What we know:

I think from Pottermore/canon context we can safely say that lycanthrope was meant to be a metaphor for HIV and the AIDS epidemic.

With that, we can think of lycanthrope as an illness caused by a virus. The virus (lycanthrope) is transferred through a bite on the full moon. Bites not on the full moon either:

A) do not transfer the virus, or

B) transfer the virus, but not in high enough quantities to permanently alter the DNA** to the levels in which full lycanthrope occurs.

I choose to go with option B because we have Bill who was bitten not on the full moon and he developed a liking for "rare" steaks. I also headcanon that the moon cycle affects Bill's mood, but not to the full impact that Remus would have. Long-term ill-effect to me means they are not a wolf but to each their own. The rare stakes comment does indicate there is some alteration to Bill's DNA.

If you are wondering how is it possible someone could have a virus but not have the illness - these people would be asymptomatic carriers. Now, scientifically, asymptomatic carriers can still transfer the illness, however, you need to have a high enough viral load to transmit an illness. Meaning, that asymptomatic carriers would be less likely than symptomatic individuals to spread the virus if they have a low viral load.

You might be thinking that asymptomatic carriers should experience no symptoms as they are asymptomatic. However, there is still much we do not know about asymptomatic carriers and it is possible, depending on the disease, for people to develop later-stage disease symptoms.

So to me, asymptomatic carriers (those bitten not on the full moon) would be unable to 1) transfer the virus to others via a bite*, or 2) have the full impact of the virus.

Viral load means the amount of virus. Think about how COVID tests you would have a bright line vs a light line for positive. When you are very sick that line is popping, but as you get better the line fades. This is an indicator of the amount of proteins related to the virus and the total viral load you have. When you have a high viral load transferring the virus is much easier than when it is lower. This is why you stay home when you are first sick as you are most likely to get other sick then.

Viruses have a replication process, what this means is they infect cells and create more viruses. In most illnesses, your body fights the infection and kills all the cells that have the infection so you no longer have it. For other viruses, like HIV, they are much better at avoiding your immune system and staying around. There can be peaks of viral expression with these viruses that are good at avoiding your immune system (another example would be herpes and outbreaks).

Someone with lycanthrope would be constantly fighting the virus. However, the body would be unable to protect itself fully and that is why flare-ups (full moons) occur. We can think of the full moon as the peak of infection (high fever, delouses, the worst you have ever felt). Before and after flare-ups of a virus are very taxing on the body and this is why lycanthrope would feel poorly before/after a full moon.

For lycanthrope, this timeline of replication/high viral loads occurs with the full moon. Basically, the viral load is highest when the moon is full. This is why the person changes into a werewolf and why they can transfer the disease at that time. It would also be why they cannot convert people to werewolves when the full moon is not happening as they don't have a high enough viral load.

What does all of this mean for the lycanthrope virus?

*Can they transfer the lycanthrope via gametes (sperm/egg) is another question.

Epigenetics

Epigenetics refers to how the environment can cause changes that affect the way your genes work. Epigenetic changes are not permanent (this would be a mutation). The main mechanisms of epigenetics are DNA methylation and histone modifications. There is a lot of debate on the extent epigenetics can be inherited by offspring (epigenetic inheritance).

Part of the environment can be a virus that is in your body.

When you are infected with a virus it can alter your DNA via epigenetic changes - these then impact your cellular gene expression patterns. In shorter terms, a virus can change how your body interprets your genetic code.

The viral load you have can impact the extent to which the epigenetic changes occur.

Now I mentioned that the virus would still be transferred to those who are bitten not on the full moon, but they would not have enough virus to impact their DNA to result in the full transformation (**), and instead, they would become asymptomatic carriers.

WTH do I mean by there is not enough virus to cause the full transformation?

Since the viral load is lower in an asymptomatic carrier their DNA epigenetic changes would (most likely) be lower. And since epigenetics are transient, the body would be able to be repaired faster (in theory), and the person would remain asymptomatic - but maybe some things pop up because there are still epigenetic changes that occur (like wanting rare meat).

Conclusion - the lycanthrope virus causes epigenetic changes to the DNA resulting in the effect (turning into a werewolf). Those who are asymptomatic carriers do have epigenetic changes occurring, but they are repaired fast enough due to not having enough of a viral load.

Now can the lycanthrope virus be passed on?

We have a little more to go before we can get to this question.

Mutations

We have another option of how to think about werewolf genetics. And that would be that the bite changes the DNA of a person with lycanthrope. Meaning they have a mutation in their DNA.

DNA mutations can occur from a virus. The best example of this would be HPV being linked to cervical cancer due to the impact it has on cell division - this is why getting the vaccine is so important.

So it could be that the lycanthrope virus causes a mutation in the DNA which then results in the full werewolf form occurring.

The mutation occurring would also depend on the viral load. So this would still follow the idea that the viral load would be the highest during the full moon and be the reason why the disease would be spread.

What would this mean for someone with full lycanthrope vs asymptomatic:

All The Changes

If you want it to be a mutation or an epigenetic factor you can pick - or you can do both. I think the answer is that both are occurring.

My reason why is that genetic mutations are a permanent change. Epigenetic changes are transient.

The best comparison I have is that with HPV you have the virus and epigenetic changes can occur, however, if you are unlucky then a mutation can occur and you get cancer.

Those who are bitten not on the moon have the virus and epigenetic changes occur which creates the rare meet effect, however, those bitten on the full moon get cancer (lycanthrope). The cancer (lycanthrope) comes with both the full moon change (mutation) and the side effects of rare meat (epigenetic).

At this point you are probably screaming at me - but does it pass on?? We are almost there I promise...

Dominant vs. Recessive Genes

We are all made up of a combination of DNA from our parents. This means we have different alleles. Alleles are a variant of a gene. The common ones we consider are eye color, blood type, and hair color. There are dominant eye colors (brown) and recessive (blue).

You have to have both pairs of the recessive gene to end up with the received trait. (below is our favorite pundit square)

Epigenetic Inheritance and Vertical Transmission

Epigenetic inheritance occurs when an offspring inherits an epigenetic modification like DNA methylation or histone modification. Vertical transmission occurs when an offspring inherits a virus from a parent.

Epigenetic inheritance is such a dumpster fire that I leave that up to the genetic gods. Now, vertical transmission can be prevented, and it is often done by viral suppression. This is why the risk of transmitting HIV to your baby can be less than 1% if properly treated.

There is a difference between transferring the virus and transferring the genetic mutation.

Now one question I have is if the virus can be transferred via bites - why is it not transferred via sex fluids/blood.

I think you have options:

Option four has the most canon evidence, as shown by 1) Bill's injuries, 2) Tonks not having any symptoms, and 3) Pottermore.

An argument can be made for number three.

Pottermore uses "attacked" to describe someone who then gets wolfish tendencies, while pointing out that an unintentional scratch would leave a scar. This could be an indicator that intent matters.

Scientifically, it really does not make sense for a virus to only be transferable via saliva. Maybe it's magic, but I could understand if sexual fluids and blood could transmit the virus (you decide if the fluids have to enter the bloodstream or if it can be an STI).

If you want to go the route that the virus spreads via sexual fluids.

For Remus - if you impregnate someone when your viral load is the lowest, you would have the least likely chance of giving the virus to the person you are having sex with. This does not mean the sperm could not carry the mutation lycanthrope, it would just put the partner at lower risk. ALWAYS USE PROTECTION!

For someone carrying a child who is a werewolf, taking wolfsbane potion (antiretroviral therapy) would lead to viral suppression and a lower risk of viral transfer to the fetus.

Is lycanthrope transferable to children?

To recap:

Lycanthrope virus is transferred to those who are bitten.

Now, if we do have mutations, the question would be -> does the mutation also impact the gametes (sperm/egg).

Based on all that I have stated above about how this virus would work, the answer would be yes for those who have full lycanthrope.

If we operate under the assumption that lycanthrope permanently alters alleles that are recessive and transferable (eg. alters gametes) . Then it would require two parents to have a recessive gene for lycanthrope.

This would mean that it would be impossible for Remus to transfer over his lycanthrope, as Tonks does not also carry the recessive gene. Example of this would be cystic fibrosis and sickle cell anemia.

If lycanthrope is the dominant gene, then there would be a 50% chance that a child would have lycanthrope. This would be similar to Huntington's disease.

The evidence from Pottermore would be that the virus causes a recessive genetic mutation. The key here is that they have kids with human partners.

^I take this to mean they are not werewolves, not that they have no symptoms at all, but you could absolutely read it the other way.

Now, here comes the harder question. If someone is an asymptomatic carrier could their gametes be altered by the virus so that some of them carry the mutation -> Yes this could happen. Gametes are extremely sensitive cells to the environment (eg a virus).

Teddy Lupin - most likely has a recessive gene for lycanthrope. Teddy would 1) have symptoms like an asymptomatic carrier, but not change or 2) have no symptoms.

Victoire Weasley - could have epigenetic inheritance (debate my people!). It could also be possible that she recessive gene for lycanthrope - which would put her in a similar position to Teddy.

Now what will happen to Tedorie kids? There could be a 50% chance of them having lycanthropy if Victoire and Teddy have the recessive gene.

My Take

I personally go with the idea that:

1. A full moon bite leads to the person receiving enough of a viral load to create a mutation of their genetic code causing lycanthropy. In addition, epigenetic changes occur that impact their life (rare meat, mood, health, etc.)
2. A bite not on a full moon, means they receive the virus, but at a low viral load so they are asymptomatic carriers. Their genes might be impacted by epigenetic changes. However, they would not have enough viral load to transfer the virus to another person via a bite. Nor would they have a mutation.

I also think that the virus must be transferred via saliva to blood. No other combination would allow the virus to transfer. I do this for simplicity, and as it tracks more with what is on Pottermore/the spirit of werewolves.

I think that Teddy would have a recessive gene and it would present as an asymptomatic carrier. I don't think that Victorie would have a recessive gene due to epigenetic inheritance (a debated concept).