Yellow fever virus
Yellow fever virus
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- Yellow fever virus (YFV) is the prototype member of the approximately 75 viruses of Flaviviridae family; "flavus" derives from the Latin word for yellow.
- Mosquito vector
- YFV first isolated in 1927.
- There is 1 serotype with 7 distinct genotypes.
- South America: 2 genotypes
- Africa: 5 genotypes
- Single-stranded RNA virus with an 11 kilobase genome composed of 3 parts:
- 5’ non-coding region
- a single open reading frame (ORF) which encodes 3 structural and 7 non-structural proteins
- Capsid (C)
- Membrane (prM)
- Envelope (E): This is the main structural protein
- Mediates virus entry into the cell via clarathrin-dependent endocytosis
- Non-Structural (NS): NS1, NA2a, NS2b, NS3, NS4a, NS4b, and NS5 are involved in:
- RNA replication
- Post-translational clevage of the viral polyprotein
- 3’ non-coding region
- Cell targets
- Virus introduced by blood-feeding mosquito into the epidermis where resident dendritic cells (DC) are the principle target for early virus replication.
- Toll-like receptors (TLRs) on the surface of DC are key in the critical role of sensing microbial stimuli.
- DCs initiate and modulate the adaptive immune system.
- DCs carry the virus via lymphatics to draining lymph nodes and subsequently to the bloodstream with eventual dissemination to cells in the liver, spleen, remaining lymph nodes, kidneys and heart.
- Immune evasion
- Inhibition of the innate interferon type I response is key
- Non-human primate studies have demonstrated down-regulation of 43 genes associated with innate immunity, including
- Interferon gamma receptor-1
- CD83, a marker of DC maturation
- TNFSF11: though to induce DCs to stimulate naive T cell proliferation
- Pro-inflammatory mediators are significantly higher in patients with fatal illness when compared with survivors including:
- Tumor necrosis factor-alpha (TNF-α)
- Interleukin-6 (IL-6)
- Interleukin-1 receptor antagonist (IL-1RA)
- Interferon-gamma inducible protein 10 (IP-10)
- Monocyte chemoattractant protein-1 (MCP-1)
- Similar findings were seen in rhesus macaques, the animal model for studying many aspects of yellow fever virus infection
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