Fill in the blanks:

Lymphoid tissue and structures such as _____ and _____ are collectively called gut-associated lymphoid tissue.

• stomach acid eliminates many microbes
• rapid movement of food
• paneth cells

• mostly anaerobes and facultative anaerobes
• most of these microbes are known as enteric bacteria - gram (-) rods that are facultative anaerobes

• effective sanitarium practices in food production, handling, storage
• modern methods of sewage treatment
• disinfection of water

• infection: incubation time 12 hrs. - 2 weeks
• Intoxication: incubation time 1-48 hrs. after ingestion

• thoroughly cook foods to a temperature high enough to kill bacteria
• foods should not be allowed to remain in the danger zone for more than 2 hours (39-140 degrees F)
• utensils should be cleaned thoroughly
• cutting boards: avoid cross-contamination
• proper hand washing

• etiology: caused by Shigella; 4 species - S sonnei, S dysenteriae, S flexneri, S boydii; facultatively anaerobic nonmotile gram (-) rod; closely related to pathogenic E coli
• mode of transmission: spread only from person to person; no natural reservoir in animals
• Signs/Symptoms: fever, abdominal cramps, diarrhea (sometimes with bloody mucus); Shigellosis can cause up to 20 bowel movements in one day
• Incubation period: 12 hrs. to 2 weeks
• epidemiology: in US most cases are caused by S sonnei and affect children under 5

1. type 3 secretion system
2. enterotoxins that trigger loss of electrolytes and water (similar to cholera toxin)
3. S dysenteriae secretes shiga toxin, which is an exotoxin that inhibits normal functioning of the host ribosome (can result in ulceration of the intestinal mucosa)

• facultatively anaerobic peritrichous gram (-) rod
• 2 species: S enterica and S bongori (most cases are cause by S enterica)
• habitat is the intestinal tracts of humans and virtually all vertebrates
• serotype typhi (causes typhoid fever) and is only found in humans

1. transmission mode: person-person, animal-person via the fecal-oral route; poultry, chicken, eggs, ground beef, fruit; sometimes direct transmission from animals (ex. pet reptiles)
2. incubation time: 12-36 hours
3. signs/symptoms: fever, nausea, abdominal pain, diarrhea (usually not bloody)
4. treatment/prevention: recovery usually complete in a few days, but many patients shed the organism in feces for up to 6 months; antibiotic therapy is not useful in treating salmonellosis; bacteria are generally destroyed by normal cooking
5. epidemiology: mortality less than 1%, but death rate is higher in infants and the very old (death is usually from septic shock)

1. etiology: serotype Typhi causes typhoid fever
2. Incubation period: 2-3 weeks
3. transmission mode: not found in animals, only spread by ingesting food or water contaminated with feces from humans
4. symptoms/signs: high fever, continual headache, loss of appetite, sometimes a rash, diarrhea appears after 2nd or 3rd week, then fever starts to decline; In severe cases, ulceration and perforation of the intestinal wall can occur, allowing bacteria to enter the abdominal cavity.
5. epidemiology: mortality w/treatment (abx therapy) less than 1%; w/o treatment 12-30% of patients die

• Typhoid fever is systemic - serotype typhi are able to multiple within macrophages and are disseminated via circulation to multiple organs, especially the spleen or liver
• 1-3% of recovered patients become chronic carriers
• Typhoid Mary harbored the salmonella in her gallbladder and shedding the disease in her feces
• Fluoroquinone or ceftriaxone for MDR strains
• treatment to end the carrier state involves 4 weeks of abx therapy
• recovery confers life long immunity

• transmission via the fecal-oral route
• diarrhea (often bloody) appears 24-72 hours after consumption of bacteria
• infectious dose likely around 10 cells (very acid-tolerant)
• illness from ingestion of contaminated raw leafy vegetables and under cooked meat
• main reservoir is cattle which are not affected by it
• vegetables and fruits can be contaminated during heavu rains, waste from cattle farms can easily wash into nearby crop fields

Fill in the blanks:

Shigella E coli invade the _____.  Enterohemorrhagic E coli releases the toxin into the _____.

• expresses Shiga toxin a prophage gene
• inhibits protein synthesis by targeting 28s ribosomal RNA
• can cause inflammation and bleeding of the colon
• antimicrobial drugs induce this strain to increase its production of shiga toxin, worsening the disease
• uses type 3 secretion system - a molecular syringe embedded in the membrane that directly injects virulence proteins into the host cytoplasm
• disrupts normal host cell signaling pathways
• causes actin-driven rearrangments that cause the host cell to build a pedastal on which the E. coli can perch - this helps prevent engulfment
• in HUS the tiny filter units in the kidneys known as glomeruli become clogged with platelets and damaged red blood cells
• this leads to problems with the kidneys ability to filter and eliminate waste products

• caused by vibrio cholera
• slightly curved gram (-) rod
• found in marine environments - preferring warm, salty, alkaline water (often in association with crustacean copepods and particulate matter)
• survives in both salt and freshwater

• Ingestion of contaminated water or raw/under cooked  seafood
• Incubation period: usually 2-3 days
• Most important virulence factor: cholera toxin (plasmid-encoded)
• Characterized by “rice-water” diarrhea, vomiting, muscle cramping, sunken eyes, rapid yet diminished pulse. Leads to severe fluid and electrolyte loss which results in dehydration, kidney failure, coma, death; acidosis - due to loss of bicarbonate ions; hypovolemic - caused by reduced blood volume; thirst, metabolic acidosis, hupokalemia, and hypovolemic shock
  
• Mortality rate is 25-50% in untreated patients. Reduced to 1% with treatment (doxycycline and fluid and electrolyte replacement).

1. AB5 toxin: composed of an enzymatic A subunits and B subunits (B=receptor binding)
2. B subunits bind to host cell receptor (ganglioside)
3. entire toxin is endocytosed
4. A subunit is released -> activates an enzyme called adenylate cyclase -> results in increased cAMP -> causes efflux of electrolytes -> water follows via osmosis leading to diarrhea

• etiology: gram (-) spiral-shaped microaerophiloc bacterium
• disease associated: responsible for most cases of peptic ulcer disease -> ulcers are erosion's of the lining of the stomach or duodenum
• epidemiology: 30-50% of the population in the developed world become infected; infection rate is higher elsewhere; only about 15% of infected individuals develop ulcers; gastric cancer develops in 3% of infected individuals
• H. pylori can survive the highly acidic environment of the stomach by producing urease, which converts urea to ammonia (which is alkaline) - this neutralizes stomach acid
• Virulence: flagella enable burrowing through stomach lining; adhesins facilitate attachment to gastric cells

• eukaryotic
• aerobic or facultatively anaerobic
• contain cell walls made of chitin
• chemoheterotrophic - secrete catabolic enzymes and acquire nutrients by absorption
• most are decomposers
• live as unicellular yeasts and/or molds

• fungi are eukaryotic and bacteria are prokaryotic
• the cell membrane of fungi have sterols while bacteria do not have sterols except in mycoplasma
• the cell wall of fungi have glucans, mannans, and chitins, while the bacteria cell wall has peptidoglycan
• Fungi produce a wide variety of sexual and asexual reproductive spores, while bacteria have endospores and some asexual reproductive spores
• Fungi are limited to heterotrophic, aerobic, and facultatively anaerobic, while bacteria are heterotrophic, chemoautotrophic, photoautotrophic, aerobic, facultatively anaerobic, and anaerobic
• Fungi are often sensitive to polyenes, imidazoles, and griseofulvin while bacteria are often sensitive to penicillins, tetracyclines, and aminoglycosides

• grow better in an environment with pH~5 which allows them to grow on bathroom walls, shoe leather, and newspaper
• more resistant to osmotic pressure than bacteria
• can grow on substances with a very low moisture content
• often capable of metabolizing complex carbohydrates that bacteria are not able to break down

• there are two basic body shapes: molds are composed of long filaments called hyphae, either septate or aseptate, can bear reproductive spores, hyphae grow to form a filamentous mass called a mycelium; yeasts are nonfilamentous, unicellular fungi that are spherical or oval
• some fungi are dimorphic which means they can produce both yeast-like and mold-like shapes; generally the yeast form causes diseases, whereas the filamentous form does not; in pathogenic fungi it is temperature-dependent --> 37 degress C = yeast like and 25 degrees C = mold like

• Asexual Reproduction: fungi produce lightweight spores that disperse over large distances; fungi can reproduce asexually by fragmentation of their hyphae
• sexual reproduction: occurs in 4 basic steps - haploid (n) cells from fungi or different mating types fuse to form a dikaryon which is neither haploid  or diploid, just n+n.  a pair on nuclei within a dikaryon fuse to form one diploid (2n) nucleus,  meiosis of the diploid (2n) nucleus restores the haploid state (2). the haploid nuclei are partitioned into spores of different mating types, which are disseminated into the environment.

Fill in the blanks:

1. _____: sporangiospores form inside a sac called a sporangium which is borne on a stalk called a sporangiophore at either the tips or the sides of the hyphae
2. _____: form a thickened cell wall inside hyphae
3. _____: are produced at the tips and sides of hyphae but not within a sac

1. Asexual spores: sporangiospores form inside a sac called a sporangium which is borne on a stalk called a sporangiophore at either the tips or the sides of the hyphae.

2. Chlamydospores form a thickened cell wall inside hyphae

3. Conidia are produced at the tips and sides of hyphae but not within a sac

• most common fungal infections
• confined to hair, nails, outer layers of skin
• acquired by direct contact with hyphae or spores of fungi

• fungi that colonize the hair, nails, and the outer layer of the epidermis - dermatophytes
• dermatophytes can trigger immune responses that can damage deeper tissues (unlike superficial infections)
• Epidermophyton, trichophyton, and microsporum cause the majority of dermatophytic infections
• deramtophytes grow on keratin
• moisture favors fungal infections
• transmitted by direct ad indirect contact
• dermatophytes are among the few contagious fungi
• dermatophytes are classified by natural habitat

Fill in the blank:

• Tinea Capitis - _____
• Tinea Cruris - _____
• Tinea Pedis - _____
• Tinea Unguium - _____

• Tinea capitis (ringworm of the scalp)
• Tinea cruris (ringworm of the groin/jock itch)
• Tinea pedis (ringworm of the foot/athlete’s foot)
• Tinea unguium (ringworm of the nails)

• overgrowth of candida albicans which is an oportunistic yeast that is a common member of microbiota of skin and mucous membranes
• causes thrush (oral), skin, and vaginal infections if it enters the bloodstream it can travel to the heart, central nervous system, eyes, and bones
• risk factors include immunosupression, broad spectrum abx., obesity and diabetes.
• Candidiasis can be cutaneous, hepatic, nail infection

• manifests as white coating in the mouth, resembling cottage cheese
• common in newborns and immunocompromised individuals; also occurs following abx. therapy
• treatment - topical treatment (oral spray or swab) with a nystatin solution (nystatin binds to ergosterol and forms pores in the membrane)

An overgrowth problem: Candida overgrows if vaginal pH becomes alkaline or normal microbial populations are reduced. 

Review: bacterial microbiota of mucous membranes in the genitourinary tract and mouth normally suppress the growth of Candida albicans

• risk factors: critical illness, hospitalization/live in a healthcare facility, diabetes, organ transplant, cancer chemotherapy, and taking broad-spectrum abx
• signs of candidemia include fever and chills that do not improve with antibiotics, and symptoms/signs of septic shock

• fungi produce spores that are disseminated through the air and can be transmitted through inhalation
• spores may germinate in the lower respiratory tract
• rate of fungal infections of the lower respiratory system has been increasing
• opportunistic infections
• risk factors - immunosuppressed patients, AIDs, transplant drugs, anticancer drugs

• histoplasmosis
• coccidioidomycosis
• pneumocystic pneumonia
• blastomycosis
• aspergillosis

• caused by histoplasma capsulatum which is a dimorphic fungus that survives and replicates intracellularly in macrophages
• signs and symptoms include: asymptomatic in most cases; symptomatic infection causes coughing with bloody sputum, fever, aches/pains, or skin lesions
• humans inhale airborne spores from the soil, especially where droppings from birds and bats have accumulated (droppings provide nutrients, especially nitrogen, for the fubgus)
• lungs are initially infected but macrophages can carry spores through blood and lymph becoming systemic (this is rare)
• In tissue growth it is yeast-like and in soil or artificial media it is filamentous mycelia

• etiologic agent: Coccidioides immitis which is a dimorphic fungus.  In tissues it forms a thick-walled body called a spherule filled with spores.  In soil-filametous, and wind carries arthroconidia to transmit the infection
• found in dry, alkaline soils, such as in the southwest-frequent occurrence in San Joaquin Valley
• most infections not apparent-a systemic disease, progressive disease resembling TB disseminates through body
• symptoms can include chest pain, fever, coughing, weight loss

• motile by means of cilia, flagella, and/or pseudopods (except for subgroup apicomplexans)
• require moist environments
• mostly aerobic heterotrophs
• most only reproduce asexually
• free-living and pathogenic protozoa exist as a trophozite (feeding and growing stage)
• many have a hardy resting stage called a cyst-cyts are not reproductive structures they have a thick capsule and low metabolic rate.  One trophozite forms one cyst which later becomes one trophozoite

• caused by giardia intestinalis (AKA giardia lamblia)
• flagellated protozoan
• two forms: trophozoite which  are motile and can attach firmly to intestinal wall using ventral adhesive disk.  Cyst which are dormant and resistant to chlorine, heat, dessication stomach
• symptoms/signs: greasy, frothy, fatty diarrhea, malaise, nausea, weakness, weight loss, abdominal cramps, odor of hydrogen sulfide on breath or stools
• diplomonad (2 identical nuclei)
• no mitochondria
• infective dose as few as ten cysts

• mode of transmission: fecal-oral, usually from ingesting cysts from contaminated water, also contaminated food or hands; pathogen is shed in feces of humans and animals
• hikers, campers, swimmers, and daycare workers are at particular risk
• diagnosis and treatment: microscopic examination to reveal trophozoites and cysts in feces, treatment with metronidazole is usually effective within a week
• incubation period is 3-25 days

• caused by trichomonas vaginalis; anarobic flagellated protozoan
• usually sexual transmitted
• typically symptomatic in women and asymptomatic in men; in women it causes profuse frothy greenish discharge with a foul odor, irritation and itching, pain during urination and sex
• normal vaginal lactobacilli keep trichomonas in check; if normal acidity of vagina is disturbed, overgrowth may occur
• no cyst stage-must be transferred quickly from host to host before dessication occurs
• treatment-metronidazole
• no mitochondria
• undulating membrane-a membrane bordered by a flagellum
• can infect babies during passage through birth canal, which can result in preterm delivery and low birth weight of a baby
• incubation period is 4-28 days
• often accompanied by coinfection with gonorrhea

• protozoan disease that affects the nervous system: it is caused by trypanosoma brucei (a flagellated protozoan)
• spread by tsetse fly vectors
• victims become so tired they stop eating, succumb to coma and death, rapid mood swings and confusion
• T. brucei gambiense is the most common form and the only reservoir is humans
• incubation period is a few weeks or months
• T. brucei rhodesiense-rservoir domestic livestock and many wild animals; incubation period is a few days; death occurs within weeks, sometimes from cardiac problems before CNS is affected

• site if bite becomes lesion
• parasites in the blood create fever, lymph node swelling, and headache
• protozoa invade CNS, causing meningoencephalitis; headache, extreme drowsiness, abnormal neurological function

• diagnosed by microscopic observation of trypanosomes in blood, lymph, spinal fluid, or tissue biopsy
• treatment based on disease stage-untreated african sleeping sickness is fatal
• insecticide application and large scale release of sterile male tsetse flies helps reduce occurrence
• eflornithine crosses the BBB and blocks an enzyme required for proliferation of parasite-treatment is toxic; tsetse flies attracted to the color blue

The vegetative, reproducing, feeding state of a protozoan is called a:

A. cyst

B. trophozoite

C. spore

D. hyphae

• caused by four species of plasmodium: P. falciparum, P. vivax, P. ovale, and P. malariae
• epidemiology: endemic throughout tropics and subtropics; affects % of the world's population; malaria causes 500,000-1 million deaths annually
• vector transmission: anopheles mosquito
• symptoms associated with parasite's life in erythrocytes: recurrent fever + chills, diarrhea, vomiting, severe headache; occasional pulmonary or cardiac dysfunction, jaundice may occur; anemia, weakness, and fatigue gradually occur
• survivors acquire a limited immunity

1. viral DNA enters the cell as in the lytic cycle, but the host cell's DNA is not destroyed.  The phage's genome does not immediately assume control of the cell.
2. viral DNA is incorporated into the host chromosome, and remains inactive as prophage.
3. the host cell resumes normal function, but when it replicates its genome, the viral DNA will be replicated as well.  Daughter cells will acquire the prop[hage.  Prophage may remain part of chromosomes for generations or forever.
4. eventually, the prophage may be excised from the chromosome (called induction), and now the lytic cycle can begin.

• One result of lysogeny is the host cell may exhibit new properties.  E.coli 0157:h7: the gene that codes for Shiga toxin is a prophage gene.  Only Streptococci carrying a lysogenic phage are capable of causing toxic shock syndrome.
• Another result is specialized transduction.  Any bacterial gene could be packaged in a phage capsid.  In specialized transduction, only certain genes can be transferred.

Herpesvirus

• enveloped with icosahedral capsid.  Envelop comes from nuclear membrane.  dsDNA genome - diameter is 120-300 nanometers
• HSV1 causes the majority of cold sores.  It is transmittd through oral secretions and usually remains latent in the trigeminal nerve ganglia, this is the nerve that links the CNS and face.  Herpetic whitlow-abrashions in skin result in HSV1 infection.
• HSV2 causes the majority of genital herpes and is transmitted via sexual contact and remains latent in the sacral nerve ganglia.
• recurrence can be triggered by stress, fever, hormonal changes, UV light, immunosuppression
• HHV3 is responsible for chicken pox and shingles

• caused by herpesvirus varicellovirus (HHV-3)
• mode of transmission is inhalation of infected particles from skin lesions
• latency occurs when the virus enters the peripheral nerves and moves to a dorsal root ganglion near the spine where it persists as viral DNA indefinitely
• antibodies cannot penetrate into the nerve cell, and because no viral antigens are expressed on the surface of the nerve cell, cytotoxic T cells are not activated
• later in life (due to stress or immunosuppression), the latent virus becomes activated, causing shingles
• in shingles, viruses move along peripheral nerves to the cutaneous sensory nerves of the skin
• shingles is a different expression of the virus that causes chicken pox because the patient now has partial immunity to the virus

• The effectiveness of the varicella vaccine declines with time, so varicella in previously vaccinated persons (breakthrough varicella) is fairly common. This is an issue for adults (disease is more severe) so everyone over 60 should get zoster vaccine.

Human Papillomavirus

• small non-enveloped icosahedral viruses; ds DNA genome with a diameter of 55 nannometers
• papillomaviruses cause warts which are growths of the epithelium of the skin on face, trunk, hands, feet, elbows, knees, or genitalia; this virus causes infected epithelial cells to divide rapidly; it is transmitted via direct and indirect contact and is highly infectious
• there are more than 100 strains of HPV; some strains cause cancer-HPV integrates into the genome and transforms cells which increases expression of viral oncogenes E6 and E7 which inhibit tumor suppressor genes; In oncogenic retroviruses, a provirus can convert the host cell into a tumor cell.

A defining feature of all oncogenic viruses is that their genetic material integrates into the host cell’s DNA and replicates along with the host cell’s chromosome.

• RNA viruses do not integrate into the host genome, except for HIV
• herpesvirus and papillomavirus are latent viruses that become integrated into the chromsomes and cannot be excised

• enveloped +ssRNA viruses
• genus includes west nile virus, dengue virus, yellow fever, virus and zika virus

• transmitted by mosquitos
• reservoir - birds
• most people infected with virus do not develop disease, those who do have flu-like illness
• can occasionally cross blood brain barrier and cause encephalitis - headache, high fever, neck stiffness, disorientation, coma, convulsions, paralysis, neurological effects may be permanent and death may occur

• transmission - infection occurs primarily through inhalation of airborne viruses released by coughing or sneezing; self inoculation - transfer viruses on fingers to nose or mouth
• signs/symptoms - sore throat, congestion, cough, muscle aches; sudden flu distinguishes flu from a common cold
• lower respiratory illness; influenza can remain invective for up to 8 hours on objects outside the body; incubation period of one day; symptoms produced by immune response

• HA and NA are glycoprotein spikes found on the surface of the virus

Hemagglutinin: (HA) Allows virus to bind to host cells and trigger endocytosis. Facilitates entry of viral genome into host cell.

• infuenza steals the host cellular 5' mRNA cap
• RNA - dependent RNA polymerase transcribes mRNA from template (-) RNA genome; viral mRNA will be capped at 5' end like cellular mRNA; virus enzyme removes cellular 5' cap, puts it onto ends of viral mRNAs
• influenza "pirated cap" provides translation advantage; (+) mRNA serves also as template to make (-) genomes for new virus progeny[image]

• Accumulation of hemagglutinin and neuriminidase gene mutations within a single strain of virus in a given geographic area. (Basically, a slow change in the antigens on the viral surface over time)

• The RNA-dependent RNA polymerase does not have a proofreading function. This is crucial to the virus’s evolutionary strategy! Changes in the sequences encoding surface antigens leads to evasion of the immune response!
• this is why you need to get a vaccine every year

• genus of parasitic protozoa
• apicomplexan: characterized by schizogony which is a form of asexual reproduction
• complex life cycle involving stages in the host and vector (anopheles mosquito)

• sporozoites: injected into host's blood from mosquito and undergo schizogony in liver cells and produce merozoites
• merozoites: infect RBCs
• trophozoites: grow in RBCs, produce more merozoites via schizogony; RBCs rupture, releasing merozoites which infect more RBCs
• some merozoites develop into male and female gametocytes, which are taken up by the mosquito
• (life cycle in mosquito: gametocytes --> zygote --> ookinete --> oocyst --> sporozoites --> cycle begins again)

• reproductive cycle occurs within RBCs-hides parasite from immune surveillance (RBCs don't display MHC)
• adhesins allow red blood cells to adhere to certain tissues (avoid clearance by spleen)
• changes in body chemistry attract other mosquitos: gametocytes trigger changes in body odor that attracts anopheles mosquitoes

• diagnosis made by identifying plasmodium in blood
• treated with various antimalarial drugs
• some plasmodium strains are resistant to antimalarial drugs
• prevention requires control mosquitoes; use of mosquito nets is important way to reduce contact

• In RBCs, plasmodium digests hemoglobin, which releases free heme
• Free heme is toxic.  So the parasites covert it into a non-toxic insoluble crystalline form called hemozoin
• many anti-malarials (ex. Chloroquine) work by inhibiting hemozoin formation
• hemoglobin is necessary for parasite's development, but it is not known which component specifically is required; digests it and produces hemozoin as a byproduct; detoxification through biocrystallization

• multicellular eukaryotic animals
• platyhelminths: flatworms
• nematodes: roundworms

• may lack a digestive system
• nervous system is reduced
• means of locomotion is often reduced or lacking
• reproductive system is often complex

• larval stage
• adult
• eggs

• whipworm: trichuris trichiura; adults form in intestine and burrow into the intestinal wall; heavily infected individuals can experience dysentery, loss of muscle tone, prolapsed rectum
• pinworm: enterobius vermicularis; migrates out of anus to lay eggs, causing itching; transmitted from hands, contaminated bedding and sexually
• Loaisis (african eye worm): loa loa; transmitted through bite of deer fly
• lymphatic filariasis (elephantiasis): wuchereria bancrofti; transmitted  through bite of mosquito; presence of adult worms in lymphatic system results in obstruction; lymph accumulates behind the blockage

• tapeworm is the common name for cestode, it is a flat, segmented, intestinal parasite and it can be  meters long>

• usually asymptomatic
• nausea, abdominal pain, weight loss, and diarrhea may occur
• people usually don't know they are infected until they pass segments of the helminths

• taenia saginata: beef tapeworm
• taenia solium: pork tapeworm

• cuticle = outer surface (steals host nutrients by absorption)
• scolex = suckers/hooks attach to host tissue
• neck = behind scolex; segments called proglottids originate here; new proglottids grow from neck
• proglottids mature as they are pushed from neck, producing male and female reproductive organs; each proglottid has both sex organs and may fertilize other proglottids of the same or different tapeworms
• after fertilization, proglottids furthest from neck become gravid (full of fertilized eggs); they break off the chain and pass out of the intestine in feces

• viruses are nucleic acid (DNA or RNA) wrapped in a protein coat; some also have a lipid membrane; envelope
• viruses are NOT cells
• infectious agents having either DNA or RNA (never both); single stranded or double stranded
• cause of infections of humans, animals, plants, and bacteria
• cannot carry out any metabolic pathway or reproduce imdependently
• are very small
• hijack the host cell's machinery in order to replicate
• no cytoplasmic membrane, cytosol, organelles

• pro: viral envelope provides some protection from immune system
• con: enveloped viruses are more fragile than naked viruses; more susceptible to detergents, alcohol, dessication

• pro: capsid of a naked virus is more stable outside the host, and protects the nucleic acid from nucleases in biological fluids
• cons: exposes more viral proteins; more susceptible to recognition by immune system

• extracellular state: called virion; protein coat (capsid) surrounding nucleic acid; some have phospholipid envelope; outermost layer provides protection and recognition sites for host cells
• intracellular state: capsid removed; virus exists as nucleic acid

Fill in the blanks:

Animal viruses bind to _____.  People who lack the _____ for parvovirus B19 are resistant to infection and don't get _____.

1. attachment (absorption) - proteins on the virus recognizes receptor proteins on the surface of the host's cell wall.  The virus attaches to the host cell.
2. Entry - the virus releases lysozyme to degrade the peptidoglycan of the cell wall.  The phage's tail contracts, forcing a hollow tube through the cell wall/membrane.  The virus injects its genome through the tube.  Viral enzymes (either carried in the capsid or coded by the viral genes and made by the bacterium) degrade bacterial DNA.
3. Synthesis - new viruses are synthesized - viral nucleic acid is transcribed and translated by the bacterial host, resulting in viral nucleic acid and protein that will be assembled into new virus particles.
4. Assembly - viral nucleic acid is packaged into capsids.  Sometimes, host DNA is "accidentally" packaged into capsids - now when the virus infects a new host, it will inject the old host's DNA into the new host (transduction).
5. Release - newly assembled viruses are released, and the cell lyses open.

• attachment of an animal virus depends on binding of virion proteins to protien/glycoprotein receptors in animal cell's cytoplasmic membrane
• animal viruses lack tails and tail fibers - they have glycoprotein spikes or other attachment molecules on their capsids or envelopes
• viruses enter host cell via one of the mechanisms on the next slide

• Replicate DNA in the nucleus of the host cell using host enzymes or viral enzymes (depending on species).  Genes can be transcribed directly bu host RNA polymerase in nucleus
• Synthesize capsomeres and other proteins in the cytoplasm using host enzymes
• The capsomere proteins migrate into the nucleus and are joined with newly synthesized DNA to form virions (so assembly happens in the nucleus)
• Then virions are released from nucleus into cytosol
• Examples include: herpesvirus, papvaviruses, adenoviruses, and hepadniviruses
• ds DNA - make own DNA pol or use that of the host.  Genes can be transcribed directly by host RNA pol or one encoded by viral genome
• ss DNA - require host DNA pol to generate complementary DNA strand or ss DNA of parvovirus folds back on itself to form a hairpin loop that acts as double stranded DNA

• There are 4 types: + ssRNA, -ssRNA, dsRNA, and retroviruses
• +ssRNA: positive-sense single-stranded RNA.  The RNA genome can serve directly as mRNA.  Replication of the RNA genome requires synthesis of a template (-) strand (by virally coded RNA polymerase).  The progeny (+) strands are replicated from the (-) template.  Transcription of RNA to RNA is unique to viruses - cells do not do this.
• -ssRNA: negative-sense single-stranded RNA.  The complement of the genome serves as mRNA.  Packages a viral RNA-dependent RNA transcriptase to make (+) strand, which can be translated.  Then it uses the (+) strand as a template to make (-) strand to package in virions
• dsRNA: double-stranded RNA (+) strand serves as mRNA.  Each strand of the dsRNA acts as template for transcription of its opposite using viral RNA polymerase
• retroviruses: type pf +ssRNA virus, but they do not us the (+) strand as mRNA.  The (+) strand is reverse-transcribed into dsDNA using an enzyme called reverse transcriptase.
• most RNA viruses develop solely in the cytosol
• +ssRNA: ex. polioviruse, ribosomes can translate polypeptides using the codons of such RNA
• -ssRNA: influenza, rabies
• -dsRNA: rotavirus - diarrhea in infants
• -most DNA viruses assemble in and are released from the nucleus in the cytosol.  Most RNA viruses develop solely in the cytoplasm

Fill in the blank:

Once components of animal viruses are synthesized, they are assembled into _____ and are released from the _____.

tremtodes

cestodes

Describe the role of Streptococcus mutans in dental caries in detail (including risk factors and howit degrades enamel). Can this bacteria alone cause cavities? Why or why not?

S. mutans attaches to the tooth.  S. mutans synthesizes dextran – a polysaccharide that is an important factor in formation of dental plques.  No it can not cause cavities alone, sucrose is needed.  Sucrose is hydrolyzed into fructose and glucose. The glucose is assembled into dextran.  The residual fructose is the primary sugar fermented into lactic acid,

which breaks down the enamel of teeth

Given that S. mutans is contagious, especially between adults and children,

how can parents prevent their children from getting a S. mutans infection (thereby

reducing their risk of cavities)?

You go out for dinner, and about an hour later you have abdominal cramps,

nausea and diarrhea. What most likely caused your illness?

diseases of the digestive system are often transmitted by the “oral-fecal”

route. What does “oral-fecal” route mean? How can this cycle of transmission be broken?