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Explore the fascinating world of parasitic worms and viruses, including their life cycles, anatomy, and how they cause diseases. Learn about flatworms, flukes, tapeworms, roundworms, and more. Discover the structure and replication process of viruses.
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Parasitic Worms • Kingdom Animalia: eukaryotic, no cell walls, heterotrophic nutrition, specialized tissues
A. Platyhelminthes • Flatworms • e.g. planarians
Platyhelminthes • Trematoda = flukes • leaf-shaped • parasitic • complex life cycles with several larval forms • larva = an immature form of an animal; does not look like the adult • ______________: where the larva lives • ______________: where the adult worm lives
Fluke anatomy • _________________ =having both functional ovaries andtestes
Schistosoma:blood flukes,male and female (in groove on males body) ____________________
Schistosomahaematobium • portal of entry: skin (Cercariae Larva) • source of infection: larvae from fresh water snails • disease is not contracted in U.S.A.(we don’t have host snail here), but more than 400,000 immigrants to this country have it ( + 200 million people in Asia, Africa, S. America & the Caribbean) • lives primarily in the pelvic veins • See Chapter 23 ( page 666-667), figure 23.27 • Monsters inside me….check it out!!!!: http://animal.discovery.com/videos/monsters-inside-me/
Platyhelminthes • Cestoda = tapeworms • hermaphroditic = having both ovaries and testes (being both sexes at the same time) • Head is scolex;segments are proglottids • See figure 12.26 • typical tapeworm:
Tapeworm life cycle • 2 hosts: • intermediate host: infected by ingesting tapeworm eggs; contains larval cyst in skeletal muscle and other organs such as brain (infection is called cysticercosis) • definitive host: infected by ingesting larval cyst; adult tapeworm grows in intestine • examples • Taeniasaginata = beef tapeworm • Taeniasolium = pork tapeworm
Tapeworms • life cycle of porktapeworm (Taeniasolium)
B. Aschelmenthes or Nematoda • roundworms • plain, unsegmented worms ranging from microscopic up to about 12 inches • Ascaris spp. • Ascariasis = intestinal infection • the largest roundworms: up to 12 inches • Pg. 736 • 1/4 of world’s population infected (around 2 billion people!) • infection by ingesting worm eggs that can remain in soil 10 years!
Trichinellaspiralis • trichinosis = larval cysts in skeletal muscle • infection by ingesting larvl cysts in undercooked pork or bear meat • See pg. 737for life cycle
Nematoda, cont’d • Wuchereriabancrofti • filariasis = worms in lymph vessels • microfilaria larva transmitted by Culex spp. mosquitoes • grow to adults 2—3 inches long • block flow of lymph • if untreated, after years of infestation, leads to elephantiasis (swelling due to accumulation of fluid in tissues)
Filariasis life cycle mosquito ingestsmicrofilaria microfilaria mosquitoinjectsmicrofilaria adults inlymphvessels adult worms blocklymph vessels
Now it’s time for the viruses ! • ‘virus’ is the latin term for _______ • “ a piece of bad news wrapped up in protein” • virology • the study of viruses
A.General nature of viruses • _____________: have only some of the characteristics of life • no metabolism • able to reproduce only with considerable help from host cell • No ribosomes! • No plasma membrane • obligate intracellular parasites: can reproduce only inside of living host cells • will not grow on artificial media (agar, etc) • do exist outside of host cells; e.g. some are transmitted through the air • high mutation rate • Viruses and Bacteria compared • see table 13.1
B. Size of viruses • SMALL: 20-1,000 nm (1nm = 1/1000 µm) human cell nucleus bacterium with virus inside
C. Structure • NOT _____: much less complex • neither procaryotic or eucaryotic • individual units called virions or particles • “virion” is to virus as “cell” is to a unicellular organism • Every virus has a core of nucleic acid (genes) • either DNA or RNA, never both • either nucleic acid may be single or double stranded • called the genome
Every virus has a coat of protein (the ______) around the nucleic acid • the capsid protects the genome • the capsid gives shape to the virus • Generally, the capsid is subdivided into individual protein subunits called capsomeres
Some viruses have an outer _________ of fat, protein and carbohydrates • derived from cell membrane of host cell • some envelopes may have spikes (carbo-protein molecules with viral specific components) in order to attach virus to host cells
virus without envelope • ( a nonenvelopedvirion )
D.Host and tissue specificity • most viruses are _________ (infect only one or a few species of hosts) • most viruses are tissue specific (infect only one kind of host tissue) • ____________: the species that a pathogen can infect
E.Viral replication (reproduction) and how viruses cause disease • 5 steps (could view as vulnerabilities for control) • 1. _____________: to host cell
virus penetrating host cell • 2. Entry or Penetration: into host cell • either whole virus or just nucleic acid (protein and envelope may be left behind) • either into cytoplasm or nucleus of host cell
viral replication, cont’d • 3. ____________________: • A. replication of viral nucleic acid (may dissolve host genes to get ingredients) • B. synthesis of viral protein: viral genes take control of host ribosomes and direct synthesis of viral protein • 4. ________________: assembly of new virions — up to several hundred • 5. ____________ of new virions • enveloped viruses escape one-by-one, taking along some cell membrane for their envelope (a budding process)…host cell may survive • other viruses may rupture host cell to escape • About 3,000 to 4,000 virions are released from a single cell infected with poxviruses, whereas a poliovirus-infected cell can release over 100,000 virions!
The Bacteriophages • viruses that infect bacteria • can wipe out a bacterial culture • sometimes just called “phage” • the easiest viruses to grow • subject of much research • They often make the bacteria they infect more pathogenic for humans!
Cell lysis vs. lysogeny • in the replication cycles for bacteriophages and animal viruses, the infection may not result in cell lysis • virus incorporates its DNA or its RNA (via DNA) into a chromosome of the host cell • virus is propagated each time the cell’s chromosome is reproduced • lysogeny= the conditon in which viruses and bacteria coexist without damage to each other • See figure 13.12 (next slide)
More on lysogeny • Host’s DNA is not destroyed & viral genome remains inactive in the cell • a “hibernating” virus for generations…then excised later to a lytic virus? • Many bacteria that infect humans are lysogenized by phages! • Some phage genes in the bacterial chromosome cause production of toxins or enzymes that cause pathology in humans! (e.g. the diphtheria toxin is a bacteriophage product; C. diphtheriae without the phage are harmless! )
F. Classification of viruses • Based on type of nucleic acid, strategy for replication, and morphology • Virus family names end in -viridae • Genus names end in -virus • A viral species shares the same genetic information and niche • Example: Family Herpesviridae,genusSimplexvirus, human herpesvirus 2 • See table 13.2 for reference of the families of viruses that affect humans
A closer look at one RNA virus: a retrovirus • Retroviridae, genus: Lentivirus, HIV • retroviruses carry their own enzyme, called__________________ • this enzyme uses viral RNA to synthesize DNA (reversal of the usual biochemical direction) in the host cell • this newly synthesized viral DNA integrates into a host cell’s chromosome as a provirus HIV is an example
_____ • name of virus: human immunodeficiency virus • common name: AIDS virus • But AIDS denotes only the final stage of a long infection • nucleic acid: ss-RNA w-envelope, 2 identical strands of RNA • a retrovirus • once in host cell, changes to DNA and is incorporated into host chromosome
HIV • related viruses: most mammals have similar viruses • distinguishing features: unusual spikes (______), reversetranscriptase
