ID1 3 - Picornavirus and Coronavirus PDF

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ID1 3 - Picornavirus and Coronavirus...

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ID1 Lecture 3 – Picornavirus and Coronavirus 

Picornaviruses = small single stranded RNA viruses with naked capsids (very stable and can survive low and high pH conditions, detergents, and mild sewage treatment) o Most common type of viral infections in humans (rhinoviruses > enteroviruses) o Mainly transmitted via fecal-oral route o All are cytopathic = usually kill the cell to release virion particles after viral replication inside a host cell  Exception is Hepatitis A o Picornaviruses that infect humans = “Perch on a PEAK”  P = Poliovirus  E = Enteroviruses, Echoviruses  R = Rhinovirus  C = Coxsackie Virus (A and B)  H = Hepatitis A  Note: all green colored viruses fall under Enterovirus umbrella; Enterovirus is both the name of the genus as well as the name of some of the viruses that fall under the enterovirus genus o Enteroviruses  4 major species = A, B, C, D (all have their own serotypes)  Certain serotypes can cause specific syndromes  Uncommon in young kids; if they do occur, they occur in neonates, older kids, and adults  Young children are the principle reservoirs for enteroviruses  Usually asymptomatic and have not developed hygiene skills  problematic for transmission in places like daycare centers  Syndromes  Neurologic = enteroviruses are leading cause of aseptic meningitis  Cardiac = can cause myocarditis, pericarditis, dilated cardiomyopathy resulting in permanent defects like abnormal EKGs, cardiomegaly, and heart failure  Pleurodynia (aka Bornholm’s Disease aka Myositis) = rapid onset acute chest pain mostly caused by Coxsackie B virus; no long term effects  Herpangina = Vesicles or nodules on soft palate of mouth causing pharyngitis; mostly caused by Coxsackie A virus  Exanthems = rashes typically caused by Enteroviruses  Hand, Foot, and Mouth Disease = usually caused by Enterovirus 71 or Coxsackie A9, A16  Neonatal disease caused by Enterovirus can be highly severe and fatal o Poliovirus Pathogenesis  Mostly asymptomatic by nature, but very severe when symptomatic  Summer-fall transmission and enters via oral-fecal route (because it’s an enterovirus)  Infection begins in pharynx and small intestines and replicates in tonsils and Peyer’s patches in the GI tract  From lymph tissue the virus can enter systemic circulation (viremia)  can occupy anterior horn of the spinal cord  targets the brain and meninges  destroys alpha motor neurons  muscular weakness and even paralysis (poliomyelitis)  Poliomyelitis = rare complication of polio that can come in several forms based off of severity  Abortive poliomyelitis = very non-specific findings like fever, malaise, headache, sore throat, vomiting  Non-paralytic poliomyelitis = can result in aseptic (aka viral) meningitis (inflammation of meninges)  Paralytic poliomyelitis = rarest form o Flaccid asymmetric paralysis = only motor neurons are affected (not sensory)

Spinal polio = infection limited to the spinal cord Bulbar polio = infection reaches the pharynx, larynx, vocal cords  affects breathing and is associated with high mortality rates (75%)  Post-Polio Syndrome aka Post-Polio Muscular Atrophy  Polio virus destroys motor neurons to muscle  muscle weakness and paralysis  Unaffected motor neurons can take over function, but they are working overtime  30-40 years later  50% of former polio sufferers develop post-polio syndrome  Post-polio syndrome = condition characterized by the originally affected muscle undergoing atrophy  Not a re-emergence of the poliovirus as its been long gone  Salk and Sabin Vaccines for Polio Treatment  Occasional polio epidemics (outbreaks) in the US, but is in general very well controlled o Due to re-activation of the polio virus in the Sabin vaccine  In India, Central Asia, and Africa polio is considered an endemic (disease is mainly restricted to these regions of the world)  Polio (like small pox) doesn’t have an animal reservoir  easier to eradicate  Salk Vaccine = recommended vaccine; consists of inactivated (killed virus) o Requires multiple doses o Can prevent polio disease, but not infection and subsequent disease transmission  Sabin Vaccine = live attenuated virus (virus that has been genetically modified and protects against viral infection and transmission of the disease to others) o Requires only one dose o Elicits greater immune response than Salk vaccine o Not used in US because polio has largely been eradicated and using live virus has the risk of the virus mutating toward a virulent form  transmission to other people Rhinoviruses  Typically localized to the upper respiratory tract (optimal temp = 33 C)  Peaks in spring and fall  Has 50% infection rate in families  Virion particles travel through aerosols (coughing, sneezing), nasal secretions, and fomites  Sensitive to pH (can target cells this way)  Do not cause asthma, but can exacerbate asthma symptoms in diagnosed asthmatics  Responsible for majority of common colds  Colds take about a week to clear up  Interferon can provide transient protection  INflmamation and edema 2-3 days post-infection is possible  Secondary bacterial infections like otitis media and sinusitis can occur  No specific vaccines or antiviral therapies currently available because there are 3 species of Rhinoviruses (HRA, B, and C) with over 100 different serotypes o o

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Sensitive to acidic pH Route Optimal growth temp Target Organ Mode of Cell Entry Associated with Incidence

Enterovirus No Fecal/oral, respiratory 37 C GI, CNS, Heart At cell surface Variable: none to paralysis (polio) Summer/fall peaks

Rhinovirus Yes Respiratory 33 C Nasal Epithelium Triggered by acidic pH Asthma exacerbation, common cold Spring and fall peaks

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Coronavirus o Enveloped viruses  unstable (sensitive to detergent) and need to remain wet (can’t dry out)  Simply washing your hands will kill coronaviruses o Contain the largest viral RNA genome o Located in upper respiratory tract and GI tract o The spikes that come off of the membrane allow binding to target cells o Re-infection is likely because IgA response is short-lived (not efficient enough to eliminate it) o No vaccines or antiviral therapies available for humans o Operate best in the winter o Symptoms are relatively minor, but associated with SARS (Sudden Acute Respiratory Syndrome) and MERS (Middle East Respiratory Syndrome) viruses  Also 2nd leading cause of the common cold o SARS  Primary animal reservoir is hypothesized to be bats  Bats infected civets which were then eaten by local residents in China  The virus was then transmitted through aerosol droplets  SARS virus spike proteins mutated to allow the virus to bind with more efficiency to ACE-2 receptors in humans  human to human transmission was made possible...