Worms Parasitic Worms Kingdom Animalia eukaryotic no cell

Worms!

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 and testes

Clonorchis sinensis (Chinese liver fluke)

Liver fluke life cycle

Schistosoma: blood flukes, male and female (in groove on males body) __________

Schistosoma haematobium • 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 • Monsters inside me…. check it out!!!!: http: //animal. discovery. com/videos/monstersinside-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 – Taenia saginata = beef tapeworm – Taenia solium = pork tapeworm

Tapeworms • life cycle of pork tapeworm (Taenia solium)

• Endoscopic views of tapeworms in human intestine

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 – 1/3 of world’s population infected (over 2 billion people!) – infection by ingesting worm eggs that can remain in soil 10 years!

Ascaris lumbricoides

Ascaris life cycle

• Trichinella spiralis – trichinosis = larval cysts in skeletal muscle – infection by ingesting larval cysts in undercooked pork or bear meat • See pg. 737 for life cycle

Figure 25. 20

Nematoda, cont’d • Wuchereria bancrofti – 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 ingests microfilaria • mosquito injects microfilaria adults in lymph vessels adult worms block lymph vessels

elephantiasis

Elephantiasis

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 (1 nm = 1/1000 µm) human cell nucleus bacterium with virus inside

Fig. 13. 1

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 nonenveloped virion )

enveloped virus

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!

Release by budding

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!

bacteriophage

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)

Lytic Cycle vs. Lysogenic Cycle (fig 13. 12)

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, genus Simplexvirus, 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’s RNA becomes DNA and enters host chromosome

HIV • related viruses: most mammals have similar viruses • distinguishing features: unusual spikes (______), reverse transcriptase

HIV infecting a T cell

HIV budding from infected host cell

• Fig. 13. 19

Figure 19. 14

Another RNA virus worth noting… • The Influenza Virus • Figure 24. 15 • www. flu. gov

Another interesting ‘family’ of viruses are the Herpesviridae • DNA viruses, nearly 100 herpesviruses known • important diseases in this group include – Human herpes Simplexvirus • type I: cold sores (fever blisters) HHV - 1 • type II: genital herpes HHV - 2 – Chickenpox: HHV - 3 (Varicellavirus) – infectious mononucleosis: HHV - 4 – Cytomegalovirus: HHV-5 – Kaposi’s sarcoma: HHV-8 – Others, too see pg. 404 • classic examples of ____ viral infections

Latent infection • some viruses enter host cell and remain dormant or replicate slowly with little damage to host cell • may activate later upon some stimulus • herpes viruses produce latent infections • examples? – See table 13. 5

G. Detection of viruses • more involved and time-consuming than for bacteria. . why? • can inoculate viruses into fertilized eggs and look for characteristic changes due to viral replications • or inoculate suspensions of material to cell cultures (tissue cultures) and look for cytopathic effects (fig. 13. 9) • search for viral antibodies in the patients’ serum (serological tests) – Next slide….

Checking for viral antibodies

More ways to detect viruses • direct observation with an electron microscope • look for pathological signs in the diseased tissue • Use modern molecular methods to identify and amplify (PCR) the viral RNA or DNA

H. Inhibition of viruses • difficult because of few vulnerabilities of viruses: few structures, no metabolism

Inhibition of viruses • our body defenses • antiviral drugs of limited value so far – antiviral drugs block various steps in viral replication • such as AZT and acyclovir (Zorvirax) inhibit nucleic acid synthesis • protease inhibitors block an HIV enzyme needed for new viral coat assembly – how about antibiotics? Why not? • _____: antiviral proteins produced by human cells in response to a viral infection (protect healthy cells from viral damage by blocking various steps in viral replication)

• Viral _____: best method of controlling viruses at this time – controls specific viruses • See table 18. 2 for examples – many successful antiviral vaccines • Inactivated – Formaldehyde, phenol, lipid solvents, heat, UV light • attenuated

Cold Viruses • Gets at least half the population each year • Symptoms linked to hundreds of different viruses and viral strains (can have mixed infections)…will research in Pathogen Group 7 • Confined to closed spaces with carriers rather than “cold” temps. • #1 spread via contamination of hands with mucous secretions! • Portal of entry: mucous membranes of nose and eyes • Over 200 types

I. Viruses and cancer • relationship first demonstrated in 1908: chicken leukemias • cancer results from the uncontrolled reproduction of cells • scientists are uncertain as to all mechanisms that trigger a normal cell to multiply without control – however, they know that certain chemicals are carcinogens (cancer causing) • hydrocarbons in cigarette smoke • asbestos • certain pesticides and dyes • environmental pollutants in large amounts • physical agents such as UV light and X-rays also? • evidence that viruses are also carcinogens

Viruses and cancer • Some human (and many animal) cancers are known to be caused by viruses (oncogenic viruses) • Approx. _____% of cancers are known to be virus -induced • Examples: leukemias ( such as HTLV: human T-cell leukemia virus ) and other lymphatic cancers, cervical cancer (HPV), liver cancer (HBV) • Development of cancer also involves oncogenes and immune deficiency

Oncogene Theory • Developed in 1970’s • explains how viruses and other carcinogens transform normal cells into tumor cells • certain human genes can be transformed by carcinogens into oncogenes • once an oncogene, it can influence cellular growth to a higher than normal rate • 1989 Nobel Prize (Bishop and Varmus) for proving that the cancer-inducing genes carried by viruses are derived from animal cells

J. On to _____. . . • prions : infectious particles of protein only; no nucleic acid – prion research began with sheep scrapie – associated with several degenerative diseases of human nervous system/brain tissue (e. g. kuru and Creutzfeldt-Jakob disease, – Fatal Familial Insomnia – Long period of latency, then rapidly progressive and universally fatal (within one year)! • No known treatments • In 2003 a British patient died of CJD after receiving a blood transfusion in 1996 from a donor who had CJD. • CJD has also been transmitted through corneal grafts and administration of contaminated human growth hormone • The latest CDC guidelines for handling CJD patients should be consulted. (www. cdc. gov)

More on prions… – bovine spongiform encephalopathy, named for the brain’s appearance • known as mad cow disease • Acquired by humans who consumed contaminated beef • Was first incidence of prion disease transmission from animals to humans! • In 2003, isolated cows with BSE were found in Canada and U. S. – Transmissible Spongiform Encephalopathies (TSEs) – Result of an altered protein…see figure 13. 22 – Prions are resistant to disinfection, heat and autoclaving!

K. And viroids • viroids : infectious particles of naked RNA only; no protein – About one-tenth the size of an average virus! – so far, associated only with plant diseases – Viroids may have evolved from introns (figure 8. 11)…. speculation of animal viroids?

A milestone achieved… • The Microbial World has now been surveyed