What is the Difference Between Alphavirus (Togavirus) and Flavivirus

The main difference between Alphavirus (Togavirus) and Flavivirus is that Alphavirus contains structural proteins at the 5′ end, whereas Flavivirus contains structural proteins at the 3′ end.

Alphavirus and Flavivirus are two viruses with a positive-strand RNA genome. They contain a non-segmented genome, approximately 11 kb in size.   

Key Areas Covered

1. What is Alphavirus (Togavirus)
– Definition, Features, Importance
2. What is Flavivirus
– Definition, Features, Importance
3. Similarities Between Alphavirus and Flavivirus
– Outline of Common Features
4. Difference Between Alphavirus (Togavirus) and Flavivirus
– Comparison of Key Differences

Key Terms 

Alphavirus, Togavirus, Flavivirus

What is Alphavirus (Togavirus)

Alphavirus is a disease-causing virus that occurs in two forms. Eastern, Western, or Venezuelan equine encephalitis viruses like virus produce one form that shows symptoms such as fever, malaise, headache, and symptoms of encephalitis. The other form contains chikungunya, Ross River, Mayaro, and Sindbis viruses, causing fever, rash, and arthralgia. Also, Alphavirus is an enveloped virion that is spherical. Its diameter is 60-70 nm. The lipid-containing envelope of the Alphavirus contains glycoproteins for the mediate attachment, fusion, and penetration.

Figure 1: Alphavirus

Furthermore, Alphavirus is one of the two genera of the family Togaviridae. The other genus is Rubivirus (rubella virus). There are 27 Alphaviruses classified according to their antigenic properties. Importantly, the Alphavirus infection transmits via infected mosquitoes. 

What is Flavivirus

Flavivirus is also a disease-causing virus that causes encephalitis. The viruses that cause encephalitis include St.Louis, Japanese, Powassan, and tick-borne encephalitis. Also, it can cause febrile illness with rash by dengue virus. Other forms of Flavivirus include Kyasanur Forest disease virus and sometimes dengue virus, which causes hemorrhagic fever, and yellow fever virus, which causes hemorrhagic fever with hepatitis. However, the spherical virion of the Flavivirus is 40-50 nm in size.

Figure 2: Flavivirus

Moreover, one surface glycoprotein on the envelope is responsible for mediating the virion’s attachment, fusion, and penetration during infection. The initiation of the infection occurs through the mosquito or tick bite. 

Similarities Between Alphavirus and Flavivirus

• Alphavirus and Flavivirus are two RNA viruses that contain a positive-stranded RNA genome.
• Their genome is non-segmented.
• The size of the genome is around 11 kb.
• They transmit through arthropod vectors. 

Difference Between Alphavirus (Togavirus) and Flavivirus

Definition

Alphavirus refers to a genus of single-stranded RNA viruses of the family Togaviridae that are transmitted by arthropods and especially mosquitoes. In contrast, Flavivirus refers to any group of RNA viruses, mostly having arthropod vectors, which cause several serious human diseases. 

Structural Genes in the Genome

Alphavirus contains structural proteins at the 5′ end, while Flavivirus contains structural proteins at the 3′ end.

Sub-Genomic Message

Alphavirus produces sub-genomic messages, while Flavivirus does not.

Polyadenylation

Alphavirus does not contain polyadenylation at the 3′ end, while Flavivirus contains polyadenylation at the 3′ end. 

Examples

Examples of Alphavirus are eastern, western, or Venezuelan equine encephalitis viruses, chikungunya, Ross River, Mayaro, and Sindbis viruses, while examples of Flavivirus are St.Louis encephalitis, Japanese encephalitis, Powassan, tick-borne encephalitis viruses, dengue virus, and yellow fever virus. 

Symptoms

Alphavirus causes fever, malaise, headache, and symptoms of encephalitis, rash, and arthralgia, while Flavivirus causes encephalitis, febrile illness with rash, and hemorrhagic fever with hepatitis.

Conclusion

In brief, Alphavirus and Flavivirus are two genera of viruses that contain positive-sense RNA genomes. Their genome is around 11 kb. The structural proteins of the Alphavirus occur at the 5′ end of the genome. It produces subgenomic messages. Also, it does not contain polyadenylation at the 3′ end. Alphaviruses include eastern, western, or Venezuelan equine encephalitis, chikungunya, Ross River, Mayaro, and Sindbis. The symptoms of the diseases of Alphavirus include fever, malaise, headache, and symptoms of encephalitis, rash, and arthralgia. In comparison, Flavivirus contains structural genes at the 3′ end. However, it contains polyadenylation at the 3′ end. St.Louis encephalitis, Japanese encephalitis, Powassan, tick-borne encephalitis viruses, dengue virus, and yellow fever virus are examples of the Flavivirus. Encephalitis, febrile illness with rash, and hemorrhagic fever with hepatitis are the symptoms of Flavivirus. Therefore, the main difference between Alphavirus and Flavivirus is their genome.

References:

1. Schmaljohn AL, McClain D. Alphaviruses (Togaviridae) and Flaviviruses (Flaviviridae) In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 54.

Image Courtesy:

1. “Ijms-20-04657-g003” By Madiiha Bibi Mandary, Malihe Masomian, and Chit Laa Pooh – Own work (CC-BY 4.0) via Commons Wikimedia
2. “Viruses-10-00597-g001 ” By Ginés Ávila-Pérez, Aitor Nogales, Verónica Martín, Fernando Almazán, and Luis Martínez-Sobrido – Own Work (CC-BY 4.0) via Commons Wikimedia