Viruses Flashcards
viruses are obligate intracellular parasites because
- they cannot reproduce without a host
- not considered to be living
- virus genome more similar to host genome than other virus genomes
- almost identical to host genome in some groups
Iwanoski
first to isolate virus in 1892
tobacco mosaic virus
virus classifications
- host range
- size
- structure
- virus life cycle
host range
- viruses infect all organisms
- usually adapted to one species or related species
size
smaller than ribosomes
structure
- nucleic acid
- capsid
- animal viruses have envelope outside capsid
nucleic acid in viruses
can have DNA or RNA
single or double strand
1 piece or more than 1 piece
capsid
protein container enclosing nucleic acid
- helical, rod, tobacco mosaic virus
- polyhedral, 20 sided, adenovirus, cold virus
- complex, tail, head, sheath, bacteriophage
animal virus external envelope
-outside capsid
-derived from host membrane
HIV, flu
-envelope allows virus to merge with membrane when entering and leaving the host
virus life cycle
- virus binds host membrane
- virus releases nucleic acid into host cell
- new virus nucleic acids and virus proteins synthesized in host
- new capsids assemble around nucleic acids
- new viruses released from host cell
- some kill host cell as new viruses are released
- enveloped virus- leaves host cell without killing host
cell
3 virus groups
- DNA viruses (bacteriophages)
- RNA viruses
- retroviruses (RNA)
Bacteriophage
DNA virus
infects E. coli
viral DNA injected into host
lytic and lysogenic life cycles
more bacteriophages on body than all other cell types combined
ex: Corynebacterium, Vibrio, Clostridium botulinum
lytic cycle
virulent
produces new viruses and kills host and then infects other cells
lysogenic life cycle
viral DNA incorporated into host DNA and replicated with host DNA as host divides
all resulting cells contain viral DNA and express the viral toxin
the bacteriophage infection makes non-pathogenic bacterial disease causing toxins cause symptoms
more bacteriophages on body than all other cell types combined
RNA virus
8 RNA strands
influenza
RNA virus enzyme
RNA replicase (RNA dependent RNA polymerase) copies virus RNA into more virus RNA NO DNA and NO transcription- genetic information already in RNA form
RNA virus presentation
respiratory infection often followed by secondary bacterial infections; pneumonia
spread by respiratory droplets and fomites (contaminated objects)
influenza envelope
2 surface spike protein patterns (H and N)
spikes allow virus to bind, enter and exit host
spike variation determines______
capsid antigen characteristics (A, B or C)
antigenic shift
recombines RNA from human, pig or bird flu strains
RNA from different species combined into new influenza virus in host
preformed antibodies may still function
most severe
antigenic drift
variation from random point mutations
only a few amino acids changed
preformed antibodies may still function
not as severe
influenza A
most common, most severe form
cause of pandemics in 1918, 1957, 1968, 1977
Spanish flu
avian flu
H7H9, H5N1, H7N7
infection in poultry in Asia and Africa
60% fatality rate
H3N2
human flu
H1N1, H2N2
swine flu
Retrovirus
2 RNA strands
Retrovirus enzyme
reverse transcriptase
copies RNA into DNA
HIV
Human Immunodeficiency Virus
- binds CD4 receptors on T4 helper cells and macrophages
- structure changes to reduce antibody response
- moves inside T4 cells
- RNA converted to DNA by reverse transcriptase
- virus DNA inserts into host DNA
- may remain inactive but usually produces and releases new viruses that infect other cells
- T4 count falls
- body cannot produce enough new T4 cells
- indicates onset of AIDS
- HIV destroys immune system and death results from secondary infection
secondary infection/ diseases related to HIV
Pneumocystis carinii
Toxoplasma
Mycobacterium tuberculosis
Karposi’s sarcoma
HAART
Highly Active Antiretroviral Therapy
drug cocktails
drug cocktail effects
reduce virus to low levels
maintain T4 helper cell number
reduce resistance of viruses to treatment
treatment targets on HIV
- interfere with reverse transcriptase
- fusion inhibitors
- integrase inhibitors
- protease inhibitors
- block virus assembly
treatments that interfere with reverse transcriptase
inhibit DNA synthesis from RNA
AZT
mimics thymine nucleotides
produces non-functional DNA
fusion inhibitors
prevents virus entry into host membrane
protease inhibitors
prevent modification of HIV proteins
integrase inhibitors
prevent HIV DNA from inserting into host DNA
HIV treatment drawbacks
high cost
toxic side effects
may not completely remove virus`
why some HIV is a “long term non progress or”
weaker virus
abnormal receptors on T4 cells
Hepatitis
targets liver
fecal/oral transmission
many strains, syndromes, outcomes
Hepatitis A
infectious hepatitis RNA contagious before symptoms appear survives for days on surfaces resistant to bleach 1/3 Americans have antibodies form Hep A
Hepatitis A passive vaccine
effective within 2 weeks of exposure
protection lasts six months
Hepatitis A active vaccine
(developed in) 1995 (?)
Hepatitis B
chronic hepatitis
liver cancer
DNA
transmission similar to HIV- infected blood, blood products, IV drug use, unsafe sex
Hepatitis B active vaccine
for newborns and children
Hepatitis B passive vaccine
reduces severity of infection after exposure to hep B
Hepatitis C
chronic RNA no vaccine similar transmission to HIV higher fatality rate than HIV main reason for liver transplant
Rhabdovirus
rabies
ssRNA
rhabdovirus reservoir
mammals (not rodents)
rhabdovirus transmission
bites
travels along nerves to brain
rhabdovirus infection
40 day incubation time
causes encephalitis
usually fatal within a few days of onset of symptoms
hydrophobia
painful muscle spasms from swallowing water
contractions of jaw muscles
furious rabies
biting maintains virus in animal populations
polio virus
ssRNA
poliomylelitis strains 1, 2, 3
human only host
inhibits motor neurons in cord
polio transmission
fecal/oral
stable in swimming pools, lakes, drinking water, food
only 1% becomes paralytic
Salk vaccine
first active vaccine
antigens for all 3 polio strains
inactive virus so requires boosters
used to vaccinate children
Sabin vaccine
oral vaccine
attentuated (living) providing long lasting immunity
80 polio cases in secondary contacts since 1980
post polio syndrome
muscle weakness that occurs later in life as nerves become inhibited
herpes simplex 1
oral herpes
herpes simplex 2
genital herpes
human papilloma virus
many strains
some cause cervical cancer
Ebola
Africa
fruit bat reservoir
incurable
90% fatality rate
west Nile virus
bird reservoir
mosquito vector
f
Viroids
infectious RNA molecules
only infect plants
potato spindle tuber, cadang/cadang
prions
infectious proteins that infect brain
no cure
prion infection
eating meat contaminated with CNS tissue
slow acting with long incubation time
not destroyed by high heat
prion effect
convert normal proteins in brain to prions
prions are a misfiled form of normal protein (beta sheet, prion PrP)
scrapies
prion in sheep
bovine spongiform encephalopathy
mad cow disease
sheep to cow, cow to cow, cow to human
Creutzfeldt Jacob disease
human for of mad cow
Kuru
related to cannabalism
chronis wasting disease
deer and elk
Viruses and cancer
cause 20-25% of cancers
HIV- Karposi’s sarcoma
HPV- cervical cancer
