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
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 See Chapter 23 ( page 666-667), figure 23.27 Monsters inside me….check it out!!!!: http://animal.discovery.com/videos/monsters- inside-me/ 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 – 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!
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 ad ults in lymph vessels microfilaria mosquito ingests microfilaria mosquito injects microfilaria adult worms block lymph 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 nonenveloped virion )
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,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 chromo- some
HIV related viruses: most mammals have similar viruses distinguishing features: unusual spikes (______), reverse transcriptase
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….
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 what triggers 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)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