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44 Cards in this Set
- Front
- Back
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Picornaviruses Capsid coat serves multiple functions
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-Protects the viral RNA genome from degradation
-Being non-enveloped makes the picornaviruses very hardy (Both within the environment and within the host - RNAses, Acid, Alcohols ) -Determines host/tissue tropism |
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Picornaviruses life cycle big picture
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rapid (~8hr)
-cytoplasmic -lytic (except HAV |
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Life cycle of the picornaviruses 1
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1. Entry
2. Genome is released 3. Vpg Removed RNA is translated 4. Polyprotein Cleavage (assemble on membrane) 5. Replication 6. Particle assembly 7. Particle release |
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Picornaviruses replication is 2 folds.
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RNA viral comes in, host ribosome makes a minus strand intermediate. The this negative strand is converted into positive strand for genome synthesis, translation, template for a negative strand for packaging.
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Three medically important groups of viruses that gain access to the human body through the GI tract
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Enteroviruses-do not cause diarrhea
Rotaviruses ((Gastroenteritis) Caliciviridae ( (e.g. Norwalk) (Gastroenteritis)) |
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Enterovirus Transmission
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Fecal-Oral Route
Majority of virus shed is founds in the feces. Only minor amounts in Respiratory Secretions (e.g. saliva/nasal mucus) |
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Enteroviruses are Highly Communicable
and Typically People Become Infected via: |
Close personal contact (e.g. household, diapers)
Contaminated surfaces (e.g. drinking glass, telephone) Contaminated Food or Water |
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Enterovirus Pathogenesis
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- Enter via the GI Tract
- Replicate in the upper respiratory tract and underlying lympathics - Primary (minor) viremiaReplicates in target tissue 2nd (major) viremia |
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Enterovirus infections in the blood (primary viremia) are Most often
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because at
this point it is contained by host immune defense mechanisms |
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What determines disease in enteroviruses pathogenesis?
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Target tissue
determines disease Recall: 2nd tissue is determined by capsid receptor binding specificity |
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Incidence of Enteroviral Infections
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So by far the most common human viral infectious agent
Based on prevalence of antibodies, we know enteroviruses are are distributed worldwide Virtually everyone has antibodies by age 5 Overall incidence is unknown because most infections are asymptomatic |
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Everyone is at risk of enteroviruses infections because
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Survive well in warm moist environments
- year round in hot countries - seasonal (summer/fall) in temperate climates |
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Clinical manifestations of enteroviruses infections varies according to
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Gender
- Some Enteroviruses of the CNS affect boys more often than girls - Some studies suggest that after puberty, reverse is true (might be related to fact that historically women likely had more exposure to children) Age Children more susceptible - probably because they are less likely to have cross reacting antibodies from previous exposures |
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Polioviruses is epidemic in areas like china, cote d'ivoire and endemic in others like Chad, DR Congo, Pakistan and afganistan because of
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Poor hygiene
Lack of vaccination |
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The most common cause of viral rash is
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Enteroviruses Also present with respiratory tract infection, fever
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Carditis, pericarditis can be caused by enteroviruses but especially
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Coxsachieviruses B (Cox B)
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Aseptic Meningitis is
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Acute fever,
Meningeal irritation, neck stiffness Headache & Rash (low WBC count) and can be caused by cox a,b and Echo |
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Acute flaccid paralysis
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AFP-often used to describe sudden
weakness or paralysis caused by Cox A, B and Echo |
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A patient shows with herpangina, hand and foot and mouth disease, respiratory tract infection, fever and rash
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Cox A.
Herpangina Characteristic discrete, painful, vesicles on the pharynx & soft palate |
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COX a infections also develop eye problems such as
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acute hemorrhagic conjunctivitis
(second or third day) |
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Cox B outbreaks occur mostly in
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Neonatal disease
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A patient with Pleurodynia (Skeletal Muscle)
(fever & chest pain)(abdomin if diaphragm), diabetes, pancreatitis and orchitis (swelling of testicles) can have |
Cox B
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Patient with fever, respiratory tract infection, encephalitis, meningitis and paralytic disease can have
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poliovirus
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There are 4 outcomes to poliovirus infection
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Asymptomatic
Abortive Poliomyelitis (resp infex) Nonparalytic Poliomyelitis Paralytic Disease |
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CNS (meninges)
- Back pain & stiffness muscle spasms - Resolves 2-10 days |
Nonparalytic
Poliomyelitis (1-2%) |
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Infects neurons
(motor & autonomic, not sensory) Causes necrosis |
Paralytic Disease (0.1-2%)
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Poliovirus Paralytic Manifestations
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Asymmetrical flaccid paralysis without sensory loss
lower motor neurons - Degree varies - Can be progressive - Possible outcomes: Complete recovery Residual paralysis |
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Bulbar Poliomyelitis
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Pharynx, vocal cords
- Respiration paralysis Iron Lung |
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Postpolio Syndrome
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- No virus present
- Deterioration of original muscles affected Believed to be due to loss of neurons Post polio syndrome possible most common in the clinics |
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Enterovirus Infection Diagnosis can be difficult because it affects many people, collection sample and there is limitations of methods, However under some circumstances a presumptive diagnosis can be made with some degree of certainty
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Pronounced seasonality in temperate latitudes
Tendency for community outbreaks |
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Enteroviruses lab sample collection
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Sample multiple sites to optimize the opportunity to recover a virus
Throat swab, rectal swab, stool specimen, blood cerebrospinal fluid, pericardial fluid, tissue depending on the clinical syndrome Late in the course of illness - feces because at this time the lower intestine may be the only site where virus is still being excreted |
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The best diagnostic tool to identify enteroviruses is
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Originally - Nucleic Acid Hybridization
Currently - Universal Pan-EV PCR - Polio serotypes-specific PCR (VP1) New Trend - Genomic Sequencing 5’UTR Capsid (VP1) antigenic regions |
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Non-Polio Enterovirus Treatment
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Currently no non-polio enterovirus vaccine
Experimental vaccines in trial Treatment is symptom-management Several possible future treatments options Interferon, Ribavirin, Antibodies Piravir© (Pleconaril) Binds to pocket in VP1 (capsid protein) & prevents the virus from entering the host ce |
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Enterovirus Infection Prevention
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Good Hygiene
Covering mouth & nose when coughing or sneezing WASH HANDS |
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Someone not vaccinated against poliovirus can be given
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- Prophylactic Immunoglobulin
Paralytic polio protection for a few weeks Effective if given before infection No value once the clinical symptoms develop |
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Poliovirus trivalent vaccines (Salk (IPV), Sabin (OPV)
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prevent against all 3 types of serotypes
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Salk IPV Vaccine characteristics
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Killed (formlin inactivated)
Considered MOST safe because it is inactivated HIGHLY EFFECTIVE (recently made more immunogenic) >90% immune after 2 doses >99% immune after 3 doses LESS Convenient: 4 injections over 2 years (2m, 4m, 6-18m, 4-6yrs) Minimum Interval 4 wks |
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Sabin OPV Vaccine characterisitcs
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LIVE, attenuated virus
Passaged in cell culture Not considered as Safe because replicates HIGHLY EFFECTIVE >50% immune after 1 dose >95% immune after 3 doses IgM & IgG in blood plus IgA in intestine VERY Convenient Herd Immunity |
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Salk IPV Vaccine advantages
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Stable
Safe for immunocompromised No risk of vaccine disease No risk of spread |
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Salk IPV Vaccine disadvantages
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Antibody response not as robust
Booster needed Requires sterile syringes and needles Injection is painful No herd immunity |
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Sabin OPV Vaccine effective
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Full antibody response
No booster needed Inexpensive and easy (oral) Herd immunity |
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Sabin OPV Vaccine disadvantages
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Risk of vaccine induced Polio
Risk of spread to immunocompromised Spread without consent |
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Poliovirus Vaccination United States
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Only IPV is available in the United States
Schedule begun with OPV should be completed with IPV Any combination of 4 doses of IPV and OPV within 5 years constitutes a complete series |
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USA Poliovirus Vaccination Who should be vaccinated
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Routine childhood vaccination is recommended
Exceptions: Anyone with life-threatening allergic reaction to neomycin, streptomycin or polymyxin B Anyone who has had a severe allergic reaction to a polio shot Anyone moderately or severely ill should wait Adults at increased risk Travelers to polio is epidemic or endemic. Members of communities with wild type polio disease Laboratory workers Health-care workers Adults whose children will be receiving the OPV |
