Lec 20 - Vector borne viral infections Flashcards
Compare the genome structure and overall size of alpha and flaviviruses, and bunyaviruses.
Alpha and flaviviruses = enveloped spherical circular (+) ssRNA genome and smaller size
Bunyaviruses = enveloped segmented circular (-) ssRNA genome and larger size
Describe the steps in an alphavirus replication cycle.
- E1 and E2 glycoproteins bind receptor
- Clathrin mediated endocytosis
- Non-structural proteins translated from full length RNA
- Structural proteins translated from sgRNA
- Nucleocapsid assembly
- pE2, 6k and E1 insert into ER and move to membrane by secretory pathway
List clinical presentations of alphavirus infection.
Fatigue, fever, rash, myalgia, arthralgia, photophobia, headaches, nausea, oedema, sore throat, encephalitis, bleeding gums
What is the classification of CHIKV and how is it transmitted?
- Alphavirus of Togaviridae
- Enveloped (+) ssRNA genome, T = 4
- Transmitted by Aedes mosquitos of africanus, aegypti and albopictus species
Which Aedes mosquito species carries a CHIKV variant? What is this mutation?
- Albopictus species = Indian Ocean lineage
- Increased infectivity and transmission from mutated envelope protein
What is the pathogenesis of CHIKV in terms of incubation, symptoms, complications, treatments and immune response patterns?
- Incubation = 4-7 days
- Symptoms = fever, severe arthralgia for months
- Complications = chronic rheumatoid arthritis, meningoencephalitis, cardiac, GI tract and neurological problems
- Treatment = only symptomatic
- Immune patterns = type 1 IFNs peak at 3-5 days, adaptive develops, symptoms become undulating peaks after main infection
What is the classification of Ross River Virus and where did it originate from?
- Alphavirus, Togaviridae
- Enveloped (+) ssRNA genome
- Endemic in Australia, Papua New Guinea and South Pacific Islands from Ross River in Townville
How is Ross River Virus transmitted and what are the symptoms?
- Transmission = macropod-mosquito cycle with rodents and horses as amplifiers
- Mosquitos = Culex annuliorstris, Aedes vigilax, Aedes notoscriptus
- Symptoms = 70% asymptomatic, acute febrile illness then arthralgic disease as endemic polyarthritis
What is the classification, symptoms and transmission of Barmah Forrest Virus?
- Classification = Alphavirus, Togaviridae, enveloped (+) ssRNA genome
- Symptoms (mimics RRV) = polyarthritis, arthralgia, myalgia, rash
- Transmission = mosquito-mammalian cycle with Culex annulirostris, Aedes vigilax, Aedes normanensis and Aedes notoscriptuscan
Describe the structure of Flaviviruses.
- Lipid enveloped (+) ssRNA genome
- C, prM and E structural proteins
- E protein = antigenic determinant tethered to viral membrane
- Single ORF
Describe the replication of Flaviviruses in terms of entry, location of replication and location of assembly.
- Clathrin mediated endocytosis
- Replicate on host membranes reorganised by viral non-structural proteins
- Assemble in ER
What are the 2 categories of symptoms from Flavivirus infection? Give examples of each.
- Visceral = hepatitis, haemorrhage
- Neurotrophic = encephalitis, congential illness
- Can also be asymptomatic
What is the classification and transmission of DENV?
- Flavivirus, Flaviviridae
- Enveloped (+) ssRNA virus, T = 3
- Primates-mosquito sylvatic cycle; human-mosquito epidemic cycle
Describe the typical course of acute DENV infection including incubation time and serology features.
- Incubation = 5 days
- Viraemia peaks with fever from microvascular permeability with risk of shock/haemorrhage
- IgM and IgG production
Describe a secondary heterologous DENV infection.
- Shorter viraemia from cross-reactive antibodies
- Cross-reactive memory T cells creates an earlier and stronger response
