Chapter 13: Virus and Prions Flashcards
Characteristics of viruses
-Obligate intracellular parasites that multiply in a living host
-Noncellular, filterable (can pass through bacteriological filter) agents
-Single type of nucleic acid ( (single type- some are DNA, some are RNA) surrounded by protein coat (capsid)
-Sensitive to interferons
Viral structure: virion
-ByMorphology (discovered through e- microscopy): helical viruses
-Hollow cylinder
-Coiled nucleic acid
-No envelope
-Enveloped helical virus
-Influenza virus
-Cylinder
-Morphology: polyhedral (Icosahedral) viruses
-Icosahedral capsid
-Many sided
-Morphology: complex viruses
-Bacteriophage
-Infects bacteria
-Tail fibers- adhere to receptor on bacterial cell
-Smallpox
-Contain several protein coats/capsids or undefined capsid/missing parts of capsid
Classification of viruses
-Herpesviridae (family)
-Herpesvirus
-Human herpes virus 1, HHV 2, HHV 3
-Retroviridae
-Lentivirus
-Human immunodeficiency Virus 1, HIV 2
Viral size
-Very small
-Smaller than diameter of RBC
-Seen w/ E- microscope
Growing bacteriophages
-Phages from plaques on a lawn of bacteria
-Called PFU’s- plaque forming unit
-Tryptic soy broth
-24hrs at 37 degrees celsius
-Clearings in lawn of bacterial growth
-Bacteria being lysed
Growing animal viruses
-Why are embryonated eggs used? (growing animal viruses)
-Inexpensive
-Multiple inoculation sites
-How influenza virus used to be grown for vaccine
-Cell (tissue) culture
-Animal and plant viruses may be grown in cell culture
1) a tissue is treated w/ enzymes to separate the cells
2) cells are suspended in culture medium
-Liquid nutrient
-plastic/glass dish
3) normal cells or primary cells grow in a monolayer across the plastic container.
-1 wk
Viral identification: cytopathic effect of viruses
-Visible effect or change in cells due to viral infections, that may result in host cell damage or death
-Infected cells: changes
-Cell fusion: cells moving closer together and fusion
-Nuclear changes (larger)
-Cell lysis
-Rounding up of cells
Viral identification: tests
-serology: direct or indirect (ELISA)
-DNA/RNA probes
-PCR-rapid test
-fluorescent antibody staining
Phage replication
-Lytic cycle- phage (when infecting cell) causes lysis and death of host cell
-Lysogenic cycle- Prophage DNA incorporated in host DNA (inserts it’s DNA into host’s DNA)
Multiplication of T-even bacteriophages (lytic cycle)
Chooses cycle if exposed to UV light or mutagens
1) Attachment
-DNA + sheath + tail fibers- attach to a receptor on bacterial cell wall
2) Penetration (entry)
-Phage/lysozyme- breaks down bacterial cell wall
-Sheath contracts and injects phage’s DNA into bacterial host’s cell
3) Biosynthesis
-Where replication occurs
1Production of viral parts
4) Maturation (assembly)
-Virion- Complete viral infectious particle
5) Release
-Lysozyme breaks down cell wall- lysed
-Virions free
-Can now infect other bacteria
Specialized transduction
-Contributes to some of antimicrobial drug resistance
-A special gene is being transferred from donor to host by means of a prophage
Multiplication of animal viruses
1) Attachment- viruses (may include spikes to help in adhere) attaches to cell membrane (where receptors (protein) are located)
2) Penetration (entry)- Entry by endocytosis (via a vescicle) or fusion
3) Uncoating- Enzymatic rem of capsid
-Not see w/ phages
-Unique to animal viruses
4) Biosynthesis- production of nucleic (viral) acid and proteins
5) Maturation (Assembly)- Nucleic acid and capsid proteins assemble into virion
6) Release- by budding (usually enveloped viruses) or rupture (usually naked viruses)
Viral entry (animal viruses): Penetration by fusion
enveloped viruses entering host cells by fusing their viral membrane with the host cell membrane, allowing the viral contents to enter the cell
-Envelope of viruses fuses w/ the host cell membrane
-Entrance by fusion
-After entrance, capsid is removed
Viral entry (animal virus): Penetration by endocytosis
process where the cell membrane engulfs the virus, to penetrate the cell.
-Ex. Herpes simplex virus
-Forms vesicle around virus
Animal virus: Release of enveloped virus by budding
Enveloped viruses release themselves from host cells through a process called budding, where the viral core, enriched with viral membrane proteins, buds out from the host cell membrane, acquiring a lipid envelope in the process.
-Bud becomes part of the envelope
-Ex. HIV
Bacteriophage
-Attachment: tail fibers attach to cell wall proteins
-Entry: viral DNA is injected into host cell
-Uncoating: not required
-Biosynthesis: in cytoplasm
-Chronic infection: lysogeny
-Release: Host cell is lysed
Animal viruses
-Attachment: attachment sites are plasma membrane proteins and glycoproteins
-Entry: Capsid enters by receptor-mediated endocytosis or fusion
-Uncoating: enzymatic rem of capsid proteins
-Biosynthesis: in nucleus (DNA viruses) or cytoplasm (RNA viruses
-Chronic infection: latency, slow viral infections; cancer (Ex. HPV linked to cervical or male genital cancer- due to latency)
-Release: enveloped viruses bud out; nonenveloped viruses rupture plasma membrane
Separating of viral nucleic acid from its protein coat is:
Uncoating- only occurs w/ animal virus replication
Papovaviridae
-2x stranded DNA, noneveloped viruses
-Causes warts- benign growth
-Anywhere on body
-HPC type 16 and 18 causes cancer
-Transmission: Direct contract; sexual contact; perinatal route
-Morphology: polyhedral- naked
-Latency- viruses integrate genome into host cell, dormant, then can be reactivated by stress or decrease in immune system
-Papillomavirus
-Signs and symptoms: pain, (plantars) warts
-Treatment: cryotherapy
-Genital warts
-Papillomavirus type 16 and 18
-Dx:
-physical exam- observe wart (benign wart)
-DNA probes/ molecular method
-Pap Smear
-Sample looked under microscope
-Ex. of infection- double-nucleated cells
-Treatment:
-Cryotherapy
-Podofilox (cream), Imiquimod
-Hysterectomy, Radiation (HPV 16, 18), chemotherapy
-Prevention
-Gardasil 9- HPV 6 and 11 (genital warts), HPV 16 and 18
Double stranded, enveloped viruses
SImplex virus (HHV- 1 (cold sores) and 2 (genital herpes)
Varicella(chicken pox)-zoster (Shingles) virus
Cytomegalovirus
Epstein-Barr virus
-herpesvividae
Herpesvivirdae
-DNA, enveloped
-Transmitted through infected secretion (ex. Through sexual contact)
-Hallmark characteristic of latency
-Recurrence or reactivation
-Dx: viral cell culture*- most accurate, takes weeks, antigen testing, nucleic acid amplification test (NAAT)- PCR
-cold sores, genital herpes, stromal keratitis, cancer, meningitis and encephalitis
Herpes simplex type 1: latency (cold sore)
-The initial infection occurs in 3-5 yrs children and symptoms include cold sores or fever blisters. The virus then moves up the trigeminal nerve where it remains latent in the sensor ganglia of the nerve
-Becomes latent in trigeminal nerve (along cheek)- symptoms go away
Latency
virus remains in host cell for a long period of time, away from immune system, no signs or symptoms for long period of time, not detected as foreign, then reactivated by stress or weakened immune system
Bacteria vs virus
Virus:
-Binary fission: no
-Intracellular parasite; yes
-Plasma membrane: no
-Passes through bacteriological filters: yes
-Posses both DNA and RNA: no
-ATP-generating metabolism: no
-Ribosomes: no
-Sensitive to antibiotics: no
-Sensitive to interferons: yes
-Treated w/ antivirals
Bacteria:
-Binary fission: yes
-Intracellular parasite: no
-Plasma membrane: yes
-Passes through bacteriological filters: no
-Posses both DNA and RNA: yes
-ATP-generating metabolism: yes
-Ribosomes: yes
-Sensitive to antibiotics: yes
-Sensitive to interferons: no
-Treated w/ antibiotics
Describe the chemical and physical structure of both an enveloped and a non-enveloped virus.
ENVELOPED: in some viruses, the capsid is covered by an envelope, which chemically, usually consists of some combination of lipids, proteins, and carbs. In most cases, the envelop contains proteins determined by the viral nucleic acid and materials derived from normal host cell componants. Structurally, the enveloped virus consists of the nucleic acid»Capsomeres» Envelop»Spikes(on some enveloped viruses).
NONENVELOPED are viruses whose capsids are not covered by an envelope. The capsid protect the viruses from nuclease enzymes in biological fluids and promotes the viruses attachment to susceptible host cells.
Viral species
A group of viruses sharing the same genetic info and ecological niche
Virion
A complete, fully developed viral particle
complete, infective form of a virus outside a host cell, with a core of RNA or DNA and a capsid.
Plaques
A clearing in a bacterial lawn resulting from lysis by phage
Describe how bacteriophages are cultured.
Bacteriophages can be grown either in suspensions of bacteria in liquid media or in bacterial cultures on solid media.
A viral plaque is a visible structure formed within a cell culture, such as bacterial cultures within some nutrient medium (e.g. agar). The bacteriophage viruses replicate and spread, thus generating regions of cell destructions known as plaques
Give an example of a family, genus and common name for a virus.
Common name: common cold virus
Genus: Rhinovirus
Family: Picornaviridae
Herpesviridae
-DNA, enveloped
-Transmitted through infected secretion (ex. Through sexual contact)
-Hallmark characteristic of latency
-Recurrence or reactivation
-Dx: viral cell culture*- most accurate, takes weeks, antigen testing, nucleic acid amplification test (NAAT)- PCR
Herpes simplex: type 1 (cold sore)
-The initial infection occurs in 3-5 yrs children and symptoms include cold sores or fever blisters. The virus then moves up the trigeminal nerve where it remains latent in the sensor ganglia of the nerve
-Becomes latent in trigeminal nerve (along cheek)- symptoms go away
-in herpesviridae family
Herpes Simplex: type 2
-Genital herpes
-Transmission: sexual and perinatal
-Men more symptoms than women
-Dx: PCR (NAAT)- if thought to spread to CNS, brain scan; DFA test- rapid antigen; viral culture
-Herpes Encephalitis (Rare)
-Latency in sacral nerves
-Acyclovir lessens symptoms
-Neonatal Herpes
-Acquired during passage of fetus through birth canal or transplacental (congenital)
-TORCH test panel for pregnant antibodies to HSV in mom’s serum; PCR test
-Chicken pox (Herpes Varicella)
-Signs and symptoms: fever, itchy vesicular rash
-Dx: rash- vesicles- viral cultures, antibody Titer, PCR test if believed to have spread to CNS, serological test for IgM (acute) and IgG (chronic infection)- indirect ELISA or IFA test
-Very contagious
-Transmission: droplets, close contact, perinatal
-Treatment: Acyclovir- not a cure
-Latency in nerve cells
-Prevention: vaccine
-Is the result of an initial infection w/ herpes varicella (DNA, enveloped)
-Causes pus-filled vesicles confined to face, through trunk
-Herpes zoster- shingles
-Signs and symptoms: burning, stinging, vesicular rash- one side of body
-Transmission: same as chickenpox
-Dx: same as chicken pox
-Treatment: Acyclovir- not a cure
-Prevention; Shingrix vaccine
-Reactivation of latent varicella-zoster virus due to stress, lower immunity
-Postherpetic neuralgia (chronic pain)
-Herpes Zoster Ophthalmicus
-Cytomegalovirus (HHV5)- cells swell
-Immunocompromised susceptible
-Latent in white blood cells
-Transmission: saliva and bodily fluids; congenital route- virus cross placenta and affect fetus
-Dx: viral cells culture- CPE- inclusions- granules containing viral infection, serology (quickest) for antigen-urine or antibody- blood serum, PCR
-Treatment: Acyclovir
-CMV diseases
-Congenital Cytomegaly- may result in still born- TORCH test on mother
-Retinitis- va impairment
-Immunocompromised- AIDS pt’s
-Pneumonia
- apart of herpesviridae
Infectious mononucleosis
-Epstein-Barr virus
-Transmission: saliva
-Signs and symptoms: swollen lymph nodes, fatigue, swollen spleen, sore throat, photophobia, malaise, fever
-Dx: monoslide test- heterophile antibodies: serology- screening test, specific antibody to Epstein-Barr virus required (IgM or IgG), DNA Assays available- reference lab
-self-limiting, supportive therapy- steroids- reduce inflammation
-Atypical lymphocytes- infects B-cells, becomes latent
-apart of Herpesviridae family
symptoms of hepatitis
Fever, hepatomegaly (enlarged liver), abdominal pain, rash, fever, joint pain/inflammation, low WBC count
Hepatitis B (HBV)
-in Hepadnaviridae family
-double stranded, Enveloped, DNA virus, spikes
-Transmission: blood/body fluids, sexual, perinatal, parenteral- puncture
-Carriers- secondary test- test (+) for surface antigen (HBsAg)
-Also make antibodies to the virus
-Dx: cannot be cultured, serological testing- detect HBsAg or antibodies to virus
-Dane particle (complete HBV)- virion- complete viral infection particle
-Envelope- where Hep B surface antigen is located (HBsAg)
-Incubation period: 26 days
-Chronic liver damage - could develop cirrhosis or liver cancer
-Could be latency- liver cells
-Could persist
-Treatment: antiviral agents: Alpha interferon
-Given in combo w/ other antivirals
-Severe: liver transplant
-Prevention: vaccine- actual virus is not used in this vaccine
-produced by S. cerevisiae that carries hepatitis-virus gene on plasmid
-has reverse transcriptase
-complication: cancer
Rhinovirus- common cold
-of Picornaviridae family- RNA
-single-stranded RNS, nonenveloped
-Transmission: direct contact/droplets; indirect contact- fomite
-Dx: signs and symptoms, viral culture
-Replicated in nasal cavity
-Signs and symptoms: runny nose and eyes, no fever, cough
-Treatment: otc med: aspirin; rest, fluids
-prevention: handwashing, social distancing
coronavirus
-Single-stranded RNA, enveloped
- of Coronaviridae family
-Colds
-SARS
-MERS-CoV
-Covid-19 (SARS-CoV-2)
-cytopathic effects: syncytia, cilia shrinkage, altered junctions between cells
-High mutation rate
-Signs and symptoms range from minor to life-threatening
-Transmission primarily droplets or aerosols
-Dx: rapid antigen or antibody tests; PCR test amplifies and detects viral RNA
-Treatment: Predesivir or Convalescent Plasma
-Prevention: vaccine- RNA based- can still get the disease, but symptoms less severe; masks
-Transmission: droplets
-RNA core
-Hollow cylinder capsid
-S-protein for attachment
Hepatitis C
-of Flaviviridae family
-single-stranded RNA, enveloped
-Incubation period- 22 days
-Transmission: same as HBV, more often through parenteral routes (IV drug use); rare- blood transfusion
-Chronic liver damage- cirrhosis (worse w/ Hep C)
-Necrosis
-Signs and symptoms: same as Hep B
-Dx: PCR for viral RNA (antibodies for HCV)
-Treatment: drug combinations (Peginterferon), liver transplant
-Prevention: no vaccine (due to rapid mutation), PPE
-Can be cured when viral RNA antibodies not found by medicine standards
-Viral persistence
Hepatitis D
-“Transmission”: Coninfected w/ Hep B
-single-stranded RNA, enveloped
-Similar to HBV in Transmission
-Prevention: Hep B vaccine- some protection
-family: Deltaviridae
-Enveloped, RNA virus
-genus: delta virus
Influenza A, B, C
-Orthomyxoviridae
-A: found in different animals, including ducks, chickens, pigs, whales, horses, and seals
-Transmission: droplets, close contact (direct), indirect contract- fomites
-Common Nov.-March
-HA spike (hemagglutinin spike for attachment to host)
-NA spike (neuraminidase (breaks down mucin (in mucous)) spike for viral assembly and release)
-Variation in H and N antigens
-Mutation of spikes- cannot get immunity from getting disease
-Orthomyxoviruses
-Influenza virus- RNA, enveloped
-The 3 types of influenza: A, B, and C
-Are distinguished by their matrix protein
-Orthomyxoirus Viral Genome
-An antigen drift occurs when the genome gradually changes to avoid host antibody
-An Antigenic shift occurs when influenza A acquires a new HA or NA gene; major genetic reassortment among different strains
-c: cause a mild respiratory illness and are not thought to cause epidemics
Influenza A and B viruses
-Lab dx: antigen detection- nasal washes/nasal swabs, viral culture, NAAT (PCR)
-Oseltamivir (neuraminidase inhibitors), Zanamivir (neuraminidase inhibitors- stop virus from getting assembled and released), newer antiviral agents
-Prevention: vaccine
-Signs and symptoms: fever and symptoms of common cold
-Envelope hemagglutinin spikes (H spike- cause RBCs to clump, and allows for attachment (HA spike))
-seasonal epidemics
Retroviridae
-Lentivirus includes
-Human Immunodeficiency Virus destroys helper CD4 T cells
-Use reverse transcriptase to produce DNA from viral genome
-HIV attachment and replication in T cell
-Transmission: blood and body fluids, sexual, perinatal (across placenta or through birth canal), blood transfusion (uncommon)
-Multiplication of a Retrovirus
1) Attachment via glycoprotein spikes
2) Then enters through diffusion
3) Uncoating
4) Reverse transcriptase- enzyme?
5) Latency as a provirus
-Latency: genome of virus in chromosome
6) Biosynthesis- replicate
7) budding
-Stages of HIV infection
-Phase 1: swollen lymph nodes (3 yrs into disease)
-Phase 2: fever, swollen lymph nodes, counts increasing in helper T cell?
-Phase 3: (8-10) CD4 count: low, susceptible to opportunistic infection: ex. TB, pneumonia
-Dx methods
-HIV antibodies by ELISA and Western blotting
-ELISA for detection of P24 (protein coat) antigen
-ctyopathic effects: destruction of T cells
Drugs that inhibit HIV life cycle
-Fusion inhibitors- block entry
-Reverse Transcriptase inhibitor- AZT
-Integrase inhibitor
-Protease inhibitor- block maturation
Highly active antirtroviral therapy (HAART)
-Combos of nucleoside reverse transcriptase inhibitors
-Non-nucleoside reverse transicpase inbitor of protease inhibitor
Treatments for viral infections and other antivirals
-Treatments of viral infections
-Nucleoside analogs
-Acyclovir: herpes virus
-(HAART) Zidovudine (AZT): HIV
-Other Antivirals
-Enzyme inhibitors- neuraminidase inhibitors: influenza, AIDS (RT inhibitors, protease inhibitors, integrase inhibitors, AIDS- fusion inhibitor)
-Alpha-interferon: viral hepatitis
Prions
-Prions-infectious proteins that are self-replicating
-Proteinaceous infectious particles
-Inherited and transmissible by ingestion (of meat- deer, food), corneal transplants, and surgical instruments for brain and eye surgery
-causes spongiform encephalopathies (brain becomes spongy-like, holes; no treatments, results in death (ex. Mad cow disease/bovine spongiform disease) in animals and humans
-eliminated by incineration
How a protein can be infectious
Changes shaped- pleaded- abnormal- scrapie protein PrPSc
Creutzfeldt-Jakob disease
-Signs and Symptoms: Memory loss, impaired sensed, rhythmic muscle contractions
-Prion-caused disease in humans
-eventually causes dementia and death
Describe how animal viruses are cultured
1) In living animals- animals are infected with virus and observed.
2) In embryonated eggs- Hole is drilled in the shell of the embryonated egg and a viral suspension is injected in the fluid of the egg. Viral growth is indicated by the death of the embryo or embryo cell damage.
3) In cell cultures- cells grown in culture media in the lab
List 3 techniques that are used to identify viruses
-Western blotting- virus’s reaction to antibodies
-PCR
-RFLP (restriction fragment length polymorphisms
Describe the lytic cycle of T-even bacteriophages.
1) Attachment: Phage attaches to host cell
2) Penetration: Phage penetrates host cell and injects its DNA
3) Biosynthesis: Phage DNA directs synthesis of viral components by the host cell
4) Maturation: Viral components are assembled into virions
5) Release: Host cell lyses and new visions are released
Describe the lysogenic cycle of bacteriophage lambda
Describe the lysogenic cycle of bacteriophage lambda
1) Phage attaches to host cell and injects DNA
2) Phage DNA circularizes and enters lysogenic cycle.
3) Phage DNA integrates within the bacterial chromosome by recombination, becoming a prophage.
4) Lysogenic bacterium reproduces normally.
5) Many cell divisions.
6) Occasionally, the prophage may excise from the bacterial chromosome by another recombination event, initiating a lytic cycle
Outline the steps in multiplication of both RNA and DNA animal viruses.
DNA:
1) Attachment- virion attaches to host cell.
2) Entry and Uncoating- virion enters cell, and its DNA is uncoated.
3) A portion of viral DNA is transcribed, producing mRNA that encodes early viral proteins.
4) Biosynthesis- Viral DNA is replicated, and some viral proteins are made.
5) Late translation: Capside proteins are synthesized.
6) Maturation- virions mature.
7) Release- virions are released.
RNA:
1) Attachment
2) Entry and uncoating- ssRNA: + or sense strand, ssRNA: - or antisense strand, dsRNA: + or sense strand with - or antisense strand
3) RNA replication by viral RNA-dependent RNA polymerase.
4) Translation and synthesis of viral proteins
5) Maturation and release.
Rubella
-pathogen: rubivirus
-family: matonaviridae
-transmission: respiratory route, aerosol
-signs and symptoms: red rash (less extensive than measles, and shorter recovery time) light fever,
-prevention: vaccine
-treatment: none
-complications: rare but can cause encephalitis in adults
Respiratory Syncytial virus (RSV)
-pathogen: Orthopneumovirus
-Pneumoviridae family
-single-stranded RNA, enveloped
-causes cell fusion when grown in cell culture
-signs and symptoms: mild cold-like symptoms, but can cause life-threatening pneumonia in very young infants or older adults, coughing, wheezing, fever only in cases of bacterial complications
-sometimes implicated in cases of otitis media
-dx: serological tests and rt-PCR- samples of respiratory secretions to detect both antibodies and the virus
-treatment: Riboviran and Palivizumab
-transmission: direct contact and droplets
-prevention: vaccine for older adults and and very young infants, handwashing
Mumps
-prevention: vaccine- 15mo old
-pathogen: orthorubulavirus
-family: paramyxoviridae
-single-stranded RNA, enveloped
-targets parotid glands
-signs and symptoms: painful swelling of one of both parotid glands, fever, pain when swallowing
-transmission: saliva, respiratory secretions
-viremia (presence of virus in the blood) begins several days before onset of mumps symptoms and before the virus appears in saliva -complications: hearing loss, meningitis, inflammation of ovaries or testes, pancreatitis
-treatment: rest, advil or Tylenol for pain
Measles
-pathogen: morbilivirus
-family: Paramyxoviridae
-single-stranded RNA, enveloped
-cytopathic effects: cell fusion
-complications: rare form of encephalitis- acute sclerosing panencephalitis (SSPE), middle ear infections, pneumonia, and secondary bacterial infections.
-once acquired, immunity is lifelong
-prevention: vaccine
-transmission: respiratory route
-signs and symptoms: macular lesions appear on the skin, and Koplik’s spots appear on the oral mucosa.
-treatment: otc fever reducers
Smallpox
-pathogen: orthopoxvirus
-family: poxviridae
-double-stranded DNA, enveloped
-first disease to be artificially induced and first to be eradicated from human pop
-transmission: aerosol
-signs and symptoms: pustules that may be nearly confluent on skin
-treatment: none
Varicella-zoster
-Pathogen: varicellovirus
-prevention: vaccine
-transmission: aerosol
-treatment: acyclovir
-signs and symptoms: fever, blisters, red spots, fatigue, itching
Hepatitis A
-single-stranded RNA, noneveloped
-prevention: vaccine
