Microbiology II

Virus replication

Only capable inside of living host cells

Viruses are:

Submicroscopic infectious microorganisms

VIruses can infect:

All life forms- humans, plants, bacteria…

When not inside a host cell, viruses exist:

As independent particle known as virons

Virions consist of:

• consist of DNA/RNA that encodes the structure of proteins that the virus needs

Caspids

• protein coat that protects the genetic material in virions

• also coats the outside envelope of lipid sometimes

How do viruses assemble and what do they form

They self-assemble, to form simple geometries of repeated protein units from helical to more complex structures

Viruses are most likely to cause

Global epidemics and pandemics, like influenza or COVID-19

DNA virus strands

dsDNA and ssDNA

DNA virus examples

Polyma, papilloma, adeno, herpes, pox, parvo (ssRNA)

RNA virus types

• +ssRNA

• -ssRNA

• dsRNA

RNA virus examples (+ssRNA)

Picorna, Noro, Toga, Flavi, Corona, Retro

RNA virus examples (-ssRNA)

Rhabdp, paramyxo, orthomyxo, bunya, filo

RNA virus examples (dsRNA)

Reo

DNA virus properties (6)

• DNA is stable

• virus replication is in nucleus

• Virus DNA packaged into preformed capsids (procapsids)

• persistent infection

• temporal regulation of protein production

• small DNA viruses depend on cellular DNA rep enzymes

RNA virus properties (5)

• RNA is unstable/labile/transient

• replication is in cytoplasm

• virus RNA co-assembles with capsid protein

• RNA prone to mutation

• ssRNA viruses need to supply RNA polymerase

A virion is:

The infectious viral particle

DNA enveloped viruses

Herpes, pox, hepadna

DNA naked capsid viruses

Parvo, polyma, papiloma, adeno

RNA enveloped viruses

• Toga, flavi, corona, retro (+RNA)

• Rhabdo, paramyxo, orthomyxo, bunya, filo (-RNA)

RNA naked capsid viruses

• reo (double capsid)

• Picorna (+RNA)

Naked capsid virus properties (3)

• protein only

• stable

• released by cell lysis

Naked capsid virus consequences (4)

• spreads easily

• survives GI passage

• resistant to dryness and detergents

• susceptible to antibodies

Enveloped virus properties (3)

• lipids, proteins, glycoproteins, membrane

• Labile/unstable

• Released by cell budding (LYSOGENIC replication)

Enveloped virus consequences (2)

• spreads through body fluids/organs

• needs more complex immune response (like delayed hypersensitivity and inflammatory factors)

2 types of virus life cycle patterns

Lytic and lysogenic

Lytic life cycle pattern

• virus is usually naked capsid

• enters cell—>undergoes transcription + translation—>once full of capsids, viral replication occurs—>cell lysis (burst)—> release capsids

Lysogenic life cycle pattern

• virus usually enveloped

• virus replicates where cell replicates

• Longer cell cycle than lytic since virus integrates into host genome (ensures virus survival)

Lytic cell cycle examples:

Common cold viruses, picorna

Lysogenic virus examples

HIV, herpes

Latency is:

The time from initial infection to time when clinical signs of infection of detectable virus appear

Acute infection example

Common cold

Acute infection, rare late complication example

Measles, SSPE

Latent infection example

Varicella-zoster

Chronic infection example

Hep B

Chronic infection, late disease example

HTLV-1 leukemia, HIV

Viral replication in an uninfected cell begins with , and is followed by ___

Begins with RECOGNITION and ATTACHMENT, followed by TRANSCRIPTION and TRANSLATION

Most antiviral meds work by:

Inhibiting viral DNA replication

DNA viruses work by:

• virions attach to cell and release capsid

• capsid releases viral DNA into nucleus

• allows for immediate expression of viral mRNA and protein synthesis (using cellular polymerases)

• DNA containing capsids go to ER, and mature in golgi before cell release

Most common DNA viruses

Adenoviruses, cytomegalovirus, Epstein-Barr virus, Hep B, Herpes 1&2, papovavirus, Varicella-Zoster virus

Herpes viruses all require:

Close contact and exchange of some bodily fluid

HSV-1 is MAINLY transmitted by ___ and causes ___

Oral-to-oral contact, and causes cold sores

HSV-2 is transmitted by ___ and causes ___

Transmitted sexually, and causes genital herpes

HSV-1 and HSV-2 are both:

Lifelong

Most oral and genital herpes infections are:

Asymptomatic

Herpes is most contagious when:

Symptoms are present (but can still be transmitted without symptoms)

Common herpes symptoms:

Painful blisters or ulcers at site of infection

After initial herpes infection ___, predisposing herpes factors are ___(2)

Virus stays dormant in trigeminal ganglia and can be reactivated later in life, factors include stress and UV light exposure

Human Papillomavirus (HPV) commonly causes:

Skin or mucous membrane growths (warts)

HPV is transmitted by ___, and in the US occurs ___

Sexually and through skin-to-skin contact, and occurs in ¼ people

Most HPV doesn’t lead to cancer, but some genital HPV has led to:

Cervical cancer

What type of cancer has been linked to HPV?

Oropharyngeal cancers

CDC recommends 11-12 years get HPV vaccine:

2 doses, 6 months apart

(vaccine helps against HPV strains most likely to cause genital warts or cervical cancer)

HPV has been linked with:

increased risk of oropharyngeal cancer and vaginal cancer

Epstein-bar virus has been linked to:

Nasopharyngeal cancer and other lymphoma (Burkitt’s)

• provides oncogenes to support cell proliferation

Viral infections are cancer causing by:

Suppressing growth cell inhibitors, favoring cell proliferation and cell division

‘Lazy‘ lysogenic cells that make cell do the proliferation (while they stay in the cell):

HPV, the virus mutates p53 which usually prevents unwanted cell proliferation

for -ssRNA virus replication:

RNA must first be transcribed with viral RNA polymerase

• -ssRNA virus are enveloped so they can bring its own RNA poly into cell

for +ssRNA replication:

protein expression occurs first

• some of the fastest virus replication

• phagocytosis releases viral RNA to form polyprotein—>cleaved polyprotein releases RNA polymerases

(ex: coronavius, norovirus, picovirus, enterovirus)

SARS-COV19 Virus transmission and symptoms:

• aerosol droplets

• (begins 2-14 days after exposure) fever, sore throat, fatigue, loss of smell/taste, shortness of breath, hypoxia and acute respiratory distress

COVID19 testing:

Viral DNA tests (RT-PCR), antibody testing, and chest CT scan

COVID-19 properties and fatalities:

• usually benign, causes common cold

• fatalities increase with age, and in those with underlying conditions (obesity, diabetes, hypertension, smoking)

Bacteriophages are:

VERY common viruses that attack bacteria using a sophisticated structure (very specific)

All kingdom animalia are common in that:

They are organisms lacking cell walls (including parasites)

Fungal kingdom is characterized by:

Chitin containing cell walls

Stramenopila kingdom characterized by:

Single and multi celled eukaryotes with rigid cell walls capable of photosynthesis (like algae)

Protists are:

Protozoa, stramenopila, fungi

Archaea characteristics: (4)

• unusual habitats

• ether-based lipids (phytanol)

• characteristic RNA

• no peptidoglycan

3 big groups of archaea

• halophiles

• thermoacidophiles

• methanogens

Prions are:

• slow viruses

• long incubation time (can be over decades)

Prion virus characteristics:

• protein-containing

• HIGHLY resistant to heat inactivation, formaldehyde and UV light to inactivate viruses

• INACTIVATED by: protein and lipid disrupting agents (phenol, ether, NaOH)’neurodegenerative, cause abnormally folded protein in brain

Prion replication properties: (2)

• resistant to degradation

• reshapes normal protein into abnormal protein

Human and animal prion disease examples:

• Human: Kuru, Creutzfeld-Jakob

• Animal: Scrapie, Mad Cow Disease

Prevent prion disease:

• proper eating and handling of contaminated tissues

• contaminated neurosurgical instruments

• no treatment, can be genetically passed down

Helminth parasitic infections properties:

• includes: nematodes, trematodes, and cestodes (round, fluke, and tape worms resp.)

• worms cause chronic eosinophilic inflammation (IgE)

• Fecal transmission route

Helminth parasitic infection problem:

• very large global health problem (esp in unsanitary areas)

• worms accumulate immune cells without elimination—>tissue damage

• worms stay in intestines or in tissue to avoid immune response

Protozoan infection properties:

• single-celled organisms found in nature, oral cavity, and intestinal tract

• most are harmless (commensals), only a few cause disease

2 types of protozoan infections and common transmission

• Intestinal: cause diarrhea and GI disease

• Intracellular: live in host cell and affect blood and bone marrow cells

• transmitted with fecal-oral route (contaminated water)

Protozoan infection treatment targets:

Thymidine synthesis-interferes with DNA production

Fungi are:

neither plant nor animal

Oral candidiasis properties: (3)

• common oral fungal infection

• nosocomial infection

• acquired in medical settings

Fungal cell structure:

• like animal cells with a cell wall made of chitin, glucans, and mannans

• also have cell membrane of ergosterol

Name the 3 components of the fungal cell wall

(out to in)

• mannan

• beta-glucan

• chitin

Predominant exposed sugar in fungi

Mannan

Human vs fungi glucans

• differ in type of glycosidic bond

• humans: beta 1,3 or beta 1,4 glycosidic bond

• fungi: 1,6 glycosidic bond and beta 1,3 linkages

• (one approach to control fungi infections-inhibit beta-1,3-glucan synthase)

Chitin properties:

• characteristic in fungi

• a linear carb of 2000 repeated units of N-acetylglucosamine, joined with beta 1,4 linkages

• human equivalent= hyaluronic acid

2 groups of fungi

yeasts and molds

Yeast properties: (3)

• single-celled

• repro with budding or fission (grow in liquid or on surfaces)

• forms discrete, pasty colonies

Mold properties: (3)

• multicellular

• thread-like tubular structures

• forms mycelium (a mat) (can be very elaborate)

3 methods of yeast reproduction:

• nuclear fission

• budding

• germ tube

various sexual structures made by molds to identify a fungi

Phenotype switching allows fungus to:

Evade host immune response (become more pathogenic)

Phenotype switching is:

Change morphology in response to environment change

ex: candida albicans can switch from yeast to hyphae depending on temperature

Aspergillus fungi producing dangerous toxins

• toxins associated with food: wheat, sugar, grains, corn

• cause: kidney and liver damage, seizure, coma, death (more severe with allergic reaction)

Proteases are:

Enzymes that break down proteins on host cell surfaces

Phospholipases are:

Enzymes that break down phospholipids of host cell membrane

Proteolytic enzymes damage host’s:

Inter-epithelial junction resulting in host damage and fungal invasion

• enzyme release (protease and phospholipase) is key in virulence of C. albicans

Candida albicans characteristics:

• common commensal fungi in oral cavity

• pathogenic with opportunistic infection:

  • weakened immunity: old people, infants, HIV, diabetes, PROLONGED USE OF ANTIBIOTICS AND CORTICOSTEROIDS

• common among denture patients

• commonly present on palate, tongue, buccal vestibules and lip commissures

Common causes of nosocomial infections: (3)

• catheters and hemodialysis ports

• chemotherapy

• antibiotic use

Fungi can cause systemic infections like:

Aspergillosis and histoplasmosis