Ode to Viruses

I am writing an ode to viruses because they meritoriously deserve one.  Also, because I want to highlight how we as creatures of habit, cannot refrain from negatively stereotyping things. For instance, just a year ago, I observed the impact of consumer bias against a beverage named ‘Corona’; just because the beverage’s name was horrifically synonymous with the prevalent virus pandemic. People blacklisting anything mildly symmetrical to corona, due to the fear of corona viruses was shocking. Thirdly, I applaud viruses because my Virology Professor graded my paper as a B, keeping me from scoring a distinction and immensely humbling me in the process; so now I seek goodness even in nooks and crannies.

When Viral ecologist Marilyn J. Roossinck from Penn State University was asked about “What would a virus free world look like?” She said, “There wouldn’t be a world. I think that viruses are probably remnants of the original life form. It’s high time they get their due credit.” Viruses are the most abundant entity found everywhere on planet earth. We are familiar with only a small fraction of the existing viruses and this knowledge is expanding with the discovery of new virus-like genetic sequences. Viruses can be classified based on their shape (helical, spherical, and polyhedral), their choice of host (animals, plants, bacteria) or the type of genetic material (DNA or RNA) they carry. In Greek phagein means to devour, hence the term phage is used particularly for the viruses that infect bacteria. Viruses can be characterized as i) Parasitic viruses (virus harms host) e.g tomato bushy stunt virus that deforms eggplant. ii) Commensals (no effect on host) e.g., viruses infecting humans causing no problem to host. iii) Mutualistic (virus helps host) e.g bacteriophages that help cholera virus to make necessary toxins.  iv) Symbiogenetic (viral genes help host) e.g., viral genetic material that allows formation of placenta in mammals.

Viruses need hosts to replicate

Viruses cannot replicate without host cells. They are known to adeptly invade human tissues in mouth, gut, respiratory tract, blood and urine; surprisingly some bystander viruses are recently found in organs which are considered sterile such as cerebrospinal fluid, blood plasma, joint fluids, breast milk. Previously only rare viruses (such as herpes virus) were known to invade cerebrospinal fluid but recent researchers are establishing central nervous system colonization by a diverse viral community.

Viruses and human hosts

Viruses inhabit every corner of the human body. From head to toe in human anatomy they have been located in the nervous system, mouth,respiratory tract, mammary glands, gastrointestinal tract, urinary tract, genitals, and in joint fluids, blood and skin surface. Among 100 known Herpes virus specie, only nine infect humans, mainly Herpes simplex type1 (causing cold sores), Herpes simplex type 2 (genital herpes), Varicella zoster (chickenpox, shingles), Epstein- Barr (lupus, cancer), Cytomegalovirus (pneumoniae).

The u in humans is followed by v in viruses

Scientists are emphasizing how the human body is a medium of coexisting cells, bacteria, fungi and most abundantly viruses. We are not just human cells, in entirety; and  the human microflora is not just a percentage of biological matter in the human body. The estimated 380 trillion viruses living inside the human body is 10 times the number of bacteria.  Hence the virome of the human body which is being mapped for a decade; is somewhat like a partnership that influences human function in both good and bad ways. The challenge is on us to tap into the good aspect of the viruses and viral determinants residing in the human body.

The story of virome begins...

The presence of viruses in any infant gut indicates their earliest acquisition from the mother's body i.e birth canal, later from breast milk and years on a virome keeps building from the surrounding air, water, food and humans. Interestingly adult viromes are very stable, as anello viruses are very common among the human population. When we talk about the active and changing microbiome in humans, the most dynamic players indeed are viruses! The virome of the human body differs in different organs. The viruses in the stomach are different from those of the mouth. Researchers can now tell which part of the body is under scrutiny by looking at its virome profile. As a naturally occuring entity in the environment, viruses are routinely picked up by individuals from their surroundings. Hence people living together tend to share 25% of the viruses in their virome which might be exchanged or transmitted by casual contact, utensils, food, furniture and toilets. Viromes of people can vary based on gender and population distribution. Oral viromes of men and women vary, and people in Western nations have less diverse viromes as compared to people in the other side of the world.

Viruses living upon bacteria inside humans; “Phages”

The viruses inside human body target bacterial and human cells alike. Those living inside bacterial cells within the human body are called bacteriophages or simply phages. They are present everywhere, in the air, the human body, and even in acid mines, hot springs and arctic glaciers. Phages are known to cross mucosal membranes of intestine, lungs, liver, kidney but perish upon crossing into the nervous system where no host bacteria are available.

You have got crAssphage so do I!

crAssphage has a universal prevalence, though found in the human population worldwide, it is not linked to any disease and researchers are rather uncertain about its influence on the human hosts. Since it can control the bacterial population of bacteroides in the human gut, it can be exploited for improving gastrointestinal conditions in humans.

What keeps viruses at bay

A very small fraction of viruses in our virome can infect human cells; but under normal conditions those viruses are kept in check hence, at bay and suppressed by our immune system. In case our immunity gets compromised; then eradication of pathogenic viruses becomes a challenge.

Benevolence of Viruses

·        Viruses can protect against human pathogens

An example of viruses protecting against human pathogens is that of GB virusC, a common bloodborne human virus  that is an antagonist to the HIV virus and fatal Ebola virus. GB virus C slows the progression of AIDS upon HIV infection.

·        VDEPT;

Viruses used as enzyme factories for virus directed enzyme prodrug therapy (VDEPT). In cures for cancers where a drug is required to target specific human tissues and not others; the inactive prodrug is systemically administered along with virus encoding enzyme within the targeted tissues. An example is the administration of ganciclovir along with thymidine kinase expressing adenovirus; in the treatment of HIV infection.

·        Phage therapy

Phages previously isolated from local water bodies, dirt, air, sewage and patient body fluids were purified and used for treatment of dysentry, sepsis and skin infections. In current times phages are genetically engineered against target bacteria (those resistant to antibiotics) and can be stored individually as purified strains or as bacteriophage stocks (cocktail mixture of different viral strains). Rockefeller University researchers are using phage enzymes to fight MRSA infections (methicillin resistant Staphylococcus). Similarly, in 2016 at U.C San Diego doctors used phages to treat the multiorgan failure condition of a patient due to drug resistant bacteria (Acinetobacter). Phage therapy has its limitations since effective viruses are hard to find; even if phages are lab grown and cultured in bacteria; the purification of phages from bacteria requires sophisticated methods.

·        Viruses as de facto immune systems; by trapping bacteria.  

How exactly viruses act as a de facto immune system has not yet been proven but researchers in Finland have established a strong association of viruses present in mucus with eradication of a particular bacterium only in pigs and rainbow trout.

·        Viruses are the major recyclers in the oceanic environments

They are also known to kill the winner thus maintaining a balance in the ecosystem. They can also act as symbionts for fungi that allow grass to grow upon desert soils.

Viruses have gained fair share of notoriety over the years, starting from the 1918 influenza epidemic costing 50 to 100 million lives, followed by 20th century smallpox invasion with approximately 200 million deaths and most recently 21st century Covid-19 pandemic is just another blow in the series of unfortunate events. However, wishing for a virus free world would be a mistake with repercussions deadlier than a deadly virus. As Tony Goldberg said “All the essential things they do in the world far outweigh the bad things”. Viruses may appear as a mystery to us but they are an integral truth. And we need to make peace with the fact that they are keeping us alive and sustaining the planet rather than killing us!