Are Viruses Alive: Viruses, Viroids, and Prions

According to Villarreal in his article “Are Viruses Alive,” notes that biologists have suggest that viruses, viroids, and prions are in a gray area between living and non-living organisms; they portray some characteristics that qualify them to be living organisms; however some of their characteristics hinder their full qualification (Villarreal, 2004). This paper will discuss whether viruses, viroids, and prions qualify to be living organisms.

Characteristics of living things

Although there are some difficulties defining what life is, living organisms that are not in non-living organisms share some characteristics; for instance living organisms have complex series of organic movements. On the other hand, organs result from cells, which form tissues that accomplish a certain shared function. Living things have a metabolism, an exchange of chemical matters with the external environment; it is through metabolism that living things release and get chemical energy. Through sexual or asexual processes, living things reproduce; during this processes, the parent organism has genetic contribution to the new organism. With time, living organisms grow and undergo evolution to be able to metabolize, respond, and reproduce; this is different from non-living organisms; they also have the potential to hibernate in different environments (Dennis, Gray, Kauffman, McNair and Woolf, 2009).

Structure and characteristics of Viruses, Viroids and Prions

Viruses, viroids, and prions are different in their own merit however they share some common characteristics; they are acellular particles that behave more the same like livings however they lack some basic characteristics to fully qualify as living organisms. The structure of the organisms leads to their common characteristics which include; they are not made of cells that define the nature and characteristics of living organisms. Viruses, viroids, and prions can neither reproduce on their own nor transform to energy; this characteristic of not transforming to energy denies them the machinery for protein synthesis. Despite the similarity in structure that makes viruses, viroids, and prions share some characteristics, they are different in their nature, form, and operations.

Viruses are disease causing organisms that consists of proteins, nucleic acid (genetic material), and sometimes lipids, they exists in the form of intracellular and extracellular viral.

Prions take the form of proteins but have the potential of taking abnormal forms to cause disease called transmissible spongiform encephalopathies; once in a cell, they are able to convert other proteins to a form that is harmful to the cell they are attached.

Viroids are disease causing organisms that have the main characteristic of absence of a capsid; they are the smallest know disease causing organisms that infect plants (Amor and Surekha, 1993).

Diseases caused by Viruses, Viroids, and Prions

Viruses cause different diseases in animals, humans, and plants; the disease and its symptoms depends on the viral species; some of the most common human viral diseases are cold sores, flu, common cold, Aids, Eboka and chickenpox. Viroids causes’ disease in plants and animals, some of the most common disease are Potato spindle tuber, Tomato plant macho, and Hepatitis D. Prions caused disease are common in animals; some of the common know diseases caused by prions are Creutzfeldt-Jakob disease, Mad Cow Disease, and Scrapie.

Types of viruses

The symptoms and the type of diseases that virus cause lead to their classifications; when using their structure , they can be classified into three as Helica, which is a single capsomer, around a protein, cosahedra which is a three dimensional geometric with 20 sides, and the third type is complex virus shell which changes its structure with environment (Amor and Surekha, 1993).

Definition of life

Although there is no universally accepted definition of what is life, there are some characteristics that biologists have brought forward to define life; some of the characteristics of life advocated by biologists include the ability to have self organization, ability to move/develop/grow, ability to adopt, reproduce and have energy conversion.

Own opinion on whether Viruses, Viroids, and Prions are living

In my own opinion viruses, viroids, and prions do not merit being living organisms; the main reason behind the standpoint is that they require a living host to reproduce. Secondly, when viruses, viroid, and prions are studied independent of a cell, they lack living organisms’ characteristics like energy conversion, adoption, and Responsiveness.


Amor, S. and Surekha, M. ,1993. Prions, viruses, and antiviral drugs. Lancet, 342(8870), p. 545.

Dennis, L., Gray, R., Kauffman, L., McNair, J. and Woolf, N.,2009. A Framework Linking Non-Living and Living Systems: Classification of Persistence, Survival and Evolution Transitions. Foundations of Science, 14(3), pp. 217-238.

Villarreal, L., 2004. Are Viruses Alive? Scientific American, 291(6), pp. 100-105.