Viruses: An Introduction

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In this article, we discuss the basics of viruses, how they can harm or benefit human health, and basics of testing.

How viruses cause disease:

  • Out of millions of viruses, 320,000 (Anthony SJ, 2013) different viruses can infect mammals, out of which only 219 (Woolhouse M, 2012) are currently known to infect humans.
  • A virus can only survive when incorporated into a host organism. They do not have the biological machinery needed to survive and replicate, so rely on their host’s cellular mechanisms for survival and reproduction.
  • Once a virus reproduces inside a cell, the new virions (individual viral particles) break out of the cell to move into the bloodstream and infect new cells. Breaking out of the cell causes lysis (cell death), which is one of the primary mechanisms through which viruses cause disease – when enough cells die, a disease process can manifest.
  • Viruses can also cause disease through the stimulation of an excessive or misdirected immune response, leading to tissue damage

How viruses can benefit human health:

  • Humans have co-evolved with viruses over millions of years and viral DNA, particularly endogenous retroviral (ERV) DNA, makes up a significant portion of human DNA (Grandi N, 2018).
  • Not only do most viruses not cause significant disease but can also be beneficial through evolutionarily adaptive DNA integration, immune system entrainment, and by existing as an essential component of our microbiome (called the virome).
  • Integration of specific retroviral DNA into human DNA has also been demonstrated to increase immune function (NIH, 2016).
  • The human virome is the sum-total of all viruses on and in our body. There are an estimated ten times more bacterial cells than human cells constituting a human body and likely many times more virions than bacterial cells comprising our microbiome.
  • The primary type of virus in our gut microbiome are called bacteriophages, which are viruses that infect bacteria. These can help balance the microbiome.

Testing for viruses:

  • Testing for viruses falls under two broad categories: directly testing for the presence of the virus or testing the immune system to infer either a current or past infection.
  • An important concept to note when testing for viral infections is ‘sensitivity and specificity’.
  • Types of testing for viruses include:
    • PCR
    • Antibody testing
    • ELISA
    • Nagalase

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