2. BUNYAVIRIDAE
Bunyaviruses are a family of viruses that belong to the fifth group of the Baltimore classification
system, which includes viruses with a negative-sense, single-stranded RNA genome.
Bunyaviridae is the largest family of viruses, with over 300 species.
These viruses are generally found in arthropods or rodents.
Certain viruses in this order occasionally infect humans. The bunyaviridae contains five genera:
Orthobunyavirus, Phlebovirus, Nairovirus, Tospovirus, and Hantavirus.
Most of these viruses are transmitted by arthropods (e.g., ticks, mosquitoes, and sand flies) and
cause serious human disease, including certain types of viral hemorrhagic fever.
3. STRUCTURAL CHARACTERISTICS
They have an enveloped virion.
They have spherical virion measuring 90-100nm.
They are ssRNA combined with nucleoprotein.
They contain three segments of negative sense RNA
The two external glycoprotein form surface projection that confer properties of neutralization
of infectivity and hemagglutination of red blood cells.
They have virus-encoded transcriptase present in them
They have a helical and elongated nucleocapsid consisting of a protein shell.
4.
5. LIFE CYCLE
The virus is internalized into the early endosome via endocytosis after the viral glycoproteins bind
to the receptor at the cell surface.
The virus is translocated into the late endosome where the acidic environment triggers a
conformational change in the viral glycoproteins and subsequent membrane fusion.
The viral RNPs (vRNPs) are released into the cytoplasm after membrane fusion. The released vRNPs
move to the rough endoplasmic reticulum (RER) where they direct the synthesis of the viral proteins
via a transcription-coupled translation mechanism.
The vRNP replication process and-The viral RNA (vRNA) in vRNPs directs the synthesis of the
complementary RNA (cRNA), which assembles into complementary RNPs (cRNPs) with the newly
synthesized N proteins and L proteins.
The progeny vRNPs are produced using the cRNPs as the templates.The progeny vRNPs can be used
as templates to produce more vRNPs so that the reproduction process can be amplified. µ and 11
Both the progeny vRNPs and the newly synthesized viral glycoproteins traffic to the Golgi apparatus
where they assemble into progeny virions.
Progeny vRNPs are assembled in the viral tube.The progeny virus buds into the secretory vesicle.
The progeny virions are released outside the cell by exocytosis.
6. BUNYAVIRUS
-California virus
-La crosse virus
-chitto virus
vector-mosquito
Host-rodent ,primate
Ways of transmission –bite of vector
Diseases – fibrile illness, encephalitis ,febrile rash .
Prevention-live attenuated vaccine
PHLEBOVIRUS
-Sandfly fv
-Rift valley fv
Vector-mosquito/phlebotomus
Host-sheep,cattle ,domestic animals
Way of transmission – bite of vector
Disease –febrile illness,seizure,encephalitis ,conjunctivitis etc
Prevention –live attenuated vaccine
7. Nairovirus
-Crimean congo hfv
-Ganjan virus –first isolated in india
Vector-tick
Host – cattle and goats
Ways of transmission –bite of vector
Disease –hemorrhagic fever
Vaccine –killed vaccine.
Hantavirus
-Hantaa virus
-Korean hfv
-Host-rodents
Ways of transmission-inhalation of aerosols from the infected rodents
Disease –pulmonary edema ,respiratory failure
8. Laboratory Diagnosis
Serologic tests used to diagnose bunyavirus infections include the
enzyme-linked immunosorbent assay
,complement fixation
fluorescent antibody
neutralization and hemagglutination inhibition tests.
Knowledge of the geographic site of exposure, season, and presence of arthropods leads to
presumptive diagnosis in febrile cases.
Diagnosis is confirmed by virus isolation, presence of specific IgM, an antibody titer rise in
paired sera, or detection of RNA by reverse transcriptase-polymerase chain reaction (RT-PCR).
9. PREVENTION AND CONTROL
Personal measures, such as the use of proper protective clothing, repellents and bed nets are
effective .
Proper disposal of tires (a breeding site of the mosquito transmitting La Crosse encephalitis
virus) is effective
Rodenticides are used in outbreaks of hemorrhagic fever with renal syndrome.
Rift Valley fever vaccines are used in Africa to immunize sheep and cattle and hence to stop the
transmission cycle to humans.
Medical personnel who care for viremic patients should be careful in handling needles and
surgical instruments to prevent accidental transmission by blood.
Treatment of cases of hemorrhagic fever with renal syndrome during the first week of illness
with ribavirin has proved efficacious
