Microorganism and disease lore from ESO (some Necrom spoilers).
Some of the new lore we got in *ESO Necrom* clarifies how certain aspects of the world of TES such as microorganisms and how contagious disease works.
Both in the recent content and some of the older releases we've gotten information on this element of the world so I thought i'd compile some of the more interesting sources here.
This is non-exhaustive and will not go into overtly magical afflictions such as vampirism and lycanthropy, or into the more arcane phenomena that it is shown can sometimes accompany plagues and such when something like the influence of Peryite and his cults is involved.
That said:
Within the Telvanni Peninsula lies Tel Dreloth, the tower of Telvanni Master Sathile Dreloth where Dacia Caro believes Sathile is holding her own son prisoner. Dacia and Nathyn are in love and were planning to escape together but before they could do so Dacia was dismissed from her position in Sathile's employ and hasn't been able to see him since.
The Vestige agrees to help Dacia traverse the tunnels that cross underneath Tel Dreloth so that she can get to the Isolation Tower, where Nathyn is being held but upon entering the structure it rapidly becomes clear that Sathile is the least of their problems,the place is abandoned and Dacia mentions how permanent arcane barriers should have been present throughout the complex but have somehow disappeared.
Within the tunnels the pair are attacked by both strange animals (bears, senche, wolves) that have become entirely consumed by some sort of fungal growth (to the point they appear similar to the creations of Mycoturgy, fungal golems even though they aren't the same) and the infested bodies of the Tel Dreloth researchers who are likewise consumed by said growth and are, like the animals, being controlled into attacking.
[https://en.uesp.net/wiki/Online:Afflicted\_Bear](https://en.uesp.net/wiki/Online:Afflicted_Bear)
[https://en.uesp.net/wiki/Online:Afflicted\_Researcher](https://en.uesp.net/wiki/Online:Afflicted_Researcher)
[https://en.uesp.net/wiki/Online:Afflicted\_Wolf](https://en.uesp.net/wiki/Online:Afflicted_Wolf)
[https://en.uesp.net/wiki/Online:Afflicted\_Senche](https://en.uesp.net/wiki/Online:Afflicted_Senche)
The last surviving Tel Dreloth researcher, an Argonian named Tun-Shei, explains that everyone except him is in their current state because one of Sathile's test subjects named "Delmon" got loose and caused all this damage by releasing toxic spores of some sort.
[https://en.uesp.net/wiki/Online:Tun-Shei](https://en.uesp.net/wiki/Online:Tun-Shei)
Here Dacia will mention that, according to what she's learned from the Tel Dreloth researchers, diseases *"like flu or fever"* spread through tiny particles that are too small to be seen with the naked eye.
The same goes for fungi like molds and mushrooms and the same goes for Delmon.
>***Sathile is testing some sort of cure, and has notes on some toxic spore interfering with her wards.*** > >***"Spores? The researchers spoke of those. Little seeds on the air, invisible to the eye—like flu or fever. I think that's how molds and mushrooms make more of themselves.*** > >*"Delmon Spore Sample." Delmon, Delmon. What is that? It sounds like a name."*
[*https://en.uesp.net/wiki/Online:Dacia\_Caro*](https://en.uesp.net/wiki/Online:Dacia_Caro)
Delmon is also Nathyn, or rather Nathyn is Delmon's host body.
So what is Delmon ?
Delmon (named for Sathile's husband who died to the Knahaten Flu) is a form of fungus, originally discovered within a *"pool of brackish water"* in Black Marsh by Tun-Shei, who brought it to Morrowind so that Sathile (whose research revolved around discovering ways to cure illness and primarily the Knahaten Flu which was wreaking havoc across Tamriel at the time and was seemingly incurable) could use it to create a cure.
Sathile discovered the following:
1 ) Delmon is a sort of fungal symbiote, when properly prepared it can be inoculated into a living host without damaging them. The symbiosis is seemingly permanent and irreversible, the fungus spreads itself across the internal organs (the core of the growth being the lungs) and Sathile knows of no way to remove it.
2 ) Whenever it feels threatened (or deems something a threat to it's host if it has one), whenever it senses fire or smoke, or simply to reproduce, Delmon releases clouds of toxic spores into the air, like *"Little seeds on the air, invisible to the eye"*.
3 ) The Delmon spores cause rapid necrosis into all non-fungal life they come into contact with, the degree of toxicity and speed of the necrotizing process is variable and adjusts depending on how threatened Delmon is and how intense the emotions it's host is feeling are.
The spores are so toxic that even viral microorganisms like the Knahaten Flu are completely eradicated by it, this is how Delmon can be a "cure" for things like the Knahaten Flu, it kills every single bit of the disease it deems an intruding presence within the body of it's host.
Upon disposing of all "threats" Delmon's spores will rapidly grow throughout their bodies and control (reanimate ?) them to repel other dangers (the fate that befell all living creatures in Tel-Dreloth and the tunnels except Tun-Shei and the Dreloths).
Sure enough, Delmon eradicated the Knahaten Flu in Nathyn's body without issue.
4) Delmon's spores appear to have some sort of ability to interfere with magic, when Nathyn became distressed at the thought of not seeing Dacia again the spores were released with increased ferocity/toxicity and overwhelmed Sathile's containment barriers, forcing her to gather all her power to make a smaller/stronger one (this is why all wards in the structure except the one currently containing Nathyn disappeared and even this final barrier is being disrupted/has trouble containing them).
5) Delmon has the ability to sense and recognize both other growths of itself (as well as their hosts should they exist) and things that are similar to it's host. Sathile isn't killed by the symbiote because it can somehow recognize that her body's composition is akin to that of it's host to such a degree that it doesn't see her as a threat. While additional details on what this alike composition means aren't given, the concept of a "gene pool" is mentioned in texts like *"The House of Troubles"* (so the most likely option is probably the one that first comes to mind, genetic similarity).
[https://en.uesp.net/wiki/Lore:The\_House\_of\_Troubles](https://en.uesp.net/wiki/Lore:The_House_of_Troubles)
6) Argonians are seemingly the only non-fungal life immune to Delmon's spores, though it is said even their immense resistance to toxins is taxed to it's very limit by Delmon (Tun-Shei himself survived exposure but can barely stand and has great trouble breathing).
Since Nathyn can't be allowed to leave the Isolation Tower for the sake of the world at large, the Vestige is given the choice to either convince Dacia to keep helping with research for a cure without direct contact with Nathyn or to allow Sathile (who I will note was the one to intentionally infect Nathyn with Knahaten just to see if she could cure him..) to introduce the Delmon spores into Dacia's body like she did to Nathyn's so that they can be together (though Dacia too will need to be put in containment).
[https://en.uesp.net/wiki/Online:Nathyn\_Dreloth](https://en.uesp.net/wiki/Online:Nathyn_Dreloth)
[https://en.uesp.net/wiki/Online:Sathile\_Dreloth](https://en.uesp.net/wiki/Online:Sathile_Dreloth)
[https://en.uesp.net/wiki/Online:Sathile%27s\_Research\_Notes](https://en.uesp.net/wiki/Online:Sathile%27s_Research_Notes)
This reference to the concept of microorganisms existing and being responsible for disease echoes some older quotes from *Shivering Isles* where some characters would mention that certain utensils should not be used for fear of germs being on them, how certain places shouldn't be visited for fear of disease floating through the air and the role of hygiene in preventing it.
The term has also been used by Divayth Fyr, though not in the literal sense.
>*How can Thadon drink from that Chalice? Who knows what germs are on it?*
[https://en.uesp.net/wiki/Shivering:Sickly\_Bernice](https://en.uesp.net/wiki/Shivering:Sickly_Bernice)
>*We can go in? Well... I better stay here. There's no telling what kind of diseases are floating around in there."* > >*Sickly Bernice's isn't a bad place. Just make sure to wash your hands.*
[*https://en.uesp.net/wiki/Shivering:Felas\_Sarandas*](https://en.uesp.net/wiki/Shivering:Felas_Sarandas)
>*"Though your question is poorly stated, there is a germ of sense in what you ask.*
[*https://en.uesp.net/wiki/Lore:Divayth\_Fyr\_Answers\_Your\_Questions*](https://en.uesp.net/wiki/Lore:Divayth_Fyr_Answers_Your_Questions)
And in the same vein texts such as the *"Plague Concocter's Instructions"* from Bastion Nymic reference diseases having various strains as a known factor, Crimson Rot and Blood Plague are of similar strains for example and Peryite's cultists are expected to know of such things when concocting their plagues (also modifying them to exhibit traits like delayed symptoms so they can spread further before they're discovered and such) or making offerings to Peryite.
[https://en.uesp.net/wiki/Online:Plague\_Concoctor%27s\_Instructions](https://en.uesp.net/wiki/Online:Plague_Concoctor%27s_Instructions)
[https://en.uesp.net/wiki/Online:Research\_of\_Nathien\_Mortieu](https://en.uesp.net/wiki/Online:Research_of_Nathien_Mortieu)
Speaking of Peryite, the text *"Deal with a Daedric Prince"* also suggests things like the air, water, or insects can serve as vectors of infection, as well as the use of measures like burning infected bodies.
Granted in this case there is a more arcane element because Peryite is involved directly (a heavy miasma descends on the city of Tear, it's waters turn foul and swarms of flying insects fill it, infecting the whole city with all sorts of diseases) but, though there is intent behind the intensity and variety of infections, the means by which they spread remain the same, and diseases spread specifically include things like the grippe and ague (barring the disease afflicted on the author directly for angering Peryite which somehow makes his body transform and his corpse move even as he burns, of course, which is pretty supernatural).
[https://en.uesp.net/wiki/Lore:Deal\_with\_a\_Daedric\_Prince](https://en.uesp.net/wiki/Lore:Deal_with_a_Daedric_Prince)
The Sload also spread the Thrassian Plague by infecting marine life across Tamrielic coastlines, it is also said to have been spread by infected gastropods and to have infested *"every drop of water"* in afflicted areas.