Part I: General Characteristics of Viruses
inactivated virus
"killed" virus -whole virus is killed and the administered as an antigen *result*: stimulates the host immune system -often requires a series of shots to adequately stimulate the immunity
attenuated virus
"live" virus -attenuated means reduced virulence -vaccines produces a very limited infection in the host *result*:stimulates the host immune system -immunity is usually long lasting
virus components
*capsid*: outer protein coat, composed of protein subunits called capsomeres *nucleic acid*: DNA or RNA = *nucleocapsid*
enveloped with spikes *influenza*
*hemagglutinin*: binds to host cell receptor (on RBCs and other host cells) *neuraminidase*:viral enzyme that assists penetration through the mucous protection the respiratory epithelium
antigenic shift
*major* change in surface proteins *caused by*: recombination of genes from different virus types *results in*: major influenza pandemic
antigenic drift
*minor* change in surface proteins *caused by*: recombination of genes from different virus types *results in*: influenza epidemic
chicken pox and shingles
*varicelle-zoster virus*: (VZV) a herpes virus, causes chicken pox and shingles *reservoir* infected humans
interferon
-host defense against viruses; it puts the host cells in an antiviral state -stimulates production of antiviral proteins in host cells, to prevent their infection by the virus
viruses
-non living -very small and simple structure -acellular, infectious particles -obligate intracellular pathogen (only replicate within living host cells)
goal of immunization:
-stimulate the production of neutralizing antibodies in the host -confer long term protective immunity in the host
serological tests
-test for specific antibodies to a particular virus in the patients serum -presence of antibodies indicates an immune system reaction produced by the host in response to the virus
latent infection
-viral genome is stably integrated into host cell chromosome -no active viral replication -DNA and RNA viruses are able to produce latent infections
varcella (chicken pox)
an acute, generalized viral infection, with fever and skin rash. vesicles also form in mucous membranes. usually mild, self limiting disease but can be damaging to a fetus -leading cause of vaccine preventable death in US -*transmission*: respiratory droplets & skin contact -*incubation period*: roughly 2 weeks -begins in respiratory tract, localizes to skin -resolves in 5-10 days -*complications*: pneumonia, secondary bacterial infections
virion
complete, mature, infectious virus
rapid tests (antigen detection)
detect visions or virus parts in a specimen from a patient ex: rapid test to diagnose influenza
what units are used to measure viruses?
nanometers most viruses are 10-300nm in diameter
do antibacterial drugs work against viruses?
no, bacterial targets aren't present. bacteria are prokaryotes, viruses use eukaryotic cell processes for replication
are we able to view viruses with a light microscope?
no, we need an electron microscope
burst size
number of new phages released typical burst size is 50-200 phages
subunit vaccines
one component of the virus, usually a protein, stimulates a host immune response -no intact virus is involved
family names end in...
viridae ex. herpesviridae
genus names end in...
virus ex: simplexvirus
bacteriophage
virus that infects bacteria
animal viruses
viruses that infect humans and animals
cytopathic effect
visible effect of the viral infection on the cultured cells -cell swelling -cell fusion -cell death
can genital herpes be caused by cold sores?
yes
how do viruses cause disease?
-viruses only infect cells bearing appropriate surface receptor. viruses are specific as to the types of cells that the can infect -viruses multiply within host cells and it is during their escape from those cells by either lysis or budding that the host cells are destroyed. -cell destruction leads to most of the symptoms of the viral infection which vary depending on the location of the infection
viruses have specific receptors for interacting with host cells, their infectiousness is limited to a particular host or cell type
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what is the connection between chicken pox and shingles?
...
bacteriophage replication
1. *attachment*: phage binds to receptor of the surface of the bacterial cell wall 2. *penetration*: phage injects genetic material into the bacterial cell 3. *biosynthesis*: synthesis of viral nucleic acid, proteins and other components within the host cell 4. *maturation*:assembly of newly synthesized components into complete virions 5. *release*: host cell bursts and new virions escape from the bacterial cell
replication of animal viruses
1. *attachment*: viral capsid, spike or envelope interacts with receptors on plasma membrane 2. *penetration*: for animal viruses, usually entry of shoe virus into cells. occurs in 2 ways. 3. *uncoating*: viral nucleic acid escapes from the capsid 4. *maturation of viral nuleocapsids*: viral nucleic acid is packaged into viral capsids and usually occur via self assembly 5. *release of mature virions*: unenveloped viruses generally lyse the host cell and enveloped viruses must get their membrane and leave via budding
two types of herpes simplex virus
1. HSV type 1 *typically* causes cold sores 2. HSV type 2 *typically* causes genital herpes
viruses have a genome that consists of the following:
1. double stranded DNA 2. single stranded DNA 3. double stranded RNA 4. single stranded RNA
basic shapes of viruses
1. helical 2. polyhedral 3. complex
advantage to provirus
1. host immune response can't reach virus 2. provirus is propagated each time host cell divides 3. virus can re-initiate infection later
three control strategies for any infectious disease
1. treat infection 2. precent disease within the host 3. interrupt transmission of the virus
influenza
RNA virus with 10 genes *transmission*: airborne spread and direct contact with respiratory secretions *incubation period*: 36-48 hours *treatment*: antiviral drugs *immunization strategy*: flu shot
are we able to culture viruses on TSA? blood agar? why or why not?
TSA - no Blood agar - no we can't lay viruses where there is no "live" cells
provirus
a virus that has stably integrated viral DNA into the host cell's chromosome, resulting in latent infection
influenza B
active every year, less widespread usually confined to schools and workplaces
symptoms of influenza
acute, viral respirator infection with fever, chills, headaches, aches, sore throat, cough, nasal drainage, nausea, vomiting, and diarrhea
what are some difficulties regarding antiviral agents?
anti viral agents have sever side effects: -its difficult to kill the virus without killing the host cell -hard to inhibit an "inert particle"
key concept:
antivral treatments are few and less effective -antiviral drugs inhibit replication but do *not* kill the virus
how does the herpesvirus "hideout" in nerve ganglia?
as a provirus
human papillomaviruses (HPV)
can produce warts or cervical cancers *reservoirs*: infected humans *disease*: epithelial cells become infected and begin to divide warts usually last for years, (spontaneously regress) virus remains in surrounding tissue and wart may reoccur *transmission*: dermal warts (direct contact or for mites) and genital warts (sexually transmitted) warts are easily transmitted from one area of body to another *treatment*: cryotherapy or caustic chemicals *vacines* HPV vaccine
influenza A
causes severe symptoms and is associated with epidemics and pandemics
what does the influenza virus usually infect?
epithelial cells in upper respiratory tract including ciliated epithelial cells. -concern is secondary bacterial infections or viral pneumonia -*reason*: respiratory epithelial cells are damaged and destroyed including the protective mechanisms of cilia
influenza virus is known for its antigenic variation... why?
for its ability to change its surface proteins so host is unable to develop an effective immune response
why are HSV infections latent?
infected person is always harboring the virus in nerve cells -tropism for nerve tissue -travels down the nerve tissue and resides in nerve ganglia -reactivation by trauma, fever, stress, uV light, menstruation, injury
influenza types?
influenza A influenza B influenza C
herpes zoster (shingles)
its a recurrent infection of VZV, often a result of immunosuppression. -*triggered* by: stress, radiation therapy, immunosuppression and aging -you get shingles from your on chickenpox virus -can't "catch" shingles -people are only contagious to persons who have *not* had chickenpox -*treatment* antivirals
herpes simplex virus
large, enveloped *reservoir*: infected humans initial infection may be asymptomatic
influenza C
rare, may cause less significant disease
tissue tropism:
refers to the cell types a virus can infect -host cell must have receptor for the virus -most viruses are limited to only specific cells and or tissues of the host
host range:
refers to the spectrum of host that a virus can infect -determined by what the virus can bind to -host range can be narrow or broad -most viruses are limited to only one host
what happens if you stop taking the antivirals?
replication resumes
enveloped viruses
some viruses possess an additional lipid and protein covering that lies external to the capsid called an envelope.
lysogeny
temperate phages undergo adsorption and penetration into the bacterial host but aren't replicated or released immediately. the host chromosome carries bacteriophage DNA is called lysogeny
burst time
time from phage attachment to lysis may take 20-40 minutes
interferons are non-specific host defenses? true or false?
true. they aren't targeted to a specific virus, active against many viruses
presentation and symptoms
unique presentation and symptoms of a viral infection point to a specific and causative virus
