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Microbiology- Virology
Reoviruses, Rhabdoviruses, and Rubiviruses (T Pierce)
36
Medical
Professional
11/27/2009

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Cards

Term
Characteristics of reoviruses
Definition
  • aka rotavirus
  • dsRNA viruses
  • two major human infections
    • rotavirus infection (infantile gastroenteritis)
    • colorado tick fever (self limited, febrile illness)
Term
structure/genetics of rotavirus
Definition
  • dsRNA non enveloped
  • looks like a hubbed wheel (rota = wheel)
  • 11 discrete segments that can reassort and each encodes a protein
  • large enteric virus
    • outer capsid (VP4 and VP7)
    • inner capsid (VP6)
    • 7 Ag groups (A, B, C in humans with A being the most common)
      • B,C not usually seen in North America
  • viruse encodes enterotoxin
Term
pathogenesis of rotavirus
Definition
  • fecal oral transmission
  • first infection btw 3-24 mnths
  • prior to 3 months maternal Ab or factors in milk are protective
  • life cycle
    1. virus binds to enterocyte receptor (receptor with higher density in younger children)
    2. replicates in intestinal epithelial cells
    3. viron must become activated in cell cytoplasm by protein cleavage of capside proteins
    4. uncleaved virions do not initiate replication
    5. activated virions replicate and assemble in cytoplasmic inclusions
    6. complete virons bud into ER
    7. envelope is lost after cell release (lysis)
Term
Describe immunity and potential for reinfection of rotaviruses
Definition
  • type specific immunity
  • re-infections can occur but are usually asymptomatic
    • G1 type VP7 accounts for most types or rotovirus
Term
epidemiology of rotavirus
Definition
  • most common cause of severe diarrhea in young children
  • first infection btw 3-24 months
  • cause 20% of all diarrheal deaths in children under 5
  • oubreaks in child care centers
  • nosocomial infections in children's hospitals
  • annual peak of infection in winter
    • peak season (60% of all kids admitted)
  • northeast wave- late summer, see cases in southwest and as months proceed by winter, it moves up to DC and New England and Canada
Term
clinical manifestations of rotavirus
Definition
  • rotavirus diarrhea associated with high fever, vomitting, and resp. tract symptoms
  • more likely result in severe dehydration
  • more than 20 diarrhea stools or vomitting episodes in 24 hrs
  • some children with fever and vomitting without diarrhea
  • most have transient rise in hepatic enzymes
Term
complications and fatalities of rotavirus
Definition
  • cause- dehydration, electrolyte imbalance, and acidosis
  • risk factor: malnutrition
  • in immunocompromised hosts (ex: AIDS, DiGeorge's) demonstrates virus in liver and kidney
  • possible cause of pneumonia
  • intussusception
  • SIDS
Term
dx, tx of rotavirus
Definition
  • dx
    • commercial assay for group A specific Ag detection
    • stool EM
    • electropherotyping
  • tx
    • no antivirals
    • support for dehydration
Term
second generation rotaviruses vaccine
Definition
  • Rotateq
    • pentavalent
    • for human VP7 gene (G1-4)
    • first dose 6-12 weeks subsequent doses at 4-10 week intervals
  • rotarix
    • oral two dose live vaccine
    • single human strain G1
    • introduced in latin america
Term
colorado tick fever virus (epidemiology, clinical manifestations)
Definition
  • zoonosis of rodents
  • causes viremia, infects immature RBC's
  • acute disease
    • headachge
    • fever
    • myalgia
    • but SUBCLINICAL INFECTION
    • leukopenia
    • thrombocytopenia
  • transmitted by Dermacenter ticks
Term
structural/genetic characteristics of rubella
Definition
  • aka german measles
  • + ssRNA genomre
  • single Ag type
  • childhood infection
  • congenital infection
  • only member of rubivurs genus within togavirus family
Term
acquired rubella (german measles) (clinical manifestations, transmission)
Definition
  • transmission- aerosolized particles
  • infectivity from nasopharynx virus shedding
  • contagious period 5 days before till 6 days after rash
  • incubation period: 14-21 days
  • characteristic clinical findings
    • fever, arthralgias, sore throat
    • rash
      • face spreading downward
      • erythematous maculopapular
    • suboccipital adenopathy
Term
lab dx of rubella
Definition
  • virus isolation RARELY done
  • rubella specific IgM
  • more than 4 fold increase in IgG paired sera (acute and convalescent)
Term
congenital rubella (clinical manifestation/ characteristics)
Definition
  • persistent, progressive infection
  • fetal and placental infection occurs in first trimester maternal infection 
  • risk of infection and subsequent congenital defects is inversely related to gestational age
    • fetal infection rates of 90% in first trimester
  • virus induced progressive necrotizing vasculitis
  • parenchymal hypoplasia
  • extensive involvement of multiorgan
Term
classic congenital rubella infection clinical manifestations
Definition
  • hepatosplenomegaly
  • thrombocytopenic purpura
  • dermal erythropoiesis (blueberry muffin)
  • low birthweight
  • end organ damage
    • heart (PDA)
    • eye (cataracts and retinopathy)
    • auditory (deafness)
    • brain (microcephaly, autism)
Term
rubella vaccine (type of injection, type of vaccine, side effects)
Definition
  • subQ injection
  • part of MMR
  • live attenuated vaccine prepared in human diploid fibroblasts
  • works by elicigting neutralizing Ab
  • common side effect: mild rubella
  • eliminated in US
Term
types of rhabdoviruses
Definition
  • rabies (genus: lyssavirus)
  • vesicular stomatitis virus (genus: vesiculovirus)
Term
characteristics/structure/genetics of rabies/ lyssavirus
Definition
  • enveloped virus
  • type 1 is classic rabies (see type 4-6 in human cases as well)
  • type 5 is european
  • bullet shaped
  • five structural proteins
  • ss (-) RNA
  • G protein spike that binds to cells
  • replicate and assemble in cell cytoplasm
Term
rabies (mechanism of transmission, reservoirs)
Definition
  • transmission via animal to human which causes acute encephalitis
    • exposure to saliva
    • virus in saliva attaches to peripheral nerve endings and travels to the brain
  • in nature, rabies is disease of mammals (reservoirs)
    • canines (virtually elim. in US)
    • racoons
    • mongooses
    • skunks
    • bats (causes most US cases)
  • human rabies almost always secondary to animal bite
    • rare exposure through inhalation or transplatation of corneas
    • worldwide the major reservoir is dog
Term
rabies: clinical signs
Definition
  • attacks nerves
  • moves up spinal cord to brain
  • this cause agitation, dementia, paralysis, and death
Term
rabies genome
Definition
  • G: enveloped glycoprotein
  • M- matrix envelope protein
  • L- large, replicase
  • N- nucleoprotein
  • NS(P)- nonstructural protein
Term
replication of rabies virus
Definition
  • enter cells by attaching to nicotinic ACh R followed by fusion event
  • replication of virus in cytoplasmic inclusions (called Negri bodies)
  • replicase copies ss (-) RNA produce ss + RNA than produce ss (-) RNA
  • genes expressed in descending order
Term
different methods of transmission of rabies
Definition
  • dogs (India, other developing countriews)
  • wild animals
  • bats (most common cause of transmission in US)
    • usual leave unperceived bite sleeping persons
  • vehicle is infected animal saliva
    • bite or scratch or mucous membrane
    • inhalation
    • transplantation of cornea
Term
cellular pathogenesis of rabies
Definition
  1. after tissue exposure, rabies virus G protein attach to gangliosides on neuronal cells
  2. nicotinic ACh R
    • peripheral N's and ascending at 100 mm/day
    • CNS directly by aerosol into neuroepithelial cells of olfactory end organ
    • no viremia
  3. spinal ganglia, virus replicates and spreads from cell to cell from spinal cord to brain
  4. minimal brain histologic damage in stark contrast to severity of clinical rabies
  5. Negri bodies = eosinophilic inclusions of rabies virus Ag's
Term
rabies pathology process
Definition
  1. incubation period (5 dys-2 yrs)
  2. prodrom (0-10 days)
  3. acute neurological (2-7 days)
  4. corna (5-14 days)
  5. death
Term
describe virus assembly that occurs at negri bodies with rabies
Definition
  • virus assembly points within infected cell are called Negri bodies
  • final envelopment (budding) will occur at the plasma membrane
Term
epidemiology of human rabies
Definition
  • most cases in India
  • mostly seen in children, majority male (rural boys in summer months)
  • in US, most human rabies from bats
  • most cases unperceived bites in sleeping individuals
  • aerosol route in caves frequented by bats
Term
rabies: clinical manifestation stages
Definition
  1. assymptomatic phase
  2. nonspecific illness
  3. brain infection
  4. paralytic form after bat exposure mimicing Gillian Barre
  5. coma
  6. death via respiratory arrest or myocarditis
Term
rabies: clinical manifestations in asymptomatic phases
Definition
  • prodromal period (2-10 days)
  • viral invasion of CNS
Term
rabies: clinical manifestation in nonspecific illness stage
Definition
  • can be resp. and GI
  • behavioral and emotional changes
  • limbic system, spinal cord, brain stem
  • local pruritis, pain, paresthesia at inoculation site
Term
rabies: clinical manifestations in brain infection
Definition
  • furious or hyperactive form
  • aggressive (bittting, hitting, yelling)
  • hyperactivity
  • hallucinations
  • triggered by sensory stimuli
  • half experience hydrophobia or aerophobia
    • violent diaphragmatic contractions
    • exaggerated protective reflex
Term
dx of rabies
Definition
  • often misdx clinically
  • CSF show signs of meningoencephalitis
  • RT-PCR performed on saliva
  • rabies specific Ab in serum or CSF measured by rapid fluorescent focus inhibition test
  • Ab detected 6 days of onset of symptoms
Term
modern concepts of rabies immunology
Definition
  • relies of Ab to G protein of viral envelop
  • Ab appear 7-14 dys after first dose
  • booster dose at 21 days required
  • with IM vaccination- 4 doses in first 2 weeks and 5th dose at 28 days or later
  • intradermal regimes use muliple sites (2-8) administered on 4-5 occasions between days 0-90
  • HIV infected patients respond poorly
  • subjects older than 50 respond less well
  • uncertain role of cellular immunity
  • molecular mimicry of nicotinic R binding motife between rabies G protein and HIV gp120 leads to false positive HIV tests
Term
immunization schedules for postexposure
Definition
  • rabies immune globin (RIG) on day 0
  • cell culture vaccine on each of the days (0, 3, 7, 14, 28)
  • 1 mL of vaccine is administered in deltoid
  • in developing countries, this is not always practical
    • intradermal to increase volume with fewer doses
  • adverse rxns
    • fevere
    • HA
    • insomnia
    • palpitations
    • diarrhea
  • sensitization to proteins in older nerve tissue vaccines leads to allergic encephalomyelitis
Term
enzootic forms of rabies in north america
Definition
  • racoon- east US
  • skunk- midwest
  • skunk- cali
  • coyote- south TX, mexican border
  • fox- SW, mexico border
  • fox- northern NE, Canada
Term
ways to contain rabies
Definition
  • vaccination of domestic animals
  • reduce spread of wild animals
    • experimental bait vaccines (foxes, racoons, coyotes) 
      • oral vaccinations
    • eradicate infected animals
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