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 generation1. Is the hypothesis that life arises from nonliving material

a. mice from grainb. bees from carcassesc. 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 generationb. Set up experiment

1) One set of jars contained meat with no covering2) Another set of jars contained meat with gauze covering3) 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 neck2. After one year, no microorganisms grew in it3. He broke off the neck and microorganisms were present after one day

4. Biogenesis-the idea that living organisms come only from other living organisms5. 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.

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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.

ImmunityInnate 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.

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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)

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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 deatho 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 response-

attacks the insulin-producing cells of the pancreaso 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.

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1. 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.2. 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 VirusesI. DNA Viruses:

a. Adenoviruses -can cause acute respiratory tract infections: and under some circumstances can cause malignant tumors in hamsters

b. Parvoviruses -Hepatitis Ac. Papovaviruses -Warts in humans, rabbits, dogs; some cancers in mice and hamstersd. Herpesviruses -Fever blisters, chickenpox, shingles, genital herpes, some induce cancers,

Epstein-Barr virus-mononucleosise. Poxviruses -smallpox

II. RNA Viruses:a. Enteroviruses -diarrhea, polio, aseptic meningitisb. Rhinoviruses -common coldsc. Togaviruses -Yellow fever, German measles (rubella), equine encephalitisd. Influenza viruses - Flue. Paramyxoviruses -measles, mumpsf. Rhabdoviruses - Rabiesg. Arunaviruses -Meningitis, hemorrhagic feversh. 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.

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Kingdom MoneraArchaebacteria (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 heterotrophica. Some live in the presence of oxygen and some don’tb. Some are parasitic or free living

3. Gram-positive (some are in this category but not gram positive)a. Strains of Streptococcus cause strep throatb. Some are used to make yogurtc. Many produce our antibiotics

4. Proteobacteria (largest)a. Many Gram-negative b. Divided into three subgroups

i. Enteric bacteria -live mainly in our intestinal tractsii. 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.

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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 vinegaro 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 form-

important 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 phagocytosisb. Some have mouth-like structuresc. Others use pseudopodia (false foot) to move and engulf food

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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 Trypanosoma-African 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

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2. Algal Protistsi. 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, light-sensitive and have a eyespot (stigma) which is not a true eye but photoreceptor.

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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

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 sporesb. 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 generations-Sometimes listed in the Plantae Kingdom

3. Fungus-like Protists-Sometimes included with Fungi Kingdom as Oomycota Phylumi. Division Myxomycota (slime molds)

a. Multicellular and mobile by pseudopodiab. 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.

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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-decomposerso Parasites absorb nutrient from a host bodyo 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)

Stolon is a small vine-like structure that produces myceliumo Sporangium is spore containing structure. o Chitin is the complex carbohydrate that gives fungi its strong cell walls.

I. Divisions Zygomycota (Common Molds and saprobes)-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 Some are saprobes and have a symbiotic relationship with

plantsII. 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) Includes yeast, mildew, black mold, and green mold Budding is the asexual reproduction of yeast

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)

Stipe is the stem-like structure of a mushroom

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Gills are found on the cap of the mushroom and contain the basidospores.

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 Also makes penicillin Remains dormant until conditions are right

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 associationVI. Mycorrhiza-also not a division but an association. It has a mutualistic

relationship with fungus and plants. Most Basidiomycota and some Zygomycota are involved-they

form fine thread-like hyphae around the plant roots increasing absorptive surface of the plant roots, resulting in more nutrients entering the plant, and helps with maintaining water supply in the soil. The Mycorrhiza benefits by receiving organic nutrients, like sugar and amino acids.

Some Orchids can’t survive without this symbiotic relationship.

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

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