[W10] Bunyaviruses

Question 1

What type of genome do Bunyaviruses have?

Answer 1

Negative-sense or ambisense, single-stranded RNA (ssRNA), segmented into 3 parts (S, M, L)

Question 2

How many genome segments do Bunyaviruses have and what are they called?

Answer 2

3 segments – Small (S), Medium (M), and Large (L)

Question 3

Where does Bunyavirus replication and assembly take place?

Answer 3

In the cytoplasm; assembly and maturation occur at the Golgi complex

Question 4

What size are Bunyavirus particles?

Answer 4

80–120 nm in diameter

Question 5

What protein does the S segment encode?

Answer 5

Nucleocapsid protein (N) and sometimes NSs (non-structural, interferon antagonist)

Question 6

What proteins are encoded by the M segment?

Answer 6

Glycoproteins Gn and Gc, and NSm (non-structural protein involved in budding)

Question 7

What is encoded by the L segment?

Answer 7

The L protein, an RNA-dependent RNA polymerase

Question 8

What are the functions of Gn and Gc proteins?

Answer 8

Envelope glycoproteins responsible for cell entry via receptor binding and fusion

Question 9

What is the role of NSs protein?

Answer 9

Inhibits host interferon responses and promotes immune evasion

Question 10

What does the NSm protein do?

Answer 10

Plays a role in virion assembly and morphogenesis

Question 11

What is the genome organisation of Bunyamwera virus?

Answer 11

S (~961 nt) encodes N; M (~4458 nt) encodes Gn, Gc, NSm; L (~6875 nt) encodes L

Question 12

What is the typical coding strategy for Bunyaviruses?

Answer 12

Negative-sense, but some genera (e.g., Phlebovirus) use ambisense coding

Question 13

What are the key steps in the Bunyavirus replication cycle?

Answer 13

Attachment → Entry → Uncoating → Transcription → Translation → Replication → Assembly → Release

Question 14

How do Bunyaviruses enter host cells?

Answer 14

Receptor-mediated endocytosis, followed by low pH-induced fusion in endosomes

Question 15

What is ‘cap-snatching’ in Bunyavirus transcription?

Answer 15

The viral polymerase cleaves 10–18 nucleotides from host mRNAs to prime viral mRNA synthesis

Question 16

What is the order of RNA synthesis in Bunyaviruses?

Answer 16

First antigenome (+RNA), then genome (–RNA)

Question 17

What happens during viral morphogenesis?

Answer 17

Viral glycoproteins and RNPs assemble at the Golgi and bud into vesicles for release

Question 18

What mechanisms drive Bunyavirus evolution?

Answer 18

High mutation rate (quasispecies), reassortment, and rare recombination

Question 19

What is reassortment in Bunyaviruses?

Answer 19

The mixing of RNA segments between viruses during co-infection, creating new strains

Question 20

Name three viral families within the Bunyavirales order.

Answer 20

• Hantaviridae
• Nairoviridae
• Phenuiviridae

Question 21

What disease is caused by Hantavirus and how is it transmitted?

Answer 21

HFRS or HPS, transmitted via contact with rodent excreta

Question 22

What is the vector and fatality rate of CCHFV?

Answer 22

Transmitted by Hyalomma ticks, with a fatality rate up to 40%

Question 23

What is Rift Valley Fever Virus (RVFV) and its primary vectors?

Answer 23

A zoonotic virus spread by mosquitoes (Aedes, Culex); affects humans and livestock

Question 24

What is unique about Oropouche virus (OROV)?

Answer 24

Causes urban outbreaks in South America, transmitted by midges and mosquitoes

Question 25

What type of virus is Schmallenberg virus (SBV) and who does it affect?

Answer 25

An Orthobunyavirus; affects cattle and sheep, causing fever and fetal deformities

Question 26

What is the primary replication strategy of ambisense Bunyaviruses?

Answer 26

Encode one gene in each strand direction; require replication before full transcription

Question 27

What consensus sequences are found at the genome ends of Orthobunyaviruses?

Answer 27

Highly conserved UTR sequences at 5′ and 3′ ends essential for replication

Question 28

How do Bunyaviruses avoid the host immune response?

Answer 28

Via NSs protein that suppresses interferon signalling

Question 29

How is CCHFV diagnosed and treated?

Answer 29

ELISA, RT-PCR; supportive care and sometimes ribavirin (no approved vaccine)

Question 30

What vaccine types are used for RVFV?

Answer 30

Inactivated and live-attenuated vaccines (mainly for animals)

Question 31

How are Bunyavirus glycoproteins processed?

Answer 31

Synthesised in the ER, glycosylated, and transported to the Golgi for assembly

Question 32

Why is RVFV a concern for public health?

Answer 32

Causes severe disease in humans and livestock, potential for outbreaks in new regions

Question 33

What is the function of the nucleocapsid (N) protein?

Answer 33

Binds viral RNA to form ribonucleoprotein complexes (RNPs) for replication and packaging

Question 34

How is the L protein recruited for replication?

Answer 34

Co-packaged with RNPs; catalyses both transcription and replication in the cytoplasm

Question 35

Which Bunyavirus is most linked to agricultural economic loss?

Answer 35

Rift Valley Fever Virus (RVFV) due to livestock abortion and death

Question 36

What plant-infecting genus belongs to Bunyavirales?

Answer 36

Tospoviruses (e.g., Tomato spotted wilt virus – TSWV)

Question 37

What is the role of the Golgi in Bunyavirus assembly?

Answer 37

Site of virion budding and glycoprotein accumulation before release

Question 38

What are the main diagnostic methods for Bunyavirus infections?

Answer 38

ELISA, RT-PCR, viral culture (in high biosafety labs)

Question 39

What key cellular receptors have been implicated in Bunyavirus entry?

Answer 39

* DC-SIGN * L-SIGN * Integrins * HSPG

Question 40

Why are Bunyaviruses considered emerging threats?

Answer 40

High mutation/reassortment rate, broad host range, climate-driven vector spread