Things to Remember about RNA Viruses

  • All RNA viruses are ssRNA except REO is dsRNA
  • All RNA viruses replicate in the cytoplasm except (ORB) ORTHOMYXO, RETRO, and BORNA replicate in the nucleus
  • 3 RNA viruses are non enveloped (PCR), (PCR = PICORNA, CALICI –Noro-, REO)
  • 5 RNA viruses have icosahedral symmetry (PCR + FT), (PCR = PICORNA, CALICI, REO) (FT = FLAVI, TOGA)

Below is a summary of RNA virus families based on criteria for classification and their properties. The details for each RNA virus family will be covered on separate topics.



Family name Rhabdoviridae Retroviridae Orthomyxoviridae Paramyxoviridae Picornaviridae Bunyaviridae Reoviridae Birnaviridae Calciviridae
Genome ss linear RNA, (-) sense Two copies ss linear RNA, (+) sense ss linear RNA, (-) sense, 8 segments ss linear RNA, (-) sense ss linear RNA, (+) sense ss linear RNA, (-) sense, 3 segments ds linear RNA, (+/-) sense, 10-12 segments ds linear RNA, 2 segments ss RNA, (+) sense
Genome size 13-16 kb 3.5-9 kb 13.6 kb 16-20 kb 7.2-8.4 kb 13.5-21 kb 22-27 kbp 7 kbp 8 kb
Symmetry of capsids Helical Icosahedral Helical Helical Icosahedral Icosahedral Icosahedral Icosahedral Icosahedral
Naked or enveloped Enveloped Enveloped Enveloped Enveloped Naked Enveloped Naked Naked Naked
Baltimore class V VI V V IV V III III IV
  Baltimore class III: dsRNA: Have segmented genomes which are transcribed separately to mRNA by viral RNA dependent RNA polymerase packaged within their virions Baltimore class IV: ss (+) RNA viruses: The genome serves directly as mRNA which is translated into early viral proteins used for replicating the viral genome

Ss (+) RNA → mRNA

Baltimore class V: ss (-) RNA: Must synthesize (replication) a complementary + strand which serves as mRNA. Have to carry RNA-dependent RNA polymerase

Ss (-) RNA →cRNA          mRNA

Baltimore class VI: ss (+) RNA: Genomes are (+) sense RNA but unique in that they are diploid and they do not serve directly as mRNA, but as a template for reverse transcription into DNA. DNA integrated into host DNA (Provirus)

RNA               DNA              RNA

Virion 70-85 x 130-380 nm 80-130 nm 90-120 nm 150-300 nm 28-30 nm 90-120 nm 6-80 nm 60 nm 35-40 nm
Virion polymerase + + + + + + +
Genus and species Lyssavirus:

Rabies virus



VSV-New Jersey


Bovine ephemeral fever virus




Jaagsiekte sheep retrovirus







Influenzavirus A

Avian influenza

Equine influenza

Swine influenza

Human influenza

Influenzavirus B

Human influenza

Influenzavirus C

Human influenza



MuV, PIV 5, hPIV2/4a/4b


hPIV1/3, bPIV3








Human enterovirus A, B, C&D, Bovine enterovirus, Porcine enterovirus A&B, Human rhinovirus A&B,


FMDV, Equine rhinitis A virus


LaCrosse encephalitis virus






Hemorrhagic Fever with Renal Syndrome

Hantavirus Pulmonary Syndrome



Mammalian reoviruses type 1, 2, 3

Avian reoviruses


Rotavirus A, B, C, D, E, F



Changuinola virus


Colorado tick fever virus

Disease Rabies is caused by the rabies virus AIDS is caused by HIV1 and HIV2 Influenza A caused by influenza A viruses Newcastle disease caused by NDV FMD caused by FMDV RVF caused by RVFV BT caused by BTV    
Hosts All warm-blooded animals Human Birds, Horse, Pigs, human Avian species cloven-hoofed animals Cattle, goats, sheep, man Cattle, Sheep, goats    
Clinical signs Fever (39-40)        hydrophobia: pharyngeal muscle cramp, dyspnea


Paralytic stage(15-20hs)

– nerve fiber paralysis

respiratory and circulatory failure


Asymptomatic phase 2-15 years (avg. 10)

HIV destroys the immune system

When T4 cell levels fall below 200/mL, AIDS symptoms appear including fever, swollen lymph nodes, diarrhea, weight loss, neurological symptoms, opportunistic infections, and cancers


Fever, headache, cough, sore throat, nasal congestion, sneezing, and body aches

Ocular and/or nasal discharge, dyspnoea, and bloody diarrhea. Central nervous system signs can also occur, including depression or the opposite-hyperexcitability; vestibular or balance problems; tremors, especially of the head and neck; weakness; and partial or total paralysis Blisters inside the mouth that lead to excessive secretion of stringy or foamy saliva and to drooling, and blisters on the feet that may rupture and cause lameness. weight loss no recovery for several months, milk production can decline significantly In animals: Storm abortions, high mortality, high fever, lymphadenitis, nasal and lachrymal discharges, severe prostration, dystocia,

In humans severe influenza-like illness characterized by fever (37.8–40 °C), headache, muscular pain, vomiting, and extreme weight loss


Fever, frothing at mouth, shock, coronitis

Laboratory diagnosis -Antigen detection (IF),

-Negri bodies




ELISA, latex agglutination, and rapid antibody tests Western blot analysis and RT-PCR to rule out false +ves, 2nd tests for –ves (3-6 months later) Antigen detection (ELISA, HI, CF and VNT), Antibody detection (IF),




Virus isolation, ELISA, HI, CF, VNT, RT-PCR

Virus isolation, ELISA, CF, RT-PCR Virus isolation, ELISA, CF, VNT, RT-PCR Virus isolation, IF, Serologic assays (ELISA, latex agglutination)


Target cells  

Neuronal cells

CD4 cells and macrophages with CD4 Epithelial cells Epithelial cells Epithelial cells Hepatic cells, Intestinal epithelial cells    
Cellular Virus receptors  

CD56, p75NTR


CD4, CCR5, and CXCR4

Sialic acids; N-acetylneuraminic acid sialic acid Heparan sulfate, Glycosaminoglycan Cell receptors Sialic acid    
Viral attachment ligand  

RABV G protein



hemagglutinin hemagglutinin Capsid proteins Gn and Gc proteins σ1, JAM-A    
Virus replication Entry via endocytosis, pH-dependent, replication in the cytoplasm, virus assembly by budding from the host plasma membrane Entry via fusion with the cell membrane, pH-dependent, replication, provirus integrates into the host genome in the nucleus Entry via receptor-mediated endocytosis, pH-dependent, replication in the nucleus, assemble in the membrane, release by budding Entry via receptor-mediated endocytosis, pH-dependent, replication in the cytoplasm, assemble in the membrane, release by budding Entry via the receptor, replication in the cytoplasm Entry via receptor-mediated endocytosis, pH-dependent, replication in the cytoplasm, release by budding at Golgi or cell membrane Entry via receptor mediated endocytosis, Acid pH, Proteolytic processing of outer capsid, replication in cytoplasm, exit by lysis    
Transmission A bite from a rabid animal Sexual intercourse Airborne (Inhalation) Direct contact Contact animal to animal, aerosol and fomites Mosquitos bite, eating infected animals Culicoides    
Reservoir host -Wild animals Wild aquatic birds, humans, animals ???      
Vector wild animals and unvaccinated dogs & cats Mosquitoes      
Control Vaccination (cats, dogs, and personnel at risk)

Post-exposure prophylaxis in humans

No vaccine, no cure; therapies slow down the progress of the disease or diminish the symptoms Inactivated virus vaccine, Subunit vaccine, Live, attenuated influenza virus vaccines, Antiviral drugs Hygiene

An inactivated viral vaccine is available

Vaccines are available with no cross-protection

Palliative treatment

Inactivated vaccines are available      


VSV=vesicular stomatitis virus; RSV=Rous sarcoma in chicken; ALV=Avian Leukosis virus; FeLV=Feline leukaemia virus, BLV=Bovine leukaemia virus; HTLV=Human T Cell Leukaemia, HIV=Human immunodeficiency virus, EIAV=Equine infectious anaemia virus; FIV=Feline immunodeficiency virus; CAEV=Caprine arthritis encephalitis virus; AIDS=Acquired immunodeficiency syndrome; MuV=Mumps virus; PIV5=Parainfluenza virus 5 (canine); hPIV2/4a/4b=Human parainfluenza virus type 2, type 4a and 4b; NDV=Newcastle disease virus (avian paramyxovirus 1);  hPIV1/3=Human parainfluenza virus type 1 and type 3; bPIV3=Bovine parainfluenza virus type 3; MeV=Measles virus; CDV=Canine distemper virus; PPRV=Peste-des-petits-ruminants virus; RPV=Rinderpest virus; hRSV=Human respiratory syncytial virus A2, B1, S2; bRSV=Bovine respiratory syncytial virus;  hMPV=Human metapneumovirus; aMPV=Avian metapneumovirus, FMDV=Foot and mouth Disease virus, RVFV=Rift Valley fever virus; CCHFV=Cremian-Congo Haemorrhagic fever virus; NSDV=Nairobi sheep disease virus; AHSV=African Horse sickness virus; BTV=Blue tongue virus




Family name Flaviviridae Togaviridae Coronaviridae Filoviridae Arenaviridae Astroviridae Arteriviridae Toroviridae Bornaviridae
Genome ss linear RNA, (+) sense ss linear RNA, (+) sense ss linear RNA, (+) sense ss linear RNA, (-) sense ss linear RNA, (-) sense, 2 segments ss linear RNA, (  ) ss RNA, (+)   ss RNA, (-) sense
Genome size 10 kb 12 kb 16-21 kb 12.7 kb 10-14 kb   12.7-15.7 kb   8.9 kb
Symmetry of capsids Icosahedral Icosahedral Helical Helical Helical   Icosahedral    
Naked or enveloped Enveloped Enveloped Enveloped Enveloped Enveloped   Enveloped    
Baltimore class IV IV IV V V        
Virion 40-50 nm 60-70 nm 80-160 nm 80 x 7790-14,000 nm 50-300 nm 28-30 nm 40-60 nm   +
Virion polymerase + +      
Genus and species Flavivirus

Dengue viruses 1&2, YFV, JEV, WNEV, SLEV, TBEV


Hepatitis C virus





Chikungunya virus


Rubella virus




      equine arteritis virus (EAV),

porcine reproductive and respiratory syndrome virus (PRRSV)


Disease BVD caused by BVDV                
Hosts Bovine, Camelids, deer                
Clinical signs Mild fever, decreased milk production, ulcerative stomatitis, diarrhea, respiratory distress, embryonic death, abortions, birth defects,

persistently infected calves

Laboratory diagnosis Virus isolation, ELISA, VNT, IF, RT-PCR                
Target cells                  
Cellular Virus receptors                  
Viral attachment ligand                  
Virus replication Clathrin-mediated endocytosis, low pH, replicate in the cytoplasm, assemble on ER                
Reservoir host                  
Control Inactivated or attenuated vaccines are available




VEEV=Venezuelan equine encephalitis virus; EEEV=Eastern equine encephalitis virus; WEEV=Western equine encephalitis virus; BVDV=Bovine viral diarrhea virus; BD= Border disease virus; HCV=Hog cholera virus; YFV=Yellow fever virus; JEV=Japanese Encephalitis virus; WNEV=West Nile encephalitis virus; SLEV=St. Louis encephalitis virus; TBEV=Tick-borne encephalitis virus;