• Kingdom Animalia: eukaryotic, no cell walls, heterotrophic nutrition, specialized tissues

• Flatworms
– e.g. planarians

• 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

• _________________ = 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)
____________________

• 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/monstersinside-me/

• 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:

• 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

• life cycle of pork tapeworm
(Taenia
solium)

• Endoscopic views of tapeworms in human intestine

• 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 life cycle

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

• 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)

• microfilaria
Filariasis life cycle mosquito ingests microfilaria mosquito injects microfilaria ad ults in lymph vessels adult worms block lymph vessels

• ‘virus’ is the latin term for _______
• “ a piece of bad news wrapped up in protein”
• virology
– the study 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

• SMALL: 20-1,000 nm (1nm = 1/1000 µm) human cell nucleus bacterium with virus inside

• 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 )

• 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

• 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

• 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!

• 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)

• 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! )

• 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

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

HIV infecting a
T cell

• Fig. 13.19

• 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

• 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

• 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….

• 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

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

• 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

• 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

• 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

• 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

• 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

• 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
)

– 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!

• 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?

• The Microbial World has now been surveyed