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picornavirus (virion nucleic acid)
single (+) stranded RNA
picornavirus (nucleocapsid structure)
picornavirus (virion nucleic acid structure)
single stranded;
one molecule per virion;
(+) stranded
picornavirus (summary of replication)
1) Viral RNA enters the cytoplasm of the host cell and functions *first* as mRNA
2) virion mRNA is translated into a large polyprotein
3)the poly proteins are cleaved into functional proteins (including viral RNA polymerase and capsomeric proteins)
4) the polymerase uses the virion RNA as template to make complementary minus-stranded RNA
picornavirus (examples)
[Enteric Viruses:
polio virus
Human Enteroviruses
(formerly classified as:
Coxsackie viruses
ECHO viruses)
Hepatitis A]

Rhinoviruses (NOT ENTERIC, aerosol/resp. droplets)
Aseptic Meningitis (caused by what virus group/type(s))
Coxsackie virus
ECHO virus
POLIO (virus group)
virus group: PICORNAVIRUS (polio virus)
POLIO (epidemiology)
fecal-oral transmission

epidemics not seen until 20th century (rise in sanitation), in prevaccine era most people were exposed w/in first year of life, aquired passive--> active immunity
sanitation improved, not everyone infected in infancy, susceptible population developed, when poliovirus introduced to susceptible population epidemic of paralytic disease resulted
as sanitation further improved, epidemics became more severe because older children and adults are more likley to become paralyzed
POLIO (pathogenesis)
a) virus swallowed
b) initial multiplication in lymphoid tissues w/ oral and fecal excretion of the virus
c) in rare cases tha end in paralysis: invasion of CNS (probably by way of VIREMIA)
d) circulating Ab appears too late to prevent invasion of CNS, paralysis occurs despite large amounts of Ab against virus in the blood
e) incubation period: 2-3 weeksPOL
POLIO (diagnosis)
isolation of virus (via specific inoculation of cell culture)
or rise in antibody titer
POLIO (vaccination)
both killed and live attenuated have bee used (both induce humoral Antibodies)

killed vaccine is now preferred (since the only cases of paralytic disease in the US in recent years have been back-mutations of vaccine)
POLIO (chemotherapy)
Coxsackie virus (virus group)
Coxsackie virus (epidemiology)
fecal-oral, but also respiratory aerosols
POLIO (clinical presentations)
a) Subclinical (inapparent) infection
b) Mild/Nonspecific
c) Aseptic Meningitis (non-paralytic polio)
d) Paralytic Polio
1. SPINAL POLIO (destruction of motor neurons)
2. BULBAR POLIO (attack on the respiratory centers in the medulla and cranial nerves)
caused by what virus?
mode of transmission?
common where?
Some Group B Coxsackie viruses (picornaviruses)

generalized infection (not just heart)
enteric epidemiology
generally newborn nursery epidemic
(also in adults)
caused by what type of virus?
probable cause of symptoms?
caused by Group B Coxsackie viruses (bening, self-limiting picornavirus)

characterized by thoracic pain aggravated by deep breaths

probably caused by viral attack upon intercostal muscle cells
caused by what type of virus?
caused by Group A Coxsackie Viruses (picornaviruses)

symptoms: acute sore through with other systemic signs of infection

characteristic ulcerating vesicles in the throat
caused by Group A Coxsackie viruses

spread by fecal-oral pathway
VIREMIC disease
vesicular lesions all appear at about the same time
Rhinoviruses (virus group)
Rhinoviruses (epidemiology)
aerosol, respiratory droplet transmission
(NOT enteric, because they are labile at pH 3 of the stomach and grow poorly at core body temperature (37 degrees)-- grow best at 33 degrees
Rhinoviruses (pathogenesis)
-entry through upper respiratory tract
-stays upper Respiratory Tract (doesn't grow well at higher temps)
-immunity via nasal/secretory IgA
Rhinovirus (diagnosis)
virus can be isolated from nasal secretions in cell culture
Rhinovirus (vaccine)
immpractical, too many different serotypes
Rhinovirus (therapy)
high doses Vit. C
Reoviruses (nucleic acid)
double stranded RNA (dsRNA)
multiple molecules (~10 different segments)
Reoviruses (nucleocapsid symmetry)
Reoviruses (replication)
1) reovirus virion RNA first functions as a template for synthesis of mRNA
2) polymerase that makes this mRNA is part of the virion (contrast to polymerase of poliovirus)
3) More viral RNA polymerase is made in infected cells (*note: because the "original" polymerase protein is essential, the RNA of reoviruses is NOT infectious)
compare RNA polymerase of:
poliovirus virion: contains only a gene for its RNA polymerase

reovirus virion: contains RNA polymerase AND the actual polymerase protein (RNA OF REOVIRUS IS NOT INFECTIOUS)
rotoviruses (group)
rotaviruses (epidemiology)
fecal-oral pathway

most kids infected by age 2
rotaviral diarrhea is a major cause of infant mortality in developing coutnries
rotavirus (vaccine)
new live attenuated vaccines (an effective oral vaccine was withdrawn <1 year after licensing, because of association with intestinal obstruction)
adenoviruses (nucleic acid)
dsDNA viruses
adenoviruses (nucleic acid structure)
single molecule of linear dsDNA
adenoviruses (nucleocapsid symmetry)
adenoviruses (replication)
assembled in the nucleus

viral mRNA and protein synthesis are regulated (not made in 1:1 ratio like picornavirus mRNA:protein)

only adenovirus proteins needed early in infection are made early (early mRNA)

mRNA for virion (structural) proteins is only made late in infection, after viral DNA synthesis has begun

controlled expression of viral genes is characteristic of all DNA viruses
adenoviruses (epidemiology)
airborne (virions are stable when dried, can cause kerato-conjunctivitis and common colds)

enteric fecal-oral (the enteric adenoviruses, cause gastroenteritis and diarrhea)
conjuntivitis (is caused by what types of viruses?)
adenoviruses, various enteroviruses
gastroenteritis (caused primarily by what type of viruses?)
enteric adenoviruses
Norwalk virus (a calciviris)
Norwalk virus (virus group)
calcivirus (nucleic acid)
single molecule of + stranded RNA
Characteristics of enveloped viruses
1. NUCLEOCAPSID coated with a lipoprotein MEMBRANE
2. Infectivity of enveloped viruses is destroyed by treatment with ether (does not harm other simple nucleocapid viruses, eg. polio)
3. Generally unstable; transmission requires close contact
4. Pattern of assembly more complicated than unenveloped viruses
Characteristics of enveloped virus assembly
Pattern of assembly more complicated than unenveloped viruses:

a) few cell-associated virions at anytime

b) continuous release of virions w/o gross cellular damage (cell may ultimately die)

c. use of MODIFIED CELLULAR MEMBRANE (that is one containing GLYCOPROTEINS within the envelope membrane of the virion)
Stages in release of an enveloped virus:
-normal cell membrane
-modified cell membrane and intracellular nucleo-capsid (capsomers and nucleic acid are not shown)
- stages in viral release by budding through the modified membrane

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