The Emerging Concept of “Giant” Virus, Assessment Example

Press Release

Our recent virology studies have led to the discovery of a new virus known as Acanthamoeba polyphaga mimivirus. The virus exhibits different characteristics from normal virus, including a large size and complex genome, leading us to classify it as a giant virus.  The traditional perspective of the virus has always been that they are submicroscopic in size. Viruses are also characterized by the minimal genome complexity since they only pack genes responsible for their replication mechanism inside a host. Such limited perception of viruses has deterred the discovery of giant protozoan virus. Previous studies on intracellular microbes in amoeba, for instance, shows that the pandoraviruses were initially treated at parasite of amoeba. Similarly, the discovery of Acanthamoeba polyphaga was also met with certain speculations. It’s complex structure and size had initially led to the thought that the organism was an intracellular bacteria of amoebae. However, further analysis revealed the lack of ribosomal DNA in the organism.

Mimivirus’ discovery has challenged many aspects that are associated with normal viruses. The virus, for instance, is large than the previously largest virus and possess particle size up to 750nm. Their size makes it easy to observe them under a light microscope, unlike other viruses that require advanced microscope. Particle size is an important factor in isolation protocols. Filters with pores size of 0.2-0-3um are often preferred considering the small size of viruses compared to cellular organisms. The size of mimivirus is within the nanometer range making conventional filters ineffective in isolation procedure.

Our database on the viral genome also shows that the largest genome size to be the bacillus phage G at 497.5kb. The mimivirus, in contrast, has a genomic size of 1181.4 kb. It genome length exceeds 1.2 million base pairs – a feature commonly associated with cellular organism. It is postulated that giant viruses such as mimivirus have been prevalent in the environment. The viral population in the natural environment exceeds that of cellular organisms to a great extent. A large proportion of DNA sequences collected from the environmental surface has often led to ambiguous results regarding the origin of the genetic material. It is often thought that bacteria may be the source of the genetic material. However, an analysis of the genetic information of mimivirus reveals that 15% of the gene sequences resembled that of previously collected environmental DNA samples. It is, therefore, likely that our limited perspective on the size of the viral genome has prevented earlier discovery of the virus in nature.

A further analysis of the genetic information reveals that they have a large gene repertoire consisting of 911 protein codon genes. This is unusual for a virus considering that most viral genome have a small gene repertoire that encodes for genome packaging proteins, the capsid, and proteins essential for infecting the host cells. mRNA and more than 200 proteins have been discovered in these giant viruses, which is evidence of their broad gene repertoire. A lot of proteins unrelated to DNA replication have also been found in the giant virus. It should also be noted that mimivirus is susceptible to infections by virophages – such infection trigger defense mechanism through the mimivirus virophage resistant element. The complexity of the new virus overlaps with what is found in the smallest bacteria and eukaryotic organisms, making this an interesting subject for further research.

Fact Sheet

Acanthamoeba polyphaga mimivirus

Acanthamoeba polyphaga mimivirus (AMPV) is a giant virus that causes viral pneumonia infections in humans.

Virology

Acanthamoeba polyphaga mimivirus is a DNA virus belonging to the Mimivirus genus class of the Mimiviridae family. The virus exhibits high specificity for amoeba host. However, it can also infect humans.

Clinical Signs

Mimivirus infection in humans can result in the development of viral pneumonia and other respiratory disorders. Infected patients should lookout for the following symptoms:

• Unexplained respiratory infection
• Greenish, yellow or bloody mucus from coughs
• Chest pains during deep inhalation
• Shortness of breath
• Low-grade fever and chills
• Loss of appetite
• Fatigue and low energy
• No recovery with one week of administration of antibiotics

Epidemiology of Transmission

The first case of acute pneumonia associated with AMPV was first observed in 1992 in Bradford, England. It was initially thought to be a bacterium but later identified correctly as mimivirus in 2003. Different cases have been identified all over the world ever since with the virus indicating its presence globally.

AMPV is present in soil and water. It can survive in diverse climatic conditions. It is transmitted by contact with contaminated surfaces and the consumption of water contaminated water. The virus infects amoeba at the trophozoite stage. Consumption of water contaminated with infected amoeba leads to the release of the virus into to body. The virus can also enter the body. AMPV, like other pneumonia-causing viruses, attacks the respiratory tissues. It is effects people with compromised immunity, such as the elderly. Mimivirus is extremely resistant to degradation by physical and chemical agents. It is also protected by amoeba.

Treatment and Control

Treatment entails the use of antiviral drugs. Close monitoring is essential to prevent recurrence. Maintaining high standards of hygiene and drink purified water controls the spread of the disease. Practicing frequent handwashing, especially after handling soils, prevents the spread of the bacteria.

References

Claverie J, Ogata H, Audic S, Abergel C, Suhre K, Fournier P. 2006. Mimivirus and the emerging concept of “giant” virus. Virus Research 117:133-144. [accessed 2020 May 9]