Download Biology: Infectious Diseases

Biology: Infectious Diseases
Germ Theory (Chapter 14.2 Revisited) and Chapter 39 (Infectious Diseases)
Throughout history, people have created explanations for disease. The introduction of the germ theory led
to the understanding that many diseases are caused by microorganisms. Changes in health
practices have resulted from the acceptance of the germ theory of disease.
Pasteur’s and Koch’s experimentation and hypotheses led to an understanding of the presence of
microorganisms and their relationship to diseases.
Spontaneous generation
1. Is the hypothesis that life arises from nonliving material
a. mice from grain
b. bees from carcasses
c. maggots/flies from rotting meat
2. Francesco Redi (Italian physician)
a. In 1668, he hypothesized that flies laid eggs on meat, which became
maggots-To disprove spontaneous generation
b. Set up experiment
1) One set of jars contained meat with no covering
2) Another set of jars contained meat with gauze covering
3) All meat spoiled, but the uncovered meat produced maggots;
covered meat did not
3. Louis Pasteur
a. In the mid 1800’s he set out to prove that spontaneous generation did
not occur, even when air was present
1. Boiled nutrient broth in a flask with a curved neck
2. After one year, no microorganisms grew in it
3. He broke off the neck and microorganisms were present after
one day
4. Biogenesis-the idea that living organisms come only from other living
organisms
5. Koch’s postulates history-The German scientist developed this in 1876.
 He looked at what caused anthrax that mainly affect sheep and cattle but could affect
humans too. He discovered under a microscope that a rod-shaped bacterium in the
blood was found in dead animals affected by anthrax.

He cultured the bacteria in nutrients and then injected healthy animals with it and
those animals became sick and died.
 He extracted the bacteria out of both blood cultures and compared them to each
other and the bacteria were the same.
o Koch’s postulate:
 The pathogen [disease producing agents -that disrupts the
homeostasis in the body (from bacteria, protozoans, fungi, viruses,
and other parasites) that come from soil, contaminated water,
infected animals, and including humans]must be found in the host in
every case of the disease.
 The pathogen must be isolated from the host and grown in sterile
conditions cultures.
 The pathogen from the culture must be placed in a healthy organism
and become sick with that disease.
 The pathogen then must is isolated from the new host and be shown
that it is the original pathogen.
1
Pathogens can transmit diseases in four main ways.
1. Direct contact (to include the exchange of body fluids from kissing or sex)
2. By an object (to include countertops, sinks, cups, utensils, straws, toilets, door handles, toys, and
towels)
3. Through the air (mucus droplets from coughing and sneezing)
4. Intermediate organism called a vector (mainly arthropods-insects like ticks, flies, mosquitoes, etc)
Not all microorganisms are pathogenic. Some are actually beneficial and living inside us or on our skin.
Humans develop normal flora as we are coming through the birth canal. Staphococcus epidermis
and Propioibacterium sp. produce fatty acids that inhibit growth of fungi and yeast on our skin. As
we are feed and handled we obtain more normal flora to include areas such as Upper respiratory
system, lower urinary and reproductive tracts, and the lower intestinal tract.
Modern health practices emphasize sanitation, the safe handling of food and water, aseptic techniques to
keep germs out of the body, and the development of vaccinations and other chemicals and
processes to destroy microorganisms.
An antibiotic is a substance produced by a microorganism that, in small amounts, will kill or inhibit the
growth and reproduction of more pathogens. They are produced natural from bacteria and fungi.
They can’t be used for viruses. Antibiotics can kill normal flora allowing yeast infections to occur
especially in women.
Immunity
Innate immunity: Our White Blood cells defend against invasions by pathogens.
 Also the body’s earliest line of defense against pathogens.
o Phagocytes are white blood cells that engulf and destroy bacteria. If the infection is small
and contained to one area then a reddish swollen place will form just under the skin –
inflamed area (hot to the touch)
Acquired Immunity: The defense mechanism in our body that gradually builds up immunity. (Days to
weeks)
 Antigens (the foreign substances) are usually proteins present on the surfaces of whole organisms
such as bacteria, or parts of the organism like pollen from plants. When present our immune
system goes on alert and responds to it by producing antibodies against it.
 Antibodies in this case are proteins found in the blood that attack the antigen.
o The antibody molecule is Y shaped and has two identical antigen-binding sites that
precisely fit the shape of a specific antigen.
o The overreactions of the immune system are known as allergies.
 Allergies occur when antigen binds to mast cells, which are a type of immune cell
found throughout the body, but especially in the lining of nasal passages. These
mast cells release chemicals called Histamines. Histamines increase the flow of
blood and fluids to surrounding areas and cause sneezing, runny nose, runny eyes,
and coughing, dropping of blood pressure, hives, etc –allergic reactions so you
need antihistamines to get rid of the symptoms.
 Asthma is triggered when antigens from allergic reactions becomes worse.
 Asthma is a condition in which smooth muscles contract around the
passages leading to the lungs, make it difficult to breathe.
 The Lymphatic System creates a line of defend against foreign agents when infections spread. The
lymph nodes can become swollen and tender to the touch showing that they are battling the
infection.
o The Lymph nodes are small masses of tissues that contain Lymphocytes (type of White
Blood cell) and filters pathogens from the lymph.
 Tonsils are large clusters of lymph tissue that provide protection from against
bacteria and other pathogens that enter the mouth and nose.
2


Spleen is an organ that stores a certain type of lymphocytes. It also filters out and
destroys bacteria and worn-out Red Blood cells, and acts as a blood reservoir.
Thymus gland is located above the heart and stores immature lymphocytes until
they mature and then releases them into the body when needed.
 T cells are a type of lymphocyte that is produced in the bone marrow and
processed into the thymus gland.
o Two types Immunity
1. Cellular Immunity: Helper T-cells (Identifies foreign cells
and stimulates other cells to fight infection-help in the
production of plasma cell and the production of antibodies)
 Interact with B cells a type of lymphocyte
white blood cell (bind to antigens directly
and formed in the Bone Marrow) –produces
antibodies.
 As B cells develop, the genes that code for
antibodies rearranges themselves to match
with the type of cell that they are in.
 The antigens activate a small fraction of the
body’s B cells to rapidly grow and
reproduce in large populations to
specialized B-cell called plasma cells that
release the antibodies.
o T cells mature in the Thymus gland
and release chemicals that cause B
cells to produce clones of plasma
cells and to produce the antibodies.
 Some B cells remain in the blood stream and
become Memory B cells that will invade in
future invasions of the pathogen.
 Cytotoxic T cells differentiate and produce
identical clones. They travel to the infection
site and release enzymes directly onto the
pathogens causing them to lyse and die.-also
called Macrophage.
 Killer T-cells kills cancerous cells in the
body; also kills body cells that have been
invaded by pathogenic organisms
o Can cause rejection of transplant
organs
o Drugs like cyclosporine can be
given to patients with transplants
to suppress the Cell-mediated
immune response but must be
taken for the rest of their life and it
does not always work.
 Suppressor T-cells Slows down or stops the
activities of B-cells and other T-cells once
the danger of infection has passed
2. Passive and Active Immunity: Acquired Immunity
 Passive-develops as a result of acquiring antibodies
that are generated in another host- (Mother to child
for example)
3

Active-vaccine is a weakened, dead, or incomplete
portion of pathogens or antigens that, when injected
form an immune response.
Serious infections may allow pathogens to spread throughout the body. The immune response will cause
respond in two ways:
1.) More White Blood Cells
2.) A fever-The body releases chemicals that cause our temperature to increase.
 Indicates the body’s immune response to the pathogen has increased and the body
increases the temperature to kill the pathogens (Pathogens usually don’t like
higher than normal temperatures-often slows or stops the growth of
microorganisms)
Autoimmune Diseases: When the body cannot distinguish between “self” and “not self” the body starts
attacking its self. It can occur as a result of a bacterial infection.
 Examples:
o Untreated Strep Throat can lead to Rheumatic fever-attacking the heart
and possible death
o Rheumatoid arthritis-unknown what causes it but it attacks the joints
starting as early as your 30’s.
o Juvenile-onset diabetes can be caused by an autoimmune responseattacks the insulin-producing cells of the pancreas
o Multiple Sclerosis can first appear in your 20’s to 40’s and attacks the
myelin sheath that protects the nerve fibers. There is some evidence that
suggests that a viral infection can trigger this disease.
In 1957, scientists discovered that virus-infected cells produce a protein called interferon that helps other
cells resist viral infections and block viral replication. This has led to medications to kill viral infections.
 Viral particles are covered with antigen sites so when antibodies attach to those
sites the process called agglutination –viruses become one large mass link and can
no longer enter cells and phagocytes will take care of the masses. (This process
occurs in bacterial infections too.)
Viruses
Viruses are nonliving infectious agent that cause diseases in all five Kingdoms (See shapes in Chapter 18.1)
 Structures that can only replicate with a host cell usually bacteria called a bacteriophage.
 Its host is a cell having specific molecular groups (recognition sites) at its surface to
which the virus can selectively bind to.
 Once bound, the whole virus or its nucleic acid alone enters the cell’s cytoplasm,
where the virus survives
 Viral coat is called a capsid and surrounds the nucleic acid
 Two types: RNA and DNA
 In some viruses, the capsid is enclosed in an envelope derived from the lipid bilayer
of a host cell membrane
 Two Replication Cycles: Infectious Cycles
 Usually, many new viral particles are assembled and released together, either by
budding from the host cell or through a rupturing of its plasma membrane (lysis)
cause the death of the host cell.
4
1.
2.
Lysogenic cycle: (See diagram in Chapter 18.1)
 Attachment and entry of virus which invades the host cell
 Provirus becomes part of the host chromosome (Provirus
formation)
 Latent viral DNA or RNA passed on to successive generations of
bacteria or host cells by cell division-does not kill the host cell
 The virus stays in a latent state until it spontaneously converts to
the Lytic cycle.
Lytic cycle: (See diagram in Chapter 18.1)
 Attachment and entry of virus which invades the host cell
 Replication of virus
 Assembly of viral particles (followed by synthesis of viral proteins)
 Lysis of the host cell and release of about 200 viruses-kills the host
cell
Classification of Animal Viruses
I.
DNA Viruses:
a. Adenoviruses-can cause acute respiratory tract infections: and under some circumstances
can cause malignant tumors in hamsters
b. Parvoviruses-Hepatitis A
c. Papovaviruses-Warts in humans, rabbits, dogs; some cancers in mice and hamsters
d. Herpesviruses-Fever blisters, chickenpox, shingles, genital herpes, some induce cancers,
Epstein-Barr virus-mononucleosis
e. Poxviruses-smallpox
II.
RNA Viruses:
a. Enteroviruses-diarrhea, polio, aseptic meningitis
b. Rhinoviruses-common colds
c. Togaviruses-Yellow fever, German measles (rubella), equine encephalitis
d. Influenza viruses- Flu
e. Paramyxoviruses-measles, mumps
f. Rhabdoviruses- Rabies
g. Arunaviruses-Meningitis, hemorrhagic fevers
h. Coronaviruses- upper respiratory disease
i. Retroviruses-Sarcomas tumors, leukemia, and AIDS
j. Reoviruses-severe diarrhea
AIDS: Acquired Immune Deficiency Syndrome is caused by a Retrovirus called human immunodeficiency
virus (HIV)-When the virus enters the body from contaminated blood or sexual intercourse, it attaches to
receptors on the surfaces of Helper-T-cells. The disease kills the immune system and causes infections such
as from protozoans and/or fungus and possible rare forms of cancer that normally the body can fight against.
It can take 6 months to 10 or more years to develop but it usually fatal.
Another note: Mothers-to-be with HIV can pass it on to her baby too.
5
Kingdom Monera
Archaebacteria (three types)-oldest, live in extreme conditions, prokaryotic, and unicellular-chemotrophic
autotrophs prokaryotes
1. Methanogens –have the ability to harvest energy by converting H2 and CO2 into methane
gas.
a. Obligate anaerobes (can’t live in the present of oxygen)
b. Found in marshes and the intestinal tracts of humans and some animals
2. Halophiles-salt-loving (live in salt lakes and other areas with high salt contents)
3. Thermoacidophiles-found in areas of extreme acid conditions and in areas with very high
temperatures (temps reaching 230 F and pH below 2)
Eubacteria (4 main types-more common and more complex than Archaebacteria)-Heterotrophs prokaryotes
1. Cyanobacteria (blue –green algae) –photosynthetic (led to the diversity of life by allowing
oxygen into the atmosphere)-autotrophic
2. Spirochetes-gram negative, spiral-shaped, and heterotrophic
a. Some live in the presence of oxygen and some don’t
b. Some are parasitic or free living
3. Gram-positive (some are in this category but not gram positive)
a. Strains of Streptococcus cause strep throat
b. Some are used to make yogurt
c. Many produce our antibiotics
4. Proteobacteria (largest)
a. Many Gram-negative
b. Divided into three subgroups
i. Enteric bacteria-live mainly in our intestinal tracts
ii. Chemoautotrophs-oxidize chemicals in minerals to obtain energy
iii. Nitrogen-fixing bacteria-essential to many ecosystems

Bacteria range between 1 to 10 micrometers in width and can be spiral (spirillum), spherical
(coccus/cocci), rod-shaped (bacillus), or bacillus with endospores.
6




Bacterial Movement- Some have one or more flagellum, some spiral or lash forward, and some glide
slowly along a layer of slime-like material that they secrete themselves.
Bacterial growth and reproduction: Bacterial growth can happen as often as every 20 minutes.
o Binary Fission: When a bacterium has grown nearly double in size, it replicates its DNA and
divides in half, producing two identical daughter cells. –Asexual reproduction (Most
common form)
o Conjugation: Sexual reproduction that exchanges genetic information. A long bridge of
protein forms between and connects two bacterial cells. Part of the genetic information
from one cell, called the donor, is transferred to the other cell, called the recipient, through
the bridge. When completed the recipient cell will have a different set of genes from the
donor. The Genetic diversity allows the bacteria a better survival rate even if the
environmental conditions change.
Bacteria can survive in unfavorable conditions with adaptations: Many types of bacteria can
form spores during unfavorable conditions. An endospore is one type of spore that forms a thick
internal wall around the bacterium that encloses its DNA and a portion of cytoplasm. It can stay
dormant for years but when conditions are favorable to grow it will.
o Some bacteria form toxins. It is important to properly store foods and cook canned foods as
directed to avoid food poisoning.
 Example: Clostridium botulinum causes Botulism a rare form of food poisoning that
can be fatal. Botulism can grow in cans if they are not sealed properly and will
interfere with nerve activity, cause paralysis, and if breathing muscles are
paralyzed, death will occur.
Importance of Bacteria:
o Used to produce many food products: beverages, cheese, yogurt, buttermilk, sour cream,
pickles, wine, and even vinegar
o Used in industries: One type digest petroleum, some remove waste products and poisons
from water, help with mining, synthesizing drugs and chemicals through genetic
engineering, and sewage decomposition-sewage treatment plants
o Environmental Relationships: Symbiotic relationships with every Kingdom.
 Keep us healthy: Symbiotic relationships within our body keep us healthy. Bacteria
on the skin and inside our bodies and some of them make vitamins for us that we
cannot produce on our own.
 Cattle and other animals that eat grass need bacteria that are in the intestines to
form enzymes needed to breakdown cellulose.
 Saprophyte bacteria recycle, decompose, or breakdown, dead material.
 Nitrogen-fixed bacteria allow nitrogen gas to be broken down into a usable formimportant for the Nitrogen cycle
Kingdom Protista-can be unicellular, colonial (all the cells are similar with similar generalized functions), or
multicellular eukaryotic organisms.
 All need some kind of a water-based environment
 Major component of plankton
 Many can form cyst in adverse conditions
 In three major categories (protozoa, algae, and fungus-like plants)
1. Protozoans-animal-like
a. Some ingest food by phagocytosis
b. Some have mouth-like structures
c. Others use pseudopodia (false foot) to move and engulf food
7
i. Division Rhizopoda (Amoeba genus) –freshwater, unicellular, and have a
pseudopodia (a false foot for locomotion)-often called Sarcodina protists with
false feet. Some varieties of foraminifers, heliozoans and radiolarians produce
external glass-like shells made of Silica or Calcium carbonate to help support
their unusual shapes.
ii. Division Apicomplexa-all parasites that are nonmotile, and all form tiny,
infectious spores- often called Sporozoans. Asexual reproduce by spore
formation Examples: Plasmodium –malaria from a mosquito and TrypanosomaAfrican Sleeping sickness from a tsetse fly
iii. Division Zoomastigophora- some are parasites, some free living, and some
using other types of symbiosis. Move in water with one or more flagellum.
Often called flagellates. Reproduce by binary fission (asexual) and sexually by
gamete cells in Meiosis.
iv. Division Ciliophora (Paramecium genus)-solitary, fresh water organism with
cilia for movement. Sexual reproduction by conjugation is possible but usually
asexual reproduction by binary fission-a form of mitotic cell division
Paramecium
8
2.
Algal Protists
i. Division Dinoflagellata (members of phylum Pyrrophyta-Fire Protist because
of bioluminescence)-are different shapes and sizes, and bioluminescent –blue
colored (because made of glass). Some are not photosynthetic because they
lost their chloroplasts over time and are now heterotrophs. Most have two
flagella and swim. Many dinoflagellates have thick plates looking like armor.
Reproduce by binary fission.
 Dinoflagellates don’t have histones-special proteins usually tightly
bound around their DNA-all other eukaryotes do.
 Some have complex lifecycles that involve cysts. Organisms with this
cyst can be toxic. Pfiesteria forms a cyst and forms toxins harming fish
and human during algal blooms-red tide. Gonyaulax polyhedron is
another that forms toxins in the water during algal blooms-red tide
killing fish, clams, oysters, and even kill dolphins. If we eat affected
shellfish we can become very sick and possible die.
Dinoflagellate
ii. Division Eugelenophyta (Euglena genus)-Have a anterior flagellum, have
chloroplast and are photosynthesis as well as using phagocytosis, lightsensitive and have a eyespot (stigma) which is not a true eye but
photoreceptor.
9
iii. Phylum Chrysophyta: Golden Protists -Yellow-green algae, golden-brown
algae, and diatoms. The cell walls contain carbohydrate pectin instead of
cellulose, and usually store food in the form of oil instead of starch. They
reproduce asexually and sexually. Most are solitary but some form threadlike
colonies.
 Diatoms have cells rich in silicon. Some have glass cell walls. The
walls are etched in fine lines and designs. They are photosynthetic and
are among the most abundant and beautiful species in the oceans.
Diatom
3.
iv. Division Chlorophyta (green algae)-many are multicellular and reproduce by
Alternation of generations (sexual and asexual cycles)-Sometimes listed in the
Plantae Kingdom
a. sporophyte-produce spores
b. gametophytes-produce gametes (egg and sperm-each 1n)
c. zygote-developing egg (2n)
v. Division Phaeophyta (brown algae)-Multicellular and live in marine temperate
zone and coastal areas and reproduce by Alternation of generations-sometimes
listed in the Plantae Kingdom
vi. Division Rhodophyta (red algae) Multicellular and live in marine zones
(especially tropical areas) and reproduce by Alternation of generationsSometimes listed in the Plantae Kingdom
Fungus-like Protists-Sometimes included with Fungi Kingdom as Oomycota Phylum
i. Division Myxomycota (slime molds)
a. Multicellular and mobile by pseudopodia
b. Often brightly-colored yellow or orange
Evolution of Protists: According to Margulis’s Endosymbiont Hypothesis, these prokaryotes lived within
another moneran as endosymbionts (symbiotic organisms that live within another organism, which is called
the host organism). The endosymbionts and their host cells formed an effective team but eventually they lost
their independence, and had to live together. This gave rise to the organelles that we observe in eukaryotic
cells and the first eukaryotes –Protists.
10
Helpful Protists Relationships:
 Trichonympha is a Zoomastiginan that lives in the intestines of termites and wood roaches. They
need the protist to supply the enzyme needed to break down the cellulose in the wood. –Symbiotic
Relationship
 Many protists live in the ocean or freshwater are food for larger organisms. Essential food source for
large fish in the ocean.
 Many coral have a symbiotic relationship with dinoflagellates
 Plant-like phytoplankton essential part of a food web in the fresh water and ocean environments.
Kingdom Fungi
 Eukaryotic and are heterotrophs that absorb (not ingest) their food
 Reproduce asexually (Fragmentation or spores)and sexually (each hydra forms a gametangium
structure-gamete-forming structure that fuse to one another along with some of the nuclei pair to
form zygote nuclei)
o Saprophytes absorb nutrients from dead organic matter-decomposers
o Parasites absorb nutrient from a host body
o Mutualism symbiosis –two organisms benefit from one another
 Example-mycorrihizae (or rhizosomes)-are special fungi that live in/on the roots of
plants, especially trees.
o The body of the fungus is called a mycelium-a tangled network of filaments (each filament is
a hypha)
I. Divisions Zygomycota (Common Molds)-sexually produce by
zygosporangium-zygospores which remain dormant until conditions
are right when they release spores.
 Hyphae lack cross walls between nuclei
 Example –Black bread mold Zopus stolonifer
II. Divisions Ascomycota (Sac Fungi) -primarily reproduce asexually by
forming chains of spores called conidia.
 In sexually reproduction-cup-like fruit structure called
ascocarp (contain a number of asci-each contain 8 ascospores)
III. Division Basidiomycota (mushrooms)-Club Fungi
 Mycelium of the mushroom starts one place and spreads out
from there in a circle-hyphae forms fruiting structures called
basidiocarp (the mushroom)
IV. Division Deuteromycota –Fungi imperfecti-meaning lack of a sexual
reproduction phase
 Asexual-conidia on conidiophores
 Responsible for ringworm, athlete’s foot, and on plants-black
spot on roses and tomato blight
11
V. Lichens-mixture of fungus (often ascomycete)and either a green alga
(Chlorophyta) or a bluegreen alga (Cyanobacteria) that live in a
Mutualistic symbiotic relationship
 Not a division but an association
Fungi Importance:
 The principal role in the environment is to decompose and recycle living material -Found almost
everywhere on Earth
 Some mushrooms are edible while others are poisonous and/or cause hallucinations
 Yeast forms are used to make breads and alcoholic beverages-Genus Saccharomyces is the most
common yeast used

Cause diseases in plants and animals
12