''Bunyavirales'' is an order of segmented negative-strand RNA virus
es with mainly tripartite genomes. Member viruses infect arthropod
ns, and vertebrate
It is the only order in the class ''Ellioviricetes''.
The name ''Bunyavirales'' derives from Bunyamwera
where the original type species
'' was first discovered.
''Ellioviricetes'' is named in honor of late virologist Richard M. Elliott
for his early work on bunyaviruses.
Bunyaviruses belong to the fifth group of the Baltimore classification system
, which includes viruses with a negative-sense
, single-stranded RNA genome. They have an enveloped
, spherical virion. Though generally found in arthropod
s or rodents, certain viruses in this order occasionally infect humans. Some of them also infect plants.
In addition, there is a group of bunyaviruses whose replication is restricted to arthropods and is known as insect-specific bunyaviruses.
A majority of bunyaviruses are vector-borne. With the exception of Hantaviruses
es, all viruses in the ''Bunyavirales'' order are transmitted by arthropods
(mosquitos, tick, or sandfly). Hantaviruses are transmitted through contact with rodent
feces. Incidence of infection is closely linked to vector activity, for example, mosquito-borne viruses are more common in the summer.
Human infections with certain members of ''Bunyavirales'', such as ''Crimean-Congo hemorrhagic fever orthonairovirus
'', are associated with high levels of morbidity and mortality, consequently handling of these viruses is done in biosafety level 4
laboratories. They are also the cause of severe fever with thrombocytopenia syndrome
es are another medically important member of the order ''Bunyvirales''. They are found worldwide, and are relatively common in Korea
, western North America and parts of South America. Hantavirus infections are associated with high fever, lung edema, and pulmonary failure. The mortality rate varies significantly depending on the form, being up to 50% in New World hantaviruses (the Americas), up to 15% in Old World hantaviruses (Asia and Europe), and as little as 0.1% in Puumala virus
(mostly Scandinavia). The antibody reaction plays an important role in decreasing levels of viremia
is somewhat similar to that of the ''Paramyxoviridae
'' family; ''Bunyavirales'' form enveloped, spherical virions with diameters of 80–120 nm
. These viruses contain no matrix proteins.
Bunyaviruses have bi- or tripartite genome
s consisting of a large (L) and small(s), or large (L), medium (M), and small (S) RNA segment. These RNA segments are single-stranded, and exist in a helical formation within the virion. Besides, they exhibit a pseudo-circular structure due to each segment's complementary ends. The L segment encodes the RNA-dependent RNA polymerase
, necessary for viral RNA replication and mRNA synthesis. The M segment encodes the viral glycoprotein
s, which project from the viral surface and aid the virus in attaching to and entering the host cell. The S segment encodes the nucleocapsid
Most bunyaviruses have a negative-sense L and M segment. The S segment of the genus ''Phlebovirus
and both M and S segment of the genus ''Tospovirus
'' are ambisense
Ambisense means that some of the genes on the RNA strand are negative sense and others are positive sense. The ambisense S segment codes for the viral nucleoprotein
(N) in the negative sense and a nonstructural protein
(NSs) in the positive sense. The ambisense M segment codes for glycoprotein
(GP) in the negative sense and a nonstructural protein (NSm) in the positive sense.
The total genome size ranges from 10.5 to 22.7 kbp
The ambisense genome requires two rounds of transcription to be carried out. First, the negative-sense RNA is transcribed to produce mRNA and a full-length replicative intermediate. From this intermediate, a subgenomic mRNA encoding the small segment nonstructural protein is produced while the polymerase produced following the first round of transcription can now replicate the full-length RNA to produce viral genomes.
Bunyaviruses replicate in the cytoplasm
, while the viral proteins transit through the ER
and Golgi apparatus
. Mature virions bud from the Golgi apparatus into vesicles which are transported to the cell surface.
Bunyaviruses infect arthropod
ns, and vertebrate
Plants can host bunyaviruses from the families ''Tospoviridae'' and ''Fimoviridae'' (e.g. tomato, pigeonpea, melon, wheat, raspberry, redbud, and rose). Members of some families are insect-specific, for example the phasmavirids, first isolated from phantom midges
and since identified in diverse insects including moths
, wasps and bees
, and other true flies
There are currently 383 virus species recognised in this order.
The phylogenetic tree diagram provides a full list of member species and the hosts which they infect.
The order is organized into the following 12 families:
Diseases in humans
Bunyaviruses that cause disease in humans include:
* California encephalitis virus
, La Crosse encephalitis virus
, Jamestown Canyon virus
and Snowshoe hare virus
vector: mosquitoes Family: Peribunyaviridae
reservoir: small mammals or rodents vector: aerosolized excreta from these mammals Family: Hantaviridae
* Crimean–Congo hemorrhagic fever
reservoir and vector: ticks, amplifying hosts and vector: small mammals, domestic mammals Family Nairoviridae
* Rift Valley fever
reservoir: bats vector: mosquitoes amplifying hosts: small mammals, domestic mammals Family: Phenuiviridae
* Bwamba Fever
reservoir: monkeys vector: mosquitoes, amplifying hosts: donkeys Family: Peribunyaviridae
* Severe fever with thrombocytopenia syndrome
* Lassa fever
and Argentine hemorrhagic fever
reservoir: rodents vector: aerosolized excreta from these mammals Family: Arenaviridae
Bunyaviruses have segmented genomes, making them capable of rapid recombination and increasing the risk of outbreak. The bunyavirus that causes severe fever with thrombocytopenia syndrome
can undergo recombination both by reassortment of genome
segments and by intragenic homologous recombination
. Bunyaviridae are transmitted by hematophagous arthropods including mosquitoes, midges, flies, and ticks. The viral incubation period is about 48 hours. Symptomatic infection typically causes non-specific flu-like
symptoms with fever lasting for about three days. Because of their non-specific symptoms
, Bunyavirus infections are frequently mistaken for other illnesses. For example, Bwamba fever is often mistaken for malaria.
Prevention depends on the reservoir, amplifying hosts and how the viruses are transmitted, i.e. the vector, whether ticks or mosquitoes and which animals are involved. Preventive measures include general hygiene, limiting contact with vector saliva, urine, feces, or bedding. There is no licensed vaccine for bunyaviruses. As precautions Cache Valley virus and Hantavirus research are conducted in BSL-2 (or higher), Rift Valley Fever virus research is conducted in BSL-3 (or higher), Congo-Crimean Hemorrhagic Fever virus research is conducted in BSL-4 laboratories.
1940s: Crimean–Congo hemorrhagic fever
is discovered in Russia
1951: 3,000 cases of Hantavirus
were reported in South Korea in 1951, a time when UN forces were fighting on the 38th parallel during the Korean War
1956: Cache Valley virus
isolated in ''Culiseta inornata
'' mosquitoes in Utah
1960: La Crosse virus
was first recognized in a fatal case of encephalitis in La Crosse, Wisconsin
1977: Rift Valley Fever
virus caused approximately 200,000 cases and 598 deaths in Egypt
2017: Bunyavirales order is created
Viralzone: BunyaviridaeBunyaviridae Genomes
mdash;database search results from thViral Bioinformatics Resource CenterVirus Pathogen Database and Analysis Resource (ViPR): Bunyaviridae