Download virus

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
• See Chapter 23 ( page 666-667), figure 23.27
• 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
– 1/4 of world’s population infected (over 1.5 billion
people!)
– infection by ingesting worm eggs that can remain in
soil 10 years!
Ascaris lumbricoides
Ascaris in intestine
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
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
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 (1nm = 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
• see figures 13.2, 13.3, 13.4, 13.5
• 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
– See figure 13.6…plaques
• 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 ( see figure
13.19 )
• 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
• Cure?
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 , see pp.
629-632)
• 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