1. Picornavirus
Pico + RNA = Picorna

2. Genome is an mRNA. (+ sense) Naked genome is sufficient for infection.
Virion is a naked, small (25 to 30 nm) icosahedral capsid enclosing a single-stranded positive RNA genome.
Enteroviruses are resistant to pH 3 to pH 9, detergents, mild sewage treatment, and heat.
Rhinoviruses are labile at acidic pH; optimum growth temperature is 33° C.
Genome is an mRNA. (+ sense)
Naked genome is sufficient for infection.
Virus replicates in cytoplasm.
Viral RNA is translated into polyprotein, which is then cleaved into enzymatic and structural proteins.
Most viruses are cytolytic
Box Unique Properties of Human Picornaviruses

3. Picornaviridae Enterovirus Poliovirus types 1, 2, and 3
Coxsackie A virus types 1 to 22 and 24
Coxsackie B virus types 1 to 6
Echovirus (ECHO virus) types 1 - 9, ,
Enterovirus 68 to 71 and 73 to ….
Parechovirus (formerly echovirus 22,23)
Kobuvirus: Aichi virus and Ljungan virus
Hepatovirus
-Hepatitis A virus
Rhinovirus types 1 to 100+
Animal viruses:
Cardiovirus
Aphthovirus ….
Body_ID: B056001

7. eIF4G cleaved  cellular protein synthesis is shut off

8. Kozak sequence (NNNPuNNAUGG )
The initiation AUG codon in the polio virus open reading frame is preceded by eight other AUGs.
RCCAUGG
RYYAUGG (R = purine, Y = pyrimidine);

9. Disease Mechanisms of Picornaviruses
Enteroviruses enter via the oropharynx, intestinal mucosa, or upper respiratory tract and infect the underlying lymphatic tissue; rhinoviruses are restricted to the upper respiratory tract
In the absence of serum antibody, enterovirus spreads by viremia to cells of a receptor-bearing target tissue
Different picornaviruses bind to different receptors, many of which are members of the immunoglobulin superfamily (i.e., ICAM-1)
The infected target tissue determines the subsequent disease
Viral, rather than immune, pathologic effects are usually responsible for causing disease symptoms
The secretory antibody response is transistory but can prevent the initiation of infection
Serum antibody blocks viremic spread to target tissue, preventing symptoms
Enterovirus is shed in feces for long periods
Infection is often asymptomatic or causes mild, flulike or upper respiratory tract disease
Body_ID: B056003

11. Epidemiology of Enterovirus Infections Disease/Viral Factors
Nature of disease correlates with specific enterovirus and age of person
Infection often asymptomatic, with viral shedding
Virion resistant to environmental conditions (detergents, acid, drying, mild sewage treatment, and heat)
Transmission
Fecal-oral route: poor hygiene, dirty diapers (especially in daycare settings)
Ingestion via contaminated food and water
Contact with infected hands and fomites
Inhalation of infectious aerosols
Body_ID: B056004
Body_ID: PB056004

12. Who Is at Risk? Modes of Control
Young children: at risk for polio (asymptomatic or mild disease)
Older children and adults: at risk for polio (asymptomatic to paralytic disease)
Newborns and neonates: at highest risk for serious coxsackievirus and enterovirus disease
Geography/Season
Viruses have worldwide distribution; wild-type polio virtually eradicated in developed countries because of vaccination programs
Disease more common in summer
Modes of Control
For polio, live oral polio vaccine (trivalent OPV) or inactivated trivalent polio vaccine (IPV) is administered
For other enteroviruses, no vaccine; good hygiene limits spread
Body_ID: B056004
Body_ID: PB056004

15. Poliovirus infection
Asymptomatic illness results if the viral infection is limited to the oropharynx and the gut. At least 90% of poliovirus infections are asymptomatic.
Abortive poliomyelitis, the minor illness, is a nonspecific febrile illness occurring in approximately 5% of infected people. Fever, headache, malaise, sore throat, and vomiting occur in such people within 3 to 4 days of exposure.
Nonparalytic poliomyelitis or aseptic meningitis occurs in 1% to 2% of patients with poliovirus infections. In this disease, the virus progresses into the central nervous system and the meninges, causing back pain and muscle spasms in addition to the symptoms of the minor illness.

16. Paralytic polio, the major illness, occurs in 0. 1% to 2
Paralytic polio, the major illness, occurs in 0.1% to 2.0% of persons with poliovirus infections and is the most severe outcome. It appears 3 to 4 days after the minor illness has subsided, thereby producing a biphasic illness. In this disease, the virus spreads from the blood to the anterior horn cells of the spinal cord and to the motor cortex of the brain. The severity of paralysis is determined by the extent of the neuronal infection and by which neurons are affected. Spinal paralysis may involve one or more limbs, whereas bulbar (cranial) paralysis may involve a combination of cranial nerves and even the medullary respiratory center.
Paralytic poliomyelitis is characterized by an asymmetrical flaccid paralysis with no sensory loss. Poliovirus type 1 is responsible for 85% of the cases of paralytic polio. Reversion of the attenuated vaccine virus types 2 and 3 to virulence can cause vaccine-associated disease.

19. Coxsackievirus and Echovirus Infections

20. Herpangina Type A 1-10 Type B 1-5 Echoviruses
Mostly in children; epidemicin summer months
Abrupt fever, sore throat, anorexia, abdominal pain and vesicles on soft palate, pharinx and tonsills

21. Hand-foot-and-mouth disease
Coxsackie A16, 4, 5, 10

22. Myocardial and pericardial infections
Coxsackie B, echovirus
Sudden onset Diabetes: Coxsackie B 4

23. Viral (aseptic) meningitis
Coxsackie A, B
Echovirus
Summer and fall

24. Fever, rash, and common coldlike symptoms
Summer minor illnes:
Rubelliform rush on face, neck and chest
Accompanied by fever
No distinctive feature
Short duration

25. Plerodynia Coxsackie B Sudden chest pain, fever, malaise
(Abdominal or testicular pain)

26. Laboratory Diagnosis CSF findings Culture
Molecular and serological methods

27. Treatment and Prevention
Vaccine available only for Polio

29. Rhinoviruses Advantages and Disadvantages of Polio Vaccines
Epidemiology of Rhinovirus Infections
Disease/Viral Factors
Virion is resistant to drying and detergents
Multiple serotypes preclude prior immunity
Replication occurs at optimum temperature of 33° C and cooler temperatures
Transmission
Direct contact via infected hands and fomites
Inhalation of infectious droplets
Who Is at Risk?
People of all ages
Geography/Season
Virus found worldwide
Disease more common in early autumn and late spring
Modes of Control
Washing hands and disinfecting contaminated objects help prevent spread
Vaccine
Advantages
Disadvantages
Live (oral polio vaccine)
Effective Lifelong immunity Induction of secretory antibody response similar to that of natural infection Spread of attenuated virus circulating to contacts promotes indirect immunization (herd immunity) Inexpensive and easy to administer No need for repeated booster vaccine
Risk of vaccine-associated poliomyelitis in vaccine recipients or contacts; spread of vaccine to contacts without their consent Not safe for administration to immunodeficient patients
Inactivated polio vaccine
Effective Good stability during transport and in storage Safe administration in immunodeficient patients No risk of vaccine-related disease
Lack of induction of secretory antibody Booster vaccine needed for lifelong immunity Requires sterile syringes and needles Injection more painful than oral administration Higher community immunization levels needed than with live vaccine
Vaccine
Advantages
Disadvantages
Live (oral polio vaccine)
Effective Lifelong immunity Induction of secretory antibody response similar to that of natural infection Spread of attenuated virus circulating to contacts promotes indirect immunization (herd immunity) Inexpensive and easy to administer No need for repeated booster vaccine
Risk of vaccine-associated poliomyelitis in vaccine recipients or contacts; spread of vaccine to contacts without their consent Not safe for administration to immunodeficient patients
Inactivated polio vaccine
Effective Good stability during transport and in storage Safe administration in immunodeficient patients No risk of vaccine-related disease
Lack of induction of secretory antibody Booster vaccine needed for lifelong immunity Requires sterile syringes and needles Injection more painful than oral administration Higher community immunization levels needed than with live vaccine
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