The books propose some rather off-beat lore ideas and story hooks, especially concerning the Kothringi culture.
Artificial Diseases Vol. 1: Slug-Famine
A Treatise by Mar Bekorithi
Diseases are worldly things, to be abjured or endured by worldly means. Some consider the existence of sickness a test of the gods. If this is true, then those who test us also give us the means of overcoming these trials.
The same cannot be said of those diseases of an artificial nature, devised by mortal sorcerers as weapons of war. An exquisitely delicate form of magic, the creation of plague is considered by some to be the alchemical Cala, the black fulcrum of their arcane school.
The most well-known of such diseases was the Thrassian Plague, a curse of Sloadic origin which struck the western continent during the waning years of the First Empire. Little is known of its creation, symptoms, or vectors of infection. The pandemic began on the Abecean shores and was carried inwards along the trade routes, suggesting a long refractory period. Some called it the slug-famine, as it was said to interfere with the body's ability to derive nutrients from food -- folklore claims those infected were ravenous with hunger and thirst, wasting away even as they gorged themselves.
The plague spread across most of Tamriel, claiming over half of the known population before a cure was devised in Alinor. Even then, the disease lingered with what some argued was a sapient intent, flaring up unpredictably during the troubled periods of war and chaos that followed.
What moved the Sload to create this pestilence? Bendu Olo and his All-Flags Navy regrettably did not bother with interrogations. Many assume that the Sload were guided by greed, longing to plunder the riches of vacant empires and enslave their populations. Those Sload who, despite Imperial censure, continue to dwell in the ports of Tear, Senchal and Argonia claim that their ancestor's motivations are as obscured to them as to us, given that the sinking of Thras destroyed almost all of their First Era culture.
The recent validation of historical "Middle Dawn" theories has led to a new theory, namely that the Sload saw their actions as a retaliation. The Dragon Break was no doubt traumatic for a race known for their pathological caution. Rather than risk this happening again, the Sload may have released their disease in the hopes of toppling the civilizations responsible.
This was not the last time that the Sload were associated with the brewing of plague. Rumors in the Iliac Bay claim that the Sload are capable of producing many such "bespoke diseases" -- plagues that target only a certain bloodline, or even a specific individual. Despite investigations of provincial and Imperial authorities, no example of such alchemy has ever been uncovered.
Artificial Diseases Vol. 2: Knahaten
A Treatise by Mar Bekorithi
The archives of the Museum of the Provinces contain a particular merchant's letter from the city of Stormhold. Besides humdrum details of tarriffs and caravan routes, it mentions a rash which has afflicted some of the firm's laborers, causing delays in production. The merchant ends his note with a promise to make up for lost time and money, next month. Two weeks later, he and all those mentioned in his letter would be dead.
The Knahaten Flu was by far the worst plague of the Second Era, responsible for numberless lives lost as well as the annihilation of several proud cultures of the Argonian region, such as the Kothringi and Lilmothiit. Popular history blames the Argonians for its creation, as they alone proved immune to it.
A somewhat obscure theory posits that the Knahaten Flu was spread not through air, dirt, water, or vermin, but through silver. The Kothringi were known far and wide for their silver mines. Kothri silver financed the Alessian Empire's sectarian wars, and supported the Reman conquests and the decades-long war with Morrowind. It is estimated that a fourth of the currency in circulation under Emperor Brazollus Dor originated from the depths of Koth.
Besides silver, disease has always been closely associated with the Blackwood marshes. Other human populations, such as the Orma, bear the marks of living in their proximity, suffering from severe deformities such as blindness.
The Kothringi, by contrast, were curiously hale and healthy -- in fact, many sources emphasize their physical beauty. Even the respiratory illnesses that befall miners of all kinds eluded them, despite the fact that most Kothringi would spend a year in ritual service to Z'en, deep in their holy mines.
Rivers that became polluted with runoff from the mines glowed white at night, causing fish to die and animals to turn feral. Diseases multiplied like flies. Even plants grew poisonous and strange. Whatever curse lived in the heart of Blackwood, the mines of Koth were near the heart of it.
Was it greed, that cursed the Kothringi? Certainly this is not the first time that a sickness rested within a physical item. I am reminded of the story of a Breton village of the Second Era. It is said that, for some unknown offense, an alchemist had taken a great dislike to this place. Knowing the villagers' rustic lifestyle, he enchanted a great amount of baubles, and, posing as a common peddler, sold these to the villagers.
Unbeknown to them, each item was enchanted in such a way that it would capture and concentrate ambient diseases. Plagues quickly burned through the village, its inhabitants ignorant of the cause of their misfortune -- some even clutching their jewels in the throes of death, or passing them on to their children on their dying bed. The village was lost, but looters and refugees carried off many of these items, some of which are still at large within High Rock.
Though this example does not concern a artificial sickness, it does show how such a disease could be spliced onto a common material. Considering the nature of Kothri silver, which was very pure, homogeneous, and capable of holding great enchantments, it is possible that contact with silver, thus infused with the Knahaten Flu, infected not only those who came into contact with it, but also other pieces of Kothri silver in the vicinity. Commerce, then, would have been the vector for this sickness.