lesson five Flashcards
viruses
- infectious particles
-must be treated using different therapeutic strategies than
other microorganisms because they are different in
makeup and structure
transmission of viruses
blood transfusion, mucus droplets, aerosols, fomites,
air (airborne), water, food, vectors
Virus Size
- smaller than most bacteria
- always obligate intracellular parasites
virion
complete infectious viral particle with nucleic acid surrounded by protein coat
viral structure
- RNA or DNA and capsid (protein coat) comprised of capsomeres (protein molecules)
- complete unit: nucleocapsid
- some viruses have “lipid envelopes” outside of the
nucleocapsid - glycoproteins or spikes inserted in enveloped or capsid
virus host range
- different viruses can infect every life form
- usually fairly specific host range or specificity
bacteriophages
- viruses that infect bacterial cells and can transfer new genes from one bacteria to another
- can transfer genes for production of toxin
classifying viruses
- viruses are grouped into families on basis of DNA or RNA genome composition
- RNA viruses are known for their ability to mutate quickly
DNA viruses
- Papillomaviridae (HPV)
- Adenoviridae (adenovirus)
- Hapadnaviridae (hepatits B virus)
- Herpesviridae (HSV-1, HSV-2, HHV-3…)
- Poxviridae (smallpox, monkeypox)
- Parvoviridae (B-19)
Viral infection: attachment and penetration into host cell
a) virus must attach to host cell, usually to receptors
b) two processes for penetration of the virus into the host cell: Fusion and Pinocytosis
viral infection: replication of the genome
- DNA forms the genome of all organisms
- Transcription of the DNA gives rise to a RNA molecule that is almost an
exact copy of the DNA - protein is synthesized
what is the goal of a virus
to replicate itself
can viruses have two types of nucleic acid
- viruses have only ONE type of nucleic acid (DNA or RNA)
DNA viruses replication
Host cell DNA polymerase may be used directly
to make more virus DNA (if replic. in host cell nucleus)
viral DNA → viral DNA
RNA viruses replication
Virus must carry its own RNA polymerase
enzyme to produce RNA from viral RNA (no RNA
polymerase in host cells)
viral RNA → viral RNA
retrovirus replication
carries its own reverse
transcriptase enzyme in the virus capsid:
viral RNA → viral DNA integrated into the
chromosome → viral RNA
assembly of new virus
- Association of newly replicated RNA or DNA (nucleic acid) with newly made
viral proteins results in new nucleocapsids
release of new enveloped virus
envelope components are produced and inserted into the host cell plasma membrane, the viral particle then attaches to the plasma membrane and buds through
fuzeon (antiviral drug)
stops entry (fusion) of HIV into cells
acyclovir (antiviral drug)
stops replication of herpes viruses by interfering
with the viral DNA polymerase
tamiflu (antiviral drug)
stops budding/release of influenza
virus from host cell
acute or productive infection
- virus replicates, produces many virions
- host cell often killed= lytic infection
latent infection
viral genome persists in host cell but does not replicate- provirus
chronic infection
virus replicates without causing host cell lysis and can persist for long periods of time
what virus causes acute chickenpox infection
Caused by an enveloped DNA virus, HHV-3, sometimes called “varicella”
chickenpox acute infection symptoms
- fever, itchy rash
- rash is spread on trunk and head
- virus particles in rash can escape and infect
- skin vesicles always present in different stages of lesion formation
- When lesions heal, the virus travels up the nerve that
ennervates the skin at the site of the lesion and makes a home in the peripheral nerve ganglion where it remains latent
chickenpox latent infection
- virus is present but no replicating until triggered by external factors, then travels down nerve to skin and reactivates
what is reactivation known as in HHV-3
shingles or zoster
shingles or zoster
- reactivation of the virus as it travels back down the nerve to skin from the site of latency
- begins as a local skin rash
- characterized by confluent rash and pain
- untreated rash lasts 2-5 weeks, infectious to those who have not had chicken pox
chicken pox complications
- most common in immunocompromised is secondary bacterial infection
- CNS disease: encephalitis, meningitis, myelitis
zoster complications
- PHN (Post Herpetic Neuralgia) most common complication
- 25-50% of patients >50 yrs develop PHN
- Pain that persists for months or years
- Can cause permanent nerve damage so important to get
treatment (acyclovir) within 48-72 hours of symptoms
appearing
prevention of chickenpox
active immunization:
- live attenuated vaccine
passive immunization:
- effective up to 3 days post-exposure
- VZIG antibodies to the virus
- normally for immunocompromised exposed children and neonates born to mothers with varicella
chickenpox
lesions are in different stages of development
smallpox
all lesions are in the same stage of development
oncogenic viruses
- Some viruses can “transform” normal host cells to cancer cells
- Not all “transformed” cells become cancerous e.g. wart virus:
often benign tumours- Cancer-producing viruses can be RNA or DNA viruses
PCR viral diagnosis
polymerase chain reaction
- molecular biology technique used to detect the genes in an organism
prions
- protein misfolding disease
- self protein becomes changes and nonfunctional
- prions are misfolded proteins that act as infectious agents in susceptible exposed animals
human prion disease
always fatal
human prion disease signs
- ataxia
- Cortical visual symptoms
- Progressive dementia
- Myoclonus
- Akinetic mutism
average death time after onset :4 months
