What is the Difference Between Adenovirus and Retrovirus

The main difference between adenovirus and retrovirus is that adenovirus is the largest, non-enveloped virus, whereas retrovirus is an enveloped virus. Furthermore, the genome of adenovirus is double-stranded DNA, while the genome of a retrovirus is single-stranded RNA (+). Moreover, adenovirus infects both dividing and non-dividing cells, and it causes upper respiratory tract infections in both adults and children, while the retrovirus infects only dividing cells, and it has a higher tendency to cause diseases.  

Adenovirus and retrovirus are two infectious agents that come into contact with living cells to undergo replication. Moreover, they can be used as vectors to deliver desired DNA fragments to the host cell during gene therapy.  

Key Areas Covered 

1. What is Adenovirus
     – Definition, Structure, Importance
2. What is Retrovirus
     – Definition, Structure, Importance
3. What are the Similarities Between Adenovirus and Retrovirus
     – Outline of Common Features
4. What is the Difference Between Adenovirus and Retrovirus
     – Comparison of Key Differences

Key Terms 

Adenovirus, Envelope, Gene Therapy, Genome, Retrovirus, Viral Vectors

What is Adenovirus 

Adenovirus is a medium-sized DNA virus with an icosahedral protein capsid. Its genome contains double-stranded DNA. However, it does not contain an envelope, an outer lipid bilayer. Besides, it has a broad range of hosts, including vertebrates. Also, it causes a wide range of illness, including mild respiratory infections in children as well as life-threatening, multi-organ disease in people with a weakened immune system.

Figure 1: Adenovirus Structure 

Furthermore, the genome of adenovirus contains 22-40 genes. Generally, its viral particles enter into the host cell through endosomes. Also, adenovirus has high efficiency of infection. However, its DNA does not integrate into the genome of the host. Therefore, it is not suitable as a viral vector for transient expression.  

What is Retrovirus 

Retrovirus is a type of RNA virus with an icosahedral protein capsid. Its genome is single-stranded RNA (+). Therefore, with the infection, retrovirus produces DNA from its genome by using its own reverse transcriptase enzyme. Then, the resultant DNA or provirus integrates to the host genome by the integrase enzyme. Further, retrovirus contains an envelope made up of lipids and glycoprotein.

Figure 2: Retrovirus Structure

Moreover, retrovirus can serve as a viral vector, which allows the integration of foreign DNA into the genome of the host cell. Therefore, it provides a long-term stable expression. However, it only infects dividing cells. Also, its transduction efficiency is low. 

Similarities Between Adenovirus and Retrovirus 

• Adenovirus and retrovirus are two types of viruses that infect living cells. 
• They require a living cell to undergo viral replication by using cellular machinery. 
• Therefore, they are obligate parasites. 
• Furthermore, both contain a genome made up of nucleic acids and a protein capsid surrounding the genome. 
• Their protein capsid has an icosahedral shape. 
• Also, both can infect dividing cells.  
• Therefore, they cause diseases in living organisms. 
• Moreover, they serve as viral vectors to deliver desired DNA fragments to host cells. 
• Hence, they are an important tool in gene therapy. 

Difference Between Adenovirus and Retrovirus 

Definition 

Adenovirus refers to any group of DNA viruses first discovered in adenoid tissue, most of which cause respiratory diseases, while retrovirus refers to any of a group of RNA viruses, which insert a DNA copy of their genome into the host cell in order to replicate. Thus, this is the main difference between adenovirus and retrovirus.

Genome 

Adenovirus contains double-stranded DNA in the genome, while retrovirus contains single-stranded RNA (+) in the genome. Hence this is also an important difference between adenovirus and retrovirus.

Envelope 

Another difference between adenovirus and retrovirus is that the adenovirus is a naked virus without an envelope while retrovirus contains an envelope. 

Virion Diameter 

The diameter of adenovirus is 70-90 mm while the diameter of a retrovirus is 80-130 mm. 

Genome Size 

The size of the adenoviral genome is 39-38 kb while the size of the retroviral genome is 3-9 kb. 

Virion Polymerase 

Moreover, adenovirus contains negative virion poymerase while retrovirus contains positive virion polymerase. 

Tropism 

Also, tropism is another difference between adenovirus and retrovirus. Adenovirus infects both dividing and non-dividing cells while retrovirus infects only dividing cells. 

Host Genome Interaction 

Adenovirus is non-integrating while retrovirus is integrating. 

Transgene Expression 

Transgene expression in adenovirus is transient, while the transgene expression in retrovirus is long-lasting. 

Packaging Capacity 

Furthermore, the packaging capacity of adenovirus is 7.5 kb, while the packaging capacity of a retrovirus is 8 kb. 

Advantages in Gene Therapy 

Besides, adenovirus has a high and broad transduction efficiency, and it can grow to high titer, while retrovirus has persistence gene transfer, and it is useful for cell marking and lineage analysis. 

Disadvantages in Gene Therapy 

Occasional cytotoxicity and the possibility of a strong immune response are the disadvantages of adenovirus while insertional mutagenesis is a disadvantage in retrovirus. 

Conclusion 

Adenovirus is the largest type of non-enveloped virus, containing a double-stranded DNA. Also, as it contains DNA, its virion polymerase is in the negative form. However, it has a strong tropism for most tissues. As a viral vector, its genetic material is episomal; hence, it is transient. On the other hand, the retrovirus is an RNA virus with an envelope. Also, it contains single-stranded RNA (+). Therefore, it has a positive RNA polymerase. However, it infects only dividing cells. Moreover, its genome integrates into the host genome. Hence, its gene transfer is persistence. Thus, the main difference between adenovirus and retrovirus is the structure and features of gene transfer.

References:

1. “Viral Vectors.” Gene Therapy Viral Vectors Explained, Gene Therapy Net. , Available Here.

Image Courtesy:

1. “Adenovirus 3D schematic” By Thomas Splettstoesser (www.scistyle.com) – Own work (CC BY-SA 4.0) via Commons Wikimedia   
2. “Retrovirus” By Thomas Splettstoesser (CC BY-SA 4.0) via Commons Wikimedia