viruses Flashcards
what is viral pathogenesis
processes by which viral infection results in a disease.
7 stages of viral replication
Adsorption,
Entry,
Uncoating,
Transcription/mRNAproduction,
Synthesis ofviruscomponents,
Virionassembly
Release (Liberation Stage).
what is adsorption in viral replication
The virus becomes attached to the cell by specific cellular receptors which can be glycoproteins, phospholipids or glycolipids.
what is entry in viral replication?
Following adsorption, the virus can enter the cell, most commonly via receptor-mediated endocytosis. This is the same process by which many hormones enter the cell.
what is uncoating in viral replication
Once inside the host cell, the viral capsid must be uncoated to release the viral nucleic acid. Uncoating may be achieved by host or viral enzymes that will degrade the capsid.
what is Transcription/mRNAproduction, synthesis ofviruscomponents
Once uncoated, viruses (DNA or RNA) replicate by switching the host machinery from cellular protein synthesis to viral synthesis and viral proteins are produced.
what is Virionassembly in viral replication
Newly synthesised viral proteins are post-transcriptionally modified and packaged into virions that can be released from the infected host cell to infect other cells.
what is Release (Liberation Stage) in viral replication
Virions are released from the cell either by lysis or budding. In lysis, the infected cell dies and the virions are released. In budding, the virion takes some of the host cell’s membrane with it as it leaves – this normally does not kill the infected cell.
what is Horizontal transmission
between members of same species
what is Zoonotic transmission
between members of different species
what is Latrogenic
activity of health care worker leads to infection of patient
what is Nosocomial
when an individual is infected while in hospital or health care facility
what is Vertical transmission
transfer of infection between parent and offspring
what is Germ line transmission
agent is transmitted as part of the genome
how do you acquire an infection from the respiratory tract
Most common route of viral entry
Viruses enter by aerosolized droplets from cough or sneeze, or contact with saliva
Large droplets lodge in nose; smaller in airways or alveoli
how do you acquire an infection from the alimentary tract
Eating, drinking, social activities introduce viruses into the alimentary tract.
good opportunities for virus-cell interactions.
Extremely hostile environment.
Viruses that have evolved to infect are resistant to these factors.
how do you acquire an infection from the urogenital tract
Protected by mucus, low pH
Minute abrasions from sexual activity may allow viruses to enter
Some viruses produce local lesions (e.g. HPV)
Some viruses spread from urogenital tract (e.g. HIV)
how do you acquire an infection from the eye
Sclera and conjunctiva entry route.
Infection usually occurs after injury and/or ophthalmologic procedures.
Disseminated infection: e.g. enterovirus 70 spread to CNS
HSV-1 can infect cornea, blindness may result, virus spread to sensory ganglia
how do you acquire an infection from the skin
Outer layer of dead cells cannot support infection
Epidermis is devoid of blood or lymphatics - so local replication only.
Dermis and sub-dermal tissues are highly vascularized - infection may spread.
what is disseminated spread
when viruses spread beyond the primary sire
what is systemic spread
when viruses infect many organs
what is hematogenous spread?
Viruses that produce disseminated infection often do so by entering the blood
Virus in extracellular fluids are taken up by lymphatic capillaries
Once in blood, virus has access to almost every tissue
Other viruses spread freely in the blood
(viremia)
what is viremia
Presence of infectious virus in the blood
what is active viremia
results from virus replication
what is passive viremia
results from virus introduced into the blood without replication
what is neural spread of viruses
viral entry to local nerve endings
what is a neuroinvasive virus
a virus that can enter the CNS after infection of a peripheral site
what is a neurovirulent virus
a virus that can cause disease of nervous tissue
what is tissue tropism
the spectrum of tissues infected by a virus
what are pantopic viruses
a virus that can replicate in many organs
what is determines a virus
Cell receptors for viruses
Cellular proteins that regulate viral transcription
Cellular proteases involved in the maturation of virions
what is viral virulence
The capacity of a virus to cause disease in an infected host
what is the difference between a virulent, avirulent and attenuated virus
A virulent virus causes significant disease, while an avirulent or attenuated virus causes reduced or no disease
how is virulence quantified
LD50 (Lethal Dose 50%; the amount of virus needed to kill 50% of infected hosts)
the meantime to death
the meantime of symptoms
measurement of fever, or weight loss
measurement of pathological lesions (poliovirus); reduction in blood CD4+ lymphocytes (HIV-1)
what are the Viral genes affecting virulence classes
Those that affect the ability of the virus to replicate
Those that modify the host’s defense mechanisms
Those that enable the virus to spread in the host
Those which have intrinsic cell killing effects
what are features of virokines and viroreceptors
Mimic normal cellular molecules critical to host defense
sabotage the body’s innate and adaptive defenses
not required for growth in cell culture
how do you detect an antibodu in the plasma
via serolology
explain the steps of ELISA
it is an enzyme-linked immunosorbent assay
substrate changes colour when enzyme is removed
how do you detect a viral antigen
immunoflouresence
need manufacturing of specific monoclonal antibodies
how do you collect specimens from respiratory tract
Nasal and bronchial washings, throat and nasal swabs, sputum
how do you collect specimens from the eye
throat and eye swab/scraping
how do you collect specimens from the gastrointestinal tract
stool and rectal swabs
how do you collect specimens from the vesicular rash
vesicle fluid and skin scrapings
how do you collect specimens from maculpapular
throat, stool and rectal swabs
how do you collect specimens from the CNS
stool,tissue, saliva, brain biopsy and cerebrospinal fluid
how do you collect specimens from the gentials
vesicle fluid or swab
how do you collect specimens from urinary tract
urine
how do you collect specimens from blood borne
blood
what are measures to prevent viral infection
General measures e.g. gloves, masks, etc
Specific measures (long-term or short-term prevention) e.g. vaccines, chemoprophylaxis, immunoprophylaxis
how long does it take to get any information from an infection
24 hours
how long does it take to get definitive information about an infection
48 hours
what information is required to treat an infection
A knowledge of what bacteria cause what syndromes of infection (UTI, pneumonia etc)
A knowledge of resistance rates
Diagnostic microbiology
Corrects your initial diagnosis
Allows you to focus your treatment
Informs the epidemiology
what are the situations where you use a special stain
Other organisms eg TB
Electron microscopy for viruses
Direct visualisation of parasites and eggs
what is an API test
API (analytical profile index) strips give accurate identifications based on extensive databases and are standardized, easy-to-use test systems.
what are the advantages and disadvantages of API’s
Good for detecting bacteria you can stain and grow
Reliable identification and resistance testing
Can be slow and labour intensive
what is PCR
PCR is a technique that takes a specific sequence of DNA of small amount and amplifies it to be used for further testing.
what is the purpose of PCR
To amplify double-stranded DNA molecules with the same (identical) size and sequence by enzymatic method and cycling condition.
what are the steps of PCR
- Denaturation of ds DNA template
- Annealing of primers
- Extension of ds DNA molecules
Explain denaturation in PCR
Temperature: 92 – 95°C
Double-stranded DNA melts -> single stranded DNA
explain annealing in PCR
Temperature: 50 – 70°C (depending on the melting temperature of the expected duplex)
Primers bind to their complementary sequences
explain extension in PCR
Temperature: 72°C
Time: 0.5 – 3mins
DNA polymerase binds to the annealed primers and extends the DNA from the 3’ end of the chain
why do you do whole genome sequencing
Sequencing entire DNA of bacteria and viruses
Compare strains to see how related they are/evolve
Interrogate for antibiotic resistance genes
what are the advantages of whole genome sequencing
Set to revolutionise diagnosis of infection
Rapid (hours)
Cheap (comparable to culture)
Desktop Platforms
what are you usually investigating using tissue cultures
Cytopathic effects on cells
Expression of viral proteins detected at the cell surface
what is infection classified by
are classified by the causative agent as well as by the symptoms that are produced.
what is an apparent infection
one that produces symptoms
what can an infection that is active, but does not produce noticeable symptoms called
apparent, silent or subclinical
what is a latent infection
an infection that is inactive or dormant
what is the pathway of infection
mode of transmission
portal of entry
susceptible host
causative agent
reservoir
portal of exit
how to break the chain of infection from a causative agent
Rapid and accurate identification of organism:
Routinely screen samples and equipment.
Control or eliminate infectious agents:
Proper cleaning with water/mechanical action with detergents
Disinfection
Sterilization
what is a reservoir
A reservoir is the place where the agent survives, grows, and/or multiplies: human, animal or environment.
how do you break the chain of infection from the reservoir
Occupational health:
Immunization and regular check ups.
Environmental disease:
Cleaning hospital with disinfectant
Clean bed/furniture between patients
how do you break the chain of infection from the portal of exit
Practice aseptic precaution
Wearing masks
Careful handling of waste
Wear disposable gloves
how do you break chain of infection from mode of transmission
Contact Precautions:
Single patient room
Good hand hygiene, PPE as appropriate.
Remove PPE when leaving.
Clean and disinfect non-disposable equipment and items
Droplet Precautions:
Single patient room
Surgical masks
Limit patient movement outside the room
Airborne Precautions:
Negative pressure
N95/P2 masks
Limit patient movement outside the room
how do you break chain of infection from portal of entry
Maintain integrity of skin and mucous membranes
Turning and positioning of debilitated patients
Ensure personal hygiene of patients
Disposal of contaminated sharps
Handling of catheters and drainage
how do you break chain of infection from susceptible host
Protecting the susceptible host:
Oral hygiene
Maintaining adequate intake
Encouraging exercise
Encouraging immunization
Maintaining healing process:
Balanced diet
Appetite of patient
Reduce stress
what is an acute infection
sudden and rapid onset of a disease
what is a chronic infection
continued infection by the primary agent for a long period- often following primary infection
what is primary infection
the initial infection of a host by a pathogen
what is a latent infection
a persistent infection that does not have any symptoms after the primary infection
what are features of latent infections
DNA viruses or retroviruses
Persistence of viral DNA
Retrovirus infection may induce cellular transformation
what are professional pathogens
almost always cause disease
what are opportunitic pathogens
only cause disease in immunocompromised patients
what is pathogenicity
the capacity of an organism to cause disease
what is virulence
the degree of pathogenicity caused by an organism
what is commensal
an organism that recieves benefit from the host without causing harm
what does pathogenicity depend on
The organism’s virulence but also…
Where it is
Immune state of the patient
