Viruses: Friend or Foe?

Beyond the Bad Rap: How Viruses Can Be Our Unsung Heroes

When you hear the word “virus,” what comes to mind? Perhaps the common cold, a cold sore, or even a global pandemic like the one caused by the coronavirus that may have originated in bats. While viruses are undeniably known for causing diseases, recent discoveries and ongoing research are unveiling their crucial and often beneficial contributions to life on Earth. In fact, these microscopic entities, which are often considered neither dead nor alive, play pivotal roles in ecosystems and hold immense potential for human health and environmental sustainability.

What Exactly is a Virus?

Viruses are fascinating infectious units that are incredibly small, ranging from about 16 nm to over 300 nm in diameter, making them ultrafilterable (not retained by bacteria-proof filters). They are essentially composed of proteins and contain only one type of nucleic acid—either DNA or RNA. A virus’s genetic material is enclosed within a protein shell called a capsid. Some viruses also possess an outer lipid membrane, referred to as an envelope, which contains material from both the host cell and the virus itself.

What makes viruses unique is their mode of reproduction: they do not reproduce by division like other cells. Instead, they are intracellular parasites, meaning they are obliged to depend on a host cell for replication. They lack their own protein synthesis machinery (ribosomes) and energy-generating metabolic pathways, so they must hijack the host cell’s mechanisms to produce their components and replicate their genomes.

The Order in the Viral World: Classification

To manage the vast diversity of viruses, scientists rely on structured classification systems. The International Committee on Taxonomy of Viruses (ICTV) is the global authority that scrutinizes, approves, and ratifies taxonomic proposals, maintaining a comprehensive list of virus taxa. The ICTV mandates that virus species names be written in a binomial format (genus + species epithet), similar to how living organisms are named.

Another important system is the Baltimore Classification, which groups viruses into seven classes based on their genetic material (DNA or RNA, single-stranded or double-stranded) and how they produce messenger RNA (mRNA). This classification scheme helps virologists understand viral replication strategies and evolutionary relationships.

Viruses as Unexpected Allies: The “Good” They Do

While viruses are often associated with disease, they have a surprisingly diverse array of beneficial applications and natural roles:

• Biocontrol Agents for Pest Management Viruses are being increasingly used as biopesticides, offering environmentally friendly alternatives to synthetic chemical pesticides.

  • Granuloviruses are naturally occurring viruses that can infect and kill the larval stages of specific insect pests, primarily those in the Lepidoptera order, like moths. These viruses are highly host-specific, meaning they target only certain pests and typically cause no harm to beneficial insects, humans, or wildlife. An example is the Cydia pomonella granulovirus (CpGV), which targets the Codling moth and is used in products like Madex HP®. The pest must ingest the virus, for instance, by eating leaves treated with a granulovirus-based biopesticide.
  • Nucleopolyhedrovirus (NPV) is another type of virus that offers a sustainable and environmentally friendly approach to controlling caterpillar populations, helping farmers maintain healthier crops while preserving biodiversity. Research is also exploring Nucleopolyhedrovirus Coocclusion Technology as a new concept in developing biological insecticides.
  • Viruses are also employed in large-scale population control, such as in Australia, where the Myxoma virus (since 1950) and the Rabbit Haemorrhagic Disease Virus (RHDV) (since 1995-96) have been successfully used to reduce wild rabbit populations. More recently, a new virulent strain, RHDV2, emerged in Australia in 2014 and has the unique ability to overcome immunity to other strains and infect rabbits of any age, contributing to a sustained reduction in rabbit populations.
  • The U.S. Environmental Protection Agency (EPA) plays a role in regulating biotechnology for use in pest management, including biopesticides.

• Phage Therapy: Battling Bacterial Infections Bacteriophages, or “phages,” are viruses that specifically target and infect bacteria. They utilize the host bacterium’s replication mechanisms to produce new virions, which then lyse and kill the bacterial cell.

  • Phage therapy has re-emerged as a promising alternative to antibiotics, particularly in the face of rising multi-drug resistant bacterial infections. Clinicians have used phages to treat bacterial infections since the early 20th century.
  • Phages are incredibly abundant in the human gut and play a crucial role in shaping the bacterial composition and diversity of the gut microbiota. They act as natural predators, selectively infecting and killing specific bacterial strains, thereby helping to maintain gut balance.
  • Their interactions with host bacterial strains also contribute to modulating the immune system and play a role in human metabolic processes and overall well-being.
  • Phages have shown promise in treatments like Fecal Microbiota Transplantation (FMT) for Clostridioides difficile infection, helping to reconstruct a healthy gut environment. Studies have also indicated that Fecal Virome Transplantation (FVT) could mitigate weight gain and glycemic abnormalities in murine models of type 2 diabetes and obesity.
  • While promising, research continues to explore the complex interactions of phages with bacteria and the immune system, addressing challenges such as the potential for phages to evolve or transfer genetic material.

• Oncolytic Viruses: Fighting Cancer Oncolytic viruses (OVs) are a field of cancer therapy that involves viruses that can preferentially infect and kill cancer cells. This area of research is actively being explored for its potential to treat various cancers, including through genetic engineering of these viruses.

• Other Surprising Benefits

  • Our own genetic makeup reveals the deep integration of viruses: over 40% of mammalian genomes comprise sequences derived from endogenous retroviruses (ERVs). These inherited genetic elements, resembling proviruses from past infections, have been harnessed by hosts for beneficial functions, such as their role in placental development, and their regulatory potential has been exploited to regulate genes and gene networks during evolution.
  • Viruses may even aid in the recovery of endangered species. For example, viruses may help the American Chestnut, once a vital forest tree, recover from the Chestnut Blight that nearly wiped it out in the early 20th century.
  • Some giant viruses have been discovered to carry genes for metabolic pathways (like rhodopsin-like proteins for photoheterotrophy in a choanoflagellate virus), suggesting mutualistic relationships where the virus provides a new metabolic pathway for its host.

In conclusion, while viruses often carry a reputation for disease, their intricate roles in nature extend far beyond pathogenicity. From serving as targeted biocontrol agents and potent tools against antibiotic-resistant bacteria to offering novel avenues for cancer treatment and even shaping the evolution of host genomes, the “good” that viruses do is truly remarkable and continues to be a frontier of scientific discovery.