| MicrobiologyBytes: Virology: Bunyaviruses | Updated: September 11, 2007 | Search |
BunyavirusesMicrobiologyBytes: Latest Updates
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Enveloped, spherical particles, 80-120nm diameter.
Single-stranded (-)sense RNA; segmented - each virion contains 3 molecules:
L ~8.5kb / L, other ?
M ~5.7kb / G1, G2, NSM
S ~0.9kb / N, NSSAll 3 RNA species are linear, but in the virion, appear circular because the ends are held together by base-pairing. Not present in equimolar amounts! 5' ends not capped; 3' ends not polyadenylated; genomic RNA not infectious.
Phleboviruses & Tospoviruses: Differ from the other three genera (Bunyavirus, Nairovirus, Hantavirus) in the following respect: Genome segment S organization is different - AMBISENSE - 5' end is (+)sense, 3' end (-)sense:
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Similar to Orthomyxoviruses:
i) Virus polymerase (L protein) copies genome to form:
a) mRNA encoding N protein - 5' m7G cap is obtained by cannibalizing host
cell mRNAs - like influenza.
b) (+)sense intermediate
ii) (+)sense intermediate is copied by L protein to form new genomic RNA.
iii) Virus buds into Golgi vacuoles - released when cell lyses (c.f. Toga's - bud from plasmalemma, Flavi's - bud into undifferentiated cytoplasmic vacuoles).
Phleboviruses: follow same basic strategy, but there are 2 rounds of transcription (one before, one after the formation of a 'reverse-sense' RNA intermediate) to cope with the ambisense coding strategy:
The bunyavirus NSs protein is an interferon antagonist, functionally equivalent to the influenza NS1 and filovirus VP35 proteins.
Rift Valley Fever: First isolated from sheep in E.Africa 1930. In man, produces an acute, 'flu-like illness. Transmitted by mosquitoes from animal reservoirs (e.g. sheep) to man leads to EPIZOOTICS. In the 1990s there have been massive outbreaks of R.V.F. In sub-Saharan Africa - millions of people infected, attack rates of up to 35% - more mosquitoes, more people or more domestic animals?
Outbreak of Rift Valley Fever in Northeastern Kenya, 1997-98: 27,500 infections, 170 deaths - the largest recorded outbreak of RVF in East Africa.
Hantavirus genus: Spread from rodents (reservoir) to man by aerosolized faeces, not insect vector, causing hantavirus pulmonary syndrome. These are important emergent viruses.
CDC: All About Hantavirus
Of
Mice, Men, and Microbes: Hantavirus
by David R. Harper, Andrea S. Meyer, Robert R. Parmenter.
© MicrobiologyBytes 2004.