Classification Multiplication



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Togaviruses

  • fackrel@uwindsor.ca

  • toga.ppt


Toga Viruses



Togaviridiae

  • Rubivirus-rubella

  • Alphavirus- Equine Encephalitis, Sindbis

  • Pestivirus- animal pathogens

    • bovine viral diarrhea, hog cholera


Rubella

  • German Measles

  • (first diagnosed by German doctors)

  • Three day Measles



Rubella: Structure

  • enveloped

  • icosahedral

  • ss RNA sense

  • 40-80 nm

  • 30 nm core

  • hemaglutinin peplomers



Rubella: Classification

  • Family Togaviridae

  • genus Rubivirus only member

  • single serotype

  • three structural polypeptides



Rubella: Multiplication

  • RNA is capped and polyadenylated

  • serves as mRNA -> nonstructural proteins

  • sense RNA -> antisense RNA

  • Antisense RNA template for progeny RNA

  • antisense RNA--> mRNA -> structural proteins

  • mature at intracytoplasmic membranes



Rubella: Clinical manifestations

  • Postnatal

  • rash

  • lymphadenopathy

  • low grade fever

  • Congenital

  • stillbirth

  • spontaneous abortion

  • birth defects



Congential Rubella

  • Ocular- cataracts, retinitis, glucoma ,microphthalmaia

  • Heart defects- patent ductus arteriosis

  • Deafness- cochelar deafness, central auditory imperception

  • CNS- mental retardation, encephalitis, microcephaly

  • Other- hepatitis, pneumonitis



Rubella: Pathogenesis

  • respiratory secretions -direct contact, droplet

  • multiplies in cells of respiratory system

  • extends to lymph nodes, spleen



Rubella: Epidemiology

  • worldwide

  • vaccines licenced 1969

  • no new epidemics

  • incidence ~ 100 /year



Rubella: Host defenses

  • interferon

  • cell mediate immunity

  • neutralizing antibodies

  • hemagglutinin inhibiting antibodies

  • asymptomatic reinfection possible



Rubella: Diagnosis

  • Clinical manifestations- rash, lymphadenopathy

  • Isolate virus respiratory tract

  • Detect Rubella IgM



Diagnosis: Congenital Rubella

  • isolate virus - urine, CSF, blood

  • maternal circulating IgG- lasts 6 months

  • Detect fetal or neonate IgM



Rubella: Control

  • live attentuated rubella vaccine

    • mumps-measles-rubella combination
  • subcutaneous

  • 15 months of age

  • asymptomatic in children

  • mild symptoms in adults



Rubella: Control Strategies

  • 10-20% young women not immunized

  • Therefore immunize

    • college students
    • health care personnel
    • military personnel
    • after childbirth, miscarriage or abortion


Alphavirus

  • Encephalitis

  • Sindbis



Alphaviruses are arthropod borne (arboviruses)



Alphavirus: Structure

  • icosahedral 40-50 nm

  • enveloped

  • attachment glycoprotein

  • ss RNA, sense, monopartite



Alphavirus: Classification



Alphavirus: Multiplication

  • RNA is capped and polyadenylated

  • serves as mRNA -> nonstructural proteins

  • sense RNA -> antisense RNA

  • Antisense RNA template for progeny RNA

  • antisense RNA--> mRNA -> structural proteins

  • mature at intracytoplasmic membranes



Subgenomic mRNA

  • sense strand -> antisense strand

  • 3’ one-third of antisense strand -> mRNA

  • mRNA -> structural proteins



Alphavirus: Clinical manifestations

  • Encephalitis viruses

    • fever, malaise, headache and/or encephalitis
  • Arthritis viruses

    • fever, rash, arthralgia, arthritis


Alphavirus: Epidemiology

  • mosquito-vertebrate-mosquito cycles

  • geographically restricted

  • epizootics- Venezuelan equine enchephalitis

  • urban epidemics- chikungunya virus

  • seasonal



Alphavirus: Diagnosis

  • clincal manifestations

  • known exposure

  • isolate virus

  • detect IgM



Alphavirus: Control

  • reduce mosquito populations

  • vaccinate vertebrate hosts- horses

  • vaccine humans at high risk of exposure




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