reproductive • Only certain stages are infectious • Different stages take place in different places – Environment – Tissues of host – Tissues of vector (insect) Example: Malaria life cycle Example: Cryptosporidium life cycle Parasite Classification • The protozoa (protists) – Single celled eukaryotes • The helminths – Multicellular eukaryotes The Protozoa: Characteristics • Single celled organisms • Environmental stages inhabit water or soil • Most are aerobic • Consume food in several ways – – – – Transport across membrane Taking food into cellular openings Engulfing food Digest food using specialized structures inside cells (food vacuoles) The Protozoa: Structure Protozoa: life cycles • Different from organism to organism, but some common elements • Environmentally resistant life stages – The cyst • Reproductive stages – Sexual and asexual Protozoa: the cyst • Environmentally resistant life stage • Protective capsule forms around the cell • Allows survival outside a living host – transmission from host to host • Resistance to environmental stressors – Low moisture – Lack of nutrients – Lack of oxygen – Unsuitable temperatures Protozoa: Reproduction • Some have sexual reproductive stages – gametocytes • Asexual reproduction is common – Fission (like bacteria) – Budding – Schizogony Protozoan taxonomy • Protozoa are quite diverse • Divided into phyla • Currently done using ribosomal RNA sequencing • As with bacteria, this is changing as techniques advance and more organisms are sequenced Protozoan taxonomy: the phyla • Archaezoa • Microspora • Amoebozoa • Apicomplexa • Ciliophora • Euglenozoa Archaezoa • • • • Unique feature: lack mitochondria Many live in intestinal tracts of animals Flagellated Species of public health importance: Giardia lamblia Microspora • Unique feature: lack mitochondria • Intracellular parasites (live inside host cells) • Species of public health importance: Enterocytozoon bieneusi E. bieneusi cysts inside a eukaryotic cell E. bieneusi in stool smear Amoebozoa • The amoebas • Unique feature: use pseudopods for motility and to get food • Intestinal parasites • Species of public health importance: Entamoeba histolytica Cyst Trophozoite Apicomplexa • Unique feature: have organelles that release enzymes to aid in penetration of host tissues • Intracellular parasites (live inside host cells) • Complex life cycles with multiple hosts • Genus of public health importance: Plasmodium Ciliophora • Unique feature: cilia – Small “hairs” on the cell that propel the cell and move food toward it • Intestinal parasite • Genus of public health importance: Balantidium coli Cyst Trophozoite Euglenozoa • Unique feature: the hemoflagellates travel in the circulatory system of an infected host • Long, slender cells move by undulation • Genus of public health importance: Trypanosoma The Helminths The Helminths: Characteristics • The parasitic worms • Multicellular organisms • Digestive, circulatory, nervous, excretory, and reproductive systems • Spend part or all of their lives in humans • Invade and live in tissues The Helminths: life cycles • Complex life cycles • May have multiple hosts • Larval stages: developmental – Include eggs • Adult stages – Worms • Sexual reproduction The Helminths: life cycles Helminth taxonomy Two phyla: • Platyhelminthes (the flatworms) – Trematodes – Cestodes • Nematoda (the roundworms) Trematodes • • • • Also known as flukes Flat shaped body Attach to tissues via suckers Genus of public health importance: Schistosoma Cestodes • Also known as the tapeworms • Intestinal parasites – Lack a digestive system; absorb nutrients from their host – Attach to tissues via suckers • Genus of public health importance: Ehinococcus and Taenia Nematodes • Also known as the roundworms • Two types – Egg is infective – Larva is infective • Genus of public health importance – Ascaris – Necator (hookworm) – Trichinella Nematodes Ascaris Necator Trichinella Key Concepts • Eukaryotic cells • Can be single celled or multicellular • Feed on bacteria and small nutrients • Complex life cycles – Distinct life stages that undergo structural changes – Some stages are reproductive – Different stages take place in different places Key Concepts • The protozoa (protists) – – – – Single celled eukaryotes Environmental stages inhabit water or soil Most are aerobic Consume food in several ways • The helminths – – – – Multicellular eukaryotes The parasitic worms Multicellular organisms Digestive, circulatory, nervous, excretory, and reproductive systems – Spend part or all of their lives in humans – Invade and live in tissues Key Concepts The protozoa: • Archaezoa • Microspora • Amoebozoa • Apicomplexa • Ciliophora • Euglenozoa The helminths: • Platyhelminthes (the flatworms) – Trematodes – Cestodes • Nematoda (the roundworms)
