It may seem strange enough that cell-wise, we're more bacterial than human. We have more bacterial cells than human cells in each of us. Bacterial cells outnumber human cells 10:1. That it so say, bacteria out number us, our human cells, 100 trillion to 10 trillion.

Thing is, there are more viruses than bacteria in us. It is thought there are 10 times as many viruses as there are bacterial cells. This means we have 100 viruses for every human cell.

They're just not all in the human cells - they may be in the bacteria in us - or the other fungi and parasites. They are also - of course - incredibly small. By weight, we're only 1-3% bacteria - so it's likely just about 3 pounds. Viruses are a lot, lot smaller - large in number, but not noticeable in weight.

This isn't a surprise.

Viruses appear to be the most common biologic entity on our planet. In one milliliter of sea water, there are 10,000,000 virus particles. It is thought that all the different viruses in the world collectively number up to 10 to the 31st power. That's 1 followed by 31 zeroes. In other words, that's a lot of viruses.

Just as bacteria in our bodies collectively make up our human microbiome; viruses collectively make up our human virome.  Some of these viruses may have no effect; some may affect the bacteria in us. Some may be latent - asleep - and the suddenly awake - maybe in times of stress or when our immune system defense is weak - and then cause us harm.

Other viruses may help us. It's a pretty big knot for us to untangle.

We don't fully know what this means for our health. 

What we do know:

Our human virome is constantly changing. The collective virome contains "fastest mutating genetic elements on Earth". The virome inside of us is changing and mutating faster than our genome (our human genes) and the microbiome (all the bacteria in us).

The human virome contains a lot more than the viruses that make us sick. These include viruses that infect our cells, that infect the bacteria and other organisms (fungi, parasites) in us, and parts of our own chromosomes that our virus-derived. Some of these viruses can be beneficial.

Viruses can help us. Some viruses in our saliva can help 'weed out' dangerous bacteriaViruses can help keep our guts safe - in the face of pathogens and antibiotics that wipe out friendly bacteria.

There are bacteriophages - viruses that infect bacteriaThese bacterial viruses may enter bacteria and if they are lytic bacteriophages, they may cause the bacteria to breakdown. This may help control certain bacteria populations and is considered a possible treatment for antibiotic resistant bacteria.

It's hard to study our virome. These viruses are very hard to detect and sequence because they are contained within so many different types of cells in our bodies. The virome constantly changes and does not have a conserved set of genes that quick sequencing methods can easily detect.


As we learn more about the virome, we learn more about our genome. We will start to understand the 'fossils' of old viruses in our DNA and understand how these can even regulate our own genes.

We have many known persistent or latent infections. There are likely many more that we do not know about - haven't even identified - which may affect us in ways we haven't imagined. 

We do, however, know that many carry known viruses they don't know they carry. These viruses are often latent - sleeping - and can awaken to affect our health.

In fact 35 million are living with HIV and around 39 million have died. This is a virus that can quietly be inside a person for 10-15 years without causing disease until later leading to AIDS.

Most have had Varicella (VZV) - after an infection with chickenpox. After initial infection can awaken and cause zoster.

Most have herpes, though may not know it, as outbreaks aren't always apparent. This virus can cause occasional flairs but can also rarely lead to more serious problems like encephalitis, swelling of the brain.

Many have HPV, which can cause no problems, but for some this can lead to cervical, throat, anal, or penile cancer.

​There is also CMV, which is carried by most people, and which can reactivate in times of stress (such as during illness) and cause further illness. This virus can also lead to transmission to a baby peri-partum (either through a first time infection or from reactivation) and is the leading cause of viral infection at birth in the US, causing birth defects.  

Most people have been infected with EBV (Epstein Barr Virus), which can cause a mono-like illness and which can also surprise us later on affecting our health (even very seriously with Lymphoma or when facing cancer treatment).

By the way, there's something smaller than viruses, prions. They are something we know even less about.

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