Togaviruses

fackrel@uwindsor.ca

toga.ppt

Toga Viruses

• Structure

• Classification

• Multiplication

• Clinical manifestations

• Epidemiology

• Diagnosis

• Control

Baron’s Web Site

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

+ ssRNA

Rubella: Classification

• Family Togaviridae

• genus Rubivirus only member

• single serotype

• three structural polypeptides

Unlike other Togaviruses rubella is not arthropod borne

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

USA data

Alphavirus

Encephalitis

Sindbis

Alphaviruses are arthropod borne (arboviruses)

Alphavirus: Structure

• icosahedral 40-50 nm

• enveloped

• attachment glycoprotein

• ss RNA, sense, monopartite

Alphavirus: Classification

• common envelope glycoprotein

• common capsid antigenic sites

• 26 antigenic types

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