Norma Flashcards
What is a virus?
- small (go through a filter)
- small genome packaged as a nucleoprotein
- a capsid holds in the nucleoprotein
- may have an outer plasma membrane (envelope)
- obligate parasites
- classified by the disease they cause or the organ system they infect
List the symptoms that can lead to a differential containing a viral infection?
- rash
- fever (most viruses)
- conjunctivitis
- pharyngitis (especially respiratory viruses)
- hepatitis
- pneumonia
- bronchiolitis
- adenopathy
- parotitis
- meningoenecephalitis
- arthritis
- congenital or perinatal disorders
What are the categories and types used in the Baltimore classification for viral identification?
- DNA viruses - Double stranded (ds) DNA, Single stranded (ss) DNA
- RNA viruses - dsRNA, ssRNA(+), ssRNA(-)
- Retro-transcribing viruses - ssRNA (RT), dsDNA (RT)
What is a serotype?
- A subset of a species
- when immunity developed it will only be to that specific serotype
What is the classification of diagnosis used for?
- to determine how to treat the disease
- to determine the best method of disinfection or prevention of infection
What determines virus classification?
- disease produced
- physical characteristics (structure, envelope)
- Genome sequence is primary characteristic
What is the importance of the outer envelope?
- developed during budding of the virion
- contains glycoproteins that interact with the receptors on the eukaryotic cells
What are the differences between RNA and DNA viruses in their speed of replication?
- RNA viruses evolve rapidly but at a high error rate due to RNA-dependent-RNA-polymerase
- DNA viruses evolve more slowly due to the need to be in the nucleus and use the host cells transcription enzymes but at a low error rate
What is often packaged within a virus particle?
- nucleoprtein - protein and genome complex
- polymerase (RNA/DNA dependent)
- protease for further capsid breakdown and to cleave polycystronic mRNA
What are the typical shapes for capsids?
- icosahedral and helical
- complex viruses
What is the epidemiology of viral infections
- present on fomites
- present on droplets - may be inhaled or contact fomites
- present in body fluids
- transmitted by vectors
What are some modes of transmission for viruses?
- respiratory
- fecal-oral
- sexual transmission
- direct contact
- urine-associated transmission
- parenteral transmission
- vertical - mother to child
- arthropod-borne transmission
- zoonotic infections
What is tropism?
- classifying a virus by the organ system that it infects and replicates in
What are the targets of antiviral therapy?
- polymerases
- viral proteases
- viral capsids
- immune activators (interferon beta)
- immunoglobulin treatment (antiviral antibodies)
How does ssRNA (+) viruses replicate?
- virus binds and enter cell and releases RNA
- RNA is then translated (cells normal translation is stoped)
- virion RNA then copied by RNA dependent RNA polymerase
- both occur in the cytoplasm and then cause lysis of the cell
How does a DNA virus replicate?
- virus binds and enters cell and releases viral DNA into the nucleus
- transcription of the viral DNA by host’s enzymes
- production of DNA rpeplication proteins and capsid proteins
- viral DNA and viral proteins are packaged within a capsid and then bud off from the cell membrane
How does a retrovirus replicate?
- virus binds and enters cell
- reverse transcriptase make a cDNA copy of viral genome and releases cDNA into nucleus
- viral DNA is then integrated into the host genome and replication of the cDNA and viral protein production occur
- viral RNA and proteins are encapsulated and then bud off from the plasma membrane of the cell
What is the difference between primary infection site, secondary infection site and viremia?
- Primary - site of first replication of virus
- Secondary - pathogenic virus replication in secondary organs after viremia
- Viremia - virus circulating in the blood stream
What is the difference between acute an chronic viral infection?
- Acute - can be cleared by the body
- Chronic - isn’t cleared and virus remains within cell - dormant or persistent
What is meant by persistent viral infections?
- infections that are not cleared after the acute period of infections and leads to chronic infection
What is meant by a latent viral infections?
- infections that enter a dormant phase where the virus does not replicate but remains uncleared from the body
- will have episodes of reactivation in which the virus replicates and causes symptoms
What are perinatal viral diseases?
- infection before birth from the mother, at birth or from breast milk after birth
What are some perinatal diseases caused by viral infections?
- HIV - leads to AIDS
- Parvovirus - miscarriage, hydrops fetalis
- Rubella - hearing loss and other teratogenic effects
- CMV - hearing loss and neurologic complications
- Herpes simplex
- HBV - leads to chronic infection but premature manifestations
- Hep E - increased mortality of pregnant women
- Enterovirus - multi-organ disease of neonates
What are some connections between cancer and viruses?
- Hep B,C - hepatocellular carcinoma, cholangiocarcinoma
- HPV - cervical cancer and oropharyngeal cancer
- Epstein-Barr virus - lymphoma
- HHV8 - Karposi’s sarcoma, lymphoma
- HTLV1 - T-cell lymphoma
What are causes of epidemics of viral infections?
- re-emerging viral infections
- viruses new to human beings
- new medical, cultural and agricultural practices results in new transmission
What is the difference between indirect and direct testing?
- indirect testing is a test for immune consequences of viral infections
- direct testing is for the virus, viral protein or nucleic acid
What are three presumptions of signs/symptoms and diagnostics of virology?
- some presentations are definitive without testing
- during outbreaks, pts with the same symptoms will have the same infections
- some tests are too expensive or take to long
What are some direct methods of viral infection detection?
- culture live virus
- electron microscopy for viral structures
- antigen (protein fragments)
- DNA/RNA genome
What are some characteristics of culturing live virus?
- expensive and time consuming
- not always possible
- usually type of virus is needed to be known
- morphology can be examined
- determine cytopathic effect
What is the cytopathic effect?
- when virus is within the cell the cell will die
What are some characteristics of electron microscopy?
- allows identification of the viral family but not serotype
What is hemagglutination?
- a quantification test
- adding virus and RBC and see if agglutination occurs and if so then the virus has that capability
What are some characteristics of antigen detection?
- uses a virus specific antibody
- antibody on a well will bind to the viral antigen and then a second AB (with attached indicator) will bind to the antigen
- amount of indicator within wells will show amount of viral antigen
What are some characteristics of Direct Fluorescence Assay?
- an antibody that has fluorescence attached is added to a specimen and when bound to the viral antigen the fluorescence will be visible
What is the advantage of PCR and RT-PCR?
- the procedure is extremely sensitive and specific
What are some indirect methods of viral infection detection?
- ELISA
- Indirect immunofluorescence assay
- detection of specific AB types (titer draws)
- Western blot
What are some examples of upper respiratory infection?
- rhinitis
- pharyngitis
- sinusitis
- laryngitis
What are some examples of lower respiratory infections?
- bronchitis
- bronchiolitis
- pneumonia
What are some viral infections resulting in the common cold?
- rhinovirus
- coronaviruses
- Respiratory syncytial virus (winter)
- Adenovirus (summer)
- Parainfluenza virus (winter)
Discuss some childhood respiratory infections and their characteristics.
- rhinovirus - associated with asthmatic episodes
- parainfluenza virus - many types, seasonal
- Respiratory syncytial virus - pneumonia
- Metapneumovirus - LRI
- Human herpes virus 6 - interstitial pneumonia
- Enterovirus infections - summer cold
What are the types of Parainfluenza virus?
- HPIV-1,2 - childhood croup (fall)
- HPIV-3 - spring and early summer
- HPIV-4 - less common
What are some common routes of transmission of respiratory viruses?
- contact with secretions
- contact with aerosolized microdroplets
- hands to the eyes
- inhalation
- fomites
What are three respiratory virus families?
- Orthomyxoviruses - influenza
- Paramyxoviruses - parainfluenza (mumps), morbillivirus (measles), respiratory syncytial virus, metapneumovirus
- Adenoviruses
What are the characteristics of RSV?
- most common respiratory virus in infants
- extreme pathogenic effect on reparatory epithelium
- recovery is longer than bacterial infections
What are the characteristics of Adenoviruses?
- many serotypes
- can cause myocarditis in children
- cause conjunctivitis
What are some characteristics of Orthomyxoviruses?
- contain hemagglutinin proteins and neuraminidase proteins
- contains 3 types A, B, C
- negative strand genomic RNA
Describe the subtypes of influenza viruses.
- A - pandemic and seasonal - between humans and animals - LRI
- B - seasonal - humans only - LRI
- C - mild illness - URI
What are the actions of the orthomyxovirus proteins?
- Hemagglutinin - allows attachment
- Neuraminidase - allows release of newly made virus particles from cells
What is the idea of antigenic drift?
- mutations that occur during replication will lead to a drifting into new antigenic shapes
- virus can escape the immune system
What is the idea of antigenic shift?
- genetic changes occur that allow a virus to jump from species to species
- can occur with or without genetic mixing and may include an intermediate host
What are pandemics?
- caused when a virus enters the human population and spreads world wide
What causes a pandemic?
- a novel virus with little/no immunity
- capability to replicate in humans
- pathogenic and virulent in humans
- capable of human to human transmission
What is the difference between the vaccines and antivirals?
- vaccines are the best prevention option but efficacy is dependent ton a correct match
- antivirals are meant to stop the spread
