Why are viruses referred to as being obligate parasites?
Question: Why are viruses referred to as being obligate parasites?
Viruses are referred to as being obligate parasites because they are completely dependent on host cells to replicate and survive. Unlike other microorganisms such as bacteria, viruses are not considered living organisms because they cannot carry out metabolic processes on their own .
In this blog post, we will explore the characteristics of viruses and why they need host cells to function. We will also look at some examples of viruses that cause human and animal diseases.
What are viruses?
Viruses are acellular entities that consist of a protein coat called a capsid and a genetic material that can be either DNA or RNA. Some viruses also have a lipid envelope that surrounds the capsid. Viruses are very small, ranging from 20 to 300 nanometers in size.
Viruses do not have any cell organelles such as ribosomes, mitochondria, or Golgi apparatus. They also lack the enzymes and machinery needed to synthesize proteins or generate energy. Therefore, they cannot grow, divide, or reproduce by themselves. They need to infect a living cell and use its resources to make copies of themselves .
How do viruses infect host cells?
Viruses can infect different types of cells, such as bacteria, plants, animals, or humans. They can also be specific to certain tissues or organs within a host organism. For example, HIV infects only certain types of white blood cells, while influenza infects mainly respiratory cells.
To infect a host cell, a virus must first attach to a specific receptor on the cell surface. This is determined by the shape and structure of the viral capsid or envelope. Then, the virus must enter the cell either by fusing with the cell membrane or by being engulfed by the cell through endocytosis.
Once inside the cell, the virus releases its genetic material and takes over the cell's machinery. Depending on the type of virus, it can either integrate its DNA into the host cell's genome or use its RNA as a template to make more viral RNA. The virus then uses the host cell's ribosomes and amino acids to make viral proteins. These proteins are assembled with the viral genetic material to form new virus particles. The new virus particles then exit the cell either by budding off the cell membrane or by causing the cell to burst (lyse). The released virus particles can then infect more cells and repeat the cycle .
What are some examples of viral diseases?
Viruses are responsible for many diseases that affect humans and animals. Some of these diseases are:
- HIV/AIDS: This is caused by the human immunodeficiency virus (HIV) that infects and destroys certain types of white blood cells called CD4+ T cells. These cells are essential for the immune system to fight off infections and cancers. As a result, people with HIV/AIDS become vulnerable to opportunistic infections and malignancies that can be fatal.
- Influenza: This is caused by various strains of influenza viruses that infect mainly respiratory cells. The symptoms include fever, cough, sore throat, muscle ache, and fatigue. Influenza can cause complications such as pneumonia, bronchitis, or ear infections. In some cases, it can also lead to death, especially in young children, elderly people, or people with chronic conditions.
- COVID-19: This is caused by a novel coronavirus (SARS-CoV-2) that emerged in late 2019 in China and spread worldwide in 2020. The symptoms include fever, cough, shortness of breath, loss of taste or smell, and fatigue. COVID-19 can cause severe respiratory distress syndrome (ARDS), organ failure, blood clots, or death in some cases.
Conclusion
Viruses are referred to as being obligate parasites because they cannot survive or reproduce without host cells. They hijack the host cell's machinery to make copies of themselves and cause various diseases in humans and animals.
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