If you believe that you have no viruses in your body, you are wrong! The human body contains extensive colonies of microorganisms, which constitute our microbiome, and which have constantly evolved since the appearance of man. Scientists have recently begun to quantify the microbiome and have found that it is home to at least 38 trillion bacteria! However, bacteria are not the most abundant microorganisms that live in symbiosis in and on our body. This place is occupied by viruses!
The body is estimated to host over 380 trillion viruses, a community called the human virome. But these viruses are not the dangerous ones that are commonly heard of; they are not like those who cause flu or colds or dangerous infections like Ebola or Dengue fever. Many of these viruses infect bacteria that live in the body and are known as bacteriophages. The human body is a breeding ground for bacteriophages, and despite their abundance, we have very little information about what all of these or any of the other viruses in the body do.
The study of the human virome remains long behind the study of bacteria, so that only now we discover some of their most fundamental characteristics. This gap is due to the fact that it has taken scientists a long time to recognize the presence of a human virus, as well as the lack of standardized and sophisticated tools to decipher what is actually in this virome. These viruses that have evolved with us since the beginning of man are not only a part of our past, but will play a significant role in the future of human health.
Viruses are essential for the complex and dynamic network of microorganisms that are inside the body. Infections with certain viruses in the first years of life and onward have even been shown to change the expression of genes related to vaccination responses in both mice and humans, which may explain why some people are more susceptible to side effects and vaccine damage than others.
Despite the common belief that viruses are vectors of morbidity and mortality, the reality is that
about eight percent of the human genetic material comes from viruses and not from our ancestors.
Research in a 2010 study shows that the genomes of humans and other mammals contains DNA derived from the insertion of RNA viruses, whose replication and transcription takes place in the nucleus.
Most viruses are neither “good” nor “bad” because a virus could have multiple adverse but also beneficial immunomodulatory effects on the host, effects that are dependent on the anatomical location, host genotype and the presence of other infectious agents and commensal microbes. This confirms what
Louis Pasteur, the father of immunization and pasteurization, acknowledged on his deathbed: the biochemical context and the physiological environment matter, rather than the infectious pathogen.
Viruses That Keep Us Healthy?
The researchers found that the latency of some viruses can provide health benefits to the host. A 2007 study found that mice carrying latent infections with murine gamma herpes virus 68 or murine cytomegalovirus (genetic analogues to human pathogens – Epstein-Barr virus and human cytomegalovirus) were resistant to bacterial infections with Listeria monocytogenes and Yersinia pestis.
Mutations in the Hoil-1 gene cause people with risk alleles to be extremely susceptible to bacterial infections. To examine the implications of this mutation, the researchers studied mice with equivalent mutations, which died when infected with certain bacteria and parasites, including Listeria monocytogenes, Toxoplasma gondii and Citrobacter rodentium. This was due to an affected production of proinflammatory cytokines, which are necessary for resistance to these pathogens.
However, the researchers stated that latent infection with the murine herpes virus rescued mice with the HOIL-1 mutation during Listeria infection and induced high levels of the protective cytokine interferon-gamma (IFNγ). IFNγ is a cytokine that the body produces upon viral exposure, which promotes the neutralization of viruses with antibodies and the killing of viral infected cells by cytotoxic T lymphocyte immune cells and natural killer cells.
An innovative study published in Nature found that
an enteric RNA virus can replace and compensate for beneficial commensal bacteria in the gut.
The researchers found that in germ-free or antibiotic treated mice, which were infected with murine norovirus, intestinal morphology and lymphocyte function were restored, without inducing inflammation and overt disease. Norovirus “compensated” for the lack of beneficial commensal bacteria, indicating that this type of virus has the ability to support intestinal homeostasis and help restore the intestinal immunity, as does the commensal bacteria.
The conclusions of the study were that: norovirus infection triggered the repair of damaged intestinal tissue, restored many intestinal cells and intestinal cell function.
These new findings are the first strong evidence that
gastrointestinal viruses can help maintain health and heal a damaged gut.
As reported in the Science Daily article, the study’s lead investigator, Ken Cadwell, PhD, of New York University, states:
We have known for a long time that people are always infected with viruses and bacteria and do not get sick. We now have scientific evidence that not all viral infections are bad, but can actually be good for health, just as we know that many bacterial infections are good for maintaining health.
Consistent with the “hygiene hypothesis“, natural infections during and after childhood can strengthen our immune system and help balance the Th1 (innate) and Th2 (adaptive) immunity poles. Factors that disrupt this evolutionary acquired balance can contribute to an immune disorder, both by suppressing innate immune mechanisms and by over-stimulating the adaptive pole, contributing to widespread autoimmunity in the modern population.
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