Chapter 21Parasites and Pathogens

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Chapter 21--Parasites and Pathogens
Hosts for the West Nile Virus
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Fig. 21.1c
While horses and humans can be infected with west
Nile, they dont transmit it to others.
Mosquitos spread the disease from host to host.
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Microbes--Diversity on Earth is Enormous--Most
living things are microbes. Some are incredibly
helpful, some are harmful. Activities--Ecological
Contributions--Nutrient Recycling, Food Products
(remember civilization??), Healthy
Microflora. Pathogenicity--Disease causing
microbes are pathogens. Toxins--Small molecules,
parts of proteins, parts of bacterial cell wall
released when bacteria die--these are poisonous
and cause disease. Epidemiology--Study of
factors that influence transmission and
distribution of diseases in human population.
Infectious diseases are caused by a pathogen.
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Fig. 21.2
Helpful microbes.
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Fig. 21.3
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Fig. 21.4
Four modes of disease transmission.
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1. Viruses

• Viruses require a host
• Viruses are essentially packets of genetic
  information RNA or DNA.
• Viruses can be latent.
• Viruses are specific for different cell types.
• Polio virus infects nerve cells
• HIV infects immune T cells
• Hepatitis B infects liver cells
• Essentially, Viruses are composed of
• Envelope
• Caspid (capsule that holds genetic material)
• Genetic Material, RNA or DNA
• RNARetrovirus

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Virus Life Cycle

• 1. Binding--this requires specialized envelope
  proteins. These proteins make viruses specific
  for different cells.
• 2. Penetration--viral particles enter the cell,
  the caspid is removed and genetic material enters
  the nucleus.
• 3. Replication--the virus uses the host
  replication machinery to make many copies of
  itself.
• 4. Viral protein production--the virus uses the
  hosts translation machinery to make many copies
  of the viral proteins that will be used for the
  capsid and new envelope proteins. Envelope
  proteins move to the plasma membrane thanks to
  protein secretion performed by the host.
• 5. Assembly--genetic material is packaged into
  the new caspids.
• 6. Budding--the caspids move to the cell
  membrane, get wrapped in their envelope proteins
  and move on to infect a neighboring cell.

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Fig. 21.5
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Fig. 21.6
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Table 21.1
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Fig. 21.7
Chickenpox on left, shingles on right. Both are
caused by viral infections. Herpes zoster
infects sensory nerve tissue and can cause
shingles.
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Fig. 21.9
Measles on left, smallpox on right. Read the
health focus (p425) on smallpox. We have
eradicated this disease, but samples remain in
freezers. Is this important? Is this safe?
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2. Bacteria Basics

• Bacteria are
• Sometimes Symbiotic
• Divide Asexually by Binary Fission
• Form Endospore
• Motile
• Reproduce every 20 min
• Highly mutable
• Produce Toxins
• Bacteria vary greatly. For the most part, all
  have
• Cell wall for protection
• Plasma membrane
• Capsule outer protective layer
• Ability to move
• Sense attractants/repellants
• Genetic material--DNA wrapped in a loop

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Pathogens

• Pathogenic bacteria are those that produce toxins
  and can cause an illness.
• Because bacteria reproduce so fast, severe
  problems can arise very quickly.
• Bacteria are treated with Antibiotics, which
  target the cell wall, block key metabolic
  pathways and bacterial reproduction.

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Fig. 21.10
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Fig. 21.11
Gram staining distinguishes bacteria based on the
structure of the coat. Gram-positive bacteria
have a sugery-protein coat that soaks up the dye.
Gram-negative bacteria have an outer membrane
that surrounds the sugery-protein coat and
prevents the dye from binding. This test is a
quick way to screen bacteria and lead to
identification of a pathogen.
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Table 21.2
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Fig. 21.12a
Streptococcus pyogenes (a) can cause Impetigo (b)
or can even cause flesh-eating disease depending
on the presence of virulence factors. These
factors are produced by bacteria, called M
proteins, and help prevent the bacteria from
being captured and destroyed by white blood
cells. See the text for (c)--flesh-eating
disease. M proteins destroy connective and
muscle tissue because they release enzymes.
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Fig. 21.13a
TB (Tuberculosis) is a chronic disease caused by
Mycobacterium tuberculosis. About 24,000 new
cases of TB are reported each year, and about
12,000 deaths are caused in the US. This
bacteria causes lesions or open spots that grow
into dense structures called tubercules. These
tubercules eventually can be destroyed, but then
the scar tissue left calcifies and leaves spots
on the chest.
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Fig. 21.14a
X-rays of normal and infected individuals. TB
can be treated with antibiotics, but increasing
antibiotic resistance is a huge concern. Note
the condensation of the infected individuals
lungs.
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Fig. 21.15
Food poisoning can be caused by a variety of
microbes. These microbes release toxins which
act on our cells. Boiling usually kills the
bacteria, but not the toxin, so it is critical
that food not be left in a place where bacteria
can grow. Clostridium botulinum is shown
above--this causes lock jaw. Spores survive hard
conditions (canning)!
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Fig. 21.16
Athletes foot is caused by Trichophyton--a
pathogenic fungus.
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Table 21.3
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Fig. 21B
Anthrax spores are shown above. This is one of
the pathogens that has potential (more than
potential??) to be used as a bioweapon.
Bioweapons are not new!! 600 BC--Assyrians
poisoned wells with ergot (fungus that makes
LSD). 1346--Tartars tossed plague infected
bodies over the walls of Kaffa. Napoleon spread
swamp fever in Italy. 1984--cult in Oregon
infects salad bar with Typhoid. 2001--Anthrax
spores on letters sent to media and congress
representatives. Could The Stand really
happen????
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Other Bioweapon pathogens

• Smallpox--caused by Variola virus--highly
  contagious. Stores in US and Russia. Fever and
  headache after 12 days of exposure--then a rash.
  Most of us do not have immunity.
• Plague--caused by bacterium Yersinia
  pestis--inhaled form most potent, not as
  contagious as smallpox.
• Botulism--just a small amount of the toxin leads
  to blurred vision and lockjaw, death can result
  in 24 hours. Immediate antibiotic required.
• Hemorrhagic fevers--Hot Zone--Marburg, Ebola
  viruses. Respond to antivirals.

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Fig. 21.18
Life cycle of Plasmodium vivax, a protozoan
(eukaryotic unicellular organism) that causes
malaria. The vector that carries the Plasmodium
is the Anopheles mosquito.
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Fig. 21.19
Giardia, which causes Giardiasis, is the most
common waterborne diarrheal disease in the US.
This microbe can produce cysts which are
resistant to filtering or chlorine. These cysts
pass through feces and can spread the disease
(daycare centers are very susceptible). 7 of
the US population is thought to carry Giardia.
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Table 21.4
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Fig. 21.20
Worms are yet another parasite that seek to live
off of us. The life cycle of the blood fluke is
shown here. Shistosomiasis is the disease
produced. The fluke in water moves into the skin
of a human and migrates to the lungs and veins of
intestines. Large masses of eggs are produced
and this produces swelling--huge bellies, liver
and spleen too--can result. 250 million people
worldwide are infected and 500,000 people die
from the blood fluke.
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Fig. 21C
Antibiotics anyone??? Magic bullets or Immune
system destroyers?