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Zika virus (strain Mr 766)

VIRION

Enveloped, spherical, about 50 nm in diameter. The surface proteins are arranged in an icosahedral-like symmetry.

GENOME

Monopartite, linear, ssRNA(+) genome of of 10,794 bp. The genome 5’ end has a methylated nucleotide cap for canonical cellular translation. The 3’ terminus is not polyadenylated but forms a loop structure. This secondary structure leads to the formation of a subgenomic flavivirus RNA (sfRNA) through genomic RNA degradation by host XRN1. sfRNA is essential for pathogenicity, and may play a role in inhibiting host RIG-I antiviral activity as shown for Dengue virus

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and the viral messenger RNA. The whole genome is translated in a polyprotein 3,419 aa long, which is processed co- and post-translationally by host and viral proteases.

REPLICATION

CYTOPLASMIC in mammals, NUCLEAR in insects?

  1. Attachement of the viral envelope protein E to host receptors mediates internalization into the host cell by apoptotic mimicry
  2. Fusion of virus membrane with host endosomal membrane. RNA genome is released into the cytoplasm.
  3. The positive-sense genomic ssRNA is translated into a polyprotein, which is cleaved into all structural and non structural proteins (to yield the replication proteins).
  4. Replication takes place at the surface of endoplasmic reticulum in cytoplasmic viral factories. A dsRNA genome is synthesized from the genomic ssRNA(+).
  5. The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
  6. Virus assembly occurs at the endoplasmic reticulum. The virion buds via the host ESCRT complexes at the endoplasmic reticulum, is transported to the Golgi apparatus.
  7. The prM protein is cleaved in the Golgi, thereby maturing the virion which is fusion competent.
  8. Release of new virions by exocytosis.

Geography

Global map of Zika virus infection source



healthmap

Human cases (source )

First report: 1947 in Uganda on a Rhesus monkey

LocationYearReported Human casesEstimated HumancasesSeroprevalence
1952Uganda 6.1%
1963Indonesia 13%
1964Uganda1
1975Nigeria2
1977-78Indonesia17
1999Ivory coast1
2007Micronesia, Yap185 73%
2010Cambodia1
2013Australia1 (imported)
2013Indonesia1
2013-14New-Caledonia32
2013-14French Polynesia8,51029,000
2014New-Caledonia114
2015South America?>1.5 million

Disease

Case fatality rate: <0.001%. Seven death were related to Zika virus infection in Brazil in december 2015, for more than 1 million estimated cases
Incubation in Humans: 82 hours