Picornaviruses are among the most diverse (more than 200 serotypes) and 'oldest' known viruses (temple record from Egypt ca. 1400 B.C.).
FMDV was one of the first viruses to be recognized - Loeffler and Frosch 1898.
Poliomyelitis as a viral disease was first recognized by Landsteiner and Popper, 1909 (though the virus was not isolated until the 1930's. Name: 'Pico (Greek = very small) RNA Viruses'.
Classification + sense RNA viruses Porcine teschovirus Teschovirus Aichivirus Kobuvirus Equine rhinitis B virus Erbovirus Human parechovirus Parechovirus Hand foot and mouth virus O Aphtovirus Encephalomyocarditis virus Cardiovirus Human Rhinovirus Rhinovirus Hepatitis A Hepatoviruses Poliovirus, Enterovirus, Coxsackie,Echovirus Enteroviruses Picornaviridae Species Genus Family
The genome consists of one s/s (+)sense RNA molecule of between 7.2kb (HRV14) to 8.5kb (FMDV).
Genomic RNA is infectious (~1x106-fold less infectious than intact particles, although infectivity is increased if the RNA is introduced into cells by transfection) - CHARACTERISTIC OF (+)SENSE RNA VIRUSES !!!
There is a long (600-1200 base) untranslated region at the 5' end (important in translation, virulence and possibly encapsidation and a shorter 3' untranslated region (50-100 bases) - important in (-)strand synthesis.
The 5' UTR contains a 'clover-leaf' secondary structure known as the IRES: Internal Ribosome Entry Site
The rest of the genome encodes a single 'polyprotein' of between 2100-2400 aa's.
Both ends of the genome are modified, the 5' end by a covalently attached small, basic protein VPg (~23 AA's), the 3' end by polyadenylation (polyadenylic acid sequences are not genetically coded, there is a 'polyadenylation signal' upstream of the 3' end as in eukaryotic mRNAs):
VP1 (receptor binds) VP4 (virion weakened) release of genome binds to ribosomes polyprotein containing all viral protein sequences is synthesized within 10-15 mins of infection polyprotein is cleaved by viral protease viral RNA-dependent RNA polymerase generates a negative strand RNA template from which the new mRNA/genome and templates can be synthesized.
VP0,VP1,VP3 are cleaved and assembled into subunits 5 subunits into protomer and 12 pentamers to form procapsid genome is inserted into procapsid VP0 cleaved into VP2 and VP4 to complete capsid and the viron is released from the cell.
~1-2h Sharp decrease in cellular macromolecular synthesis; margination of chromatin (loss of homogeneous appearance of nucleus) ~2.5-3h Start of viral protein synthesis; vaculoation of cytoplasm, beginning close to nucleus & spreading outwards ~3-4h Permeabilization of plasma membrane ~4-6h Virus assembly in cytoplasm (crystals sometimes visible) ~6-10h Cell lysis; release of virus particles
Species: Serotypes: Bovine enterovirus 2 Human enterovirus A (coxsackie A viruses) 10 Human enterovirus B (coxsackie B viruses, echoviruses) 36 Human enterovirus C (coxsackie A viruses) 11 Human enterovirus D 2 Poliovirus 3 Porcine enterovirus A 1 Porcine enterovirus B Unassigned: 22
Transmission Human Fecal Matter Hand Sewage Solid waste landfills Water supply Shellfish
Viral replication is iniated in the mucosa,lymphoid tissue of tonsils and pharynx, peyer’s patches primary viremia spread of virus to receptor bearing target tissue 2nd phase of replication signs and symptoms secondary viremia
Clinical forms: 1.Assymptomatic illness- 90% - infection is limited to nasopharynx and GIT 2. Abortive (minor illness)- 5% - non specific febrile - fever,vomiting,malaise,sore throat within 3-5 days of illness
Clinical forms: 1.Herpangina- virus can be recovered from the lesions and feces 2. Hand foot and mouth disease- A16 3.Pleurodynia (Bornholm’s Disease)- Devil’s grip 4. Myocardial and Pleurocardial- 5. Viral (Aseptic )meningitis