Today, rather than writing a review, I will be going through an analytical approach to a certain element of Focus Home Interactive and Asobo Studio's A Plague Tale: Innocence.
Be fairly warned: spoilers follow regarding the latter half of the game.
The element being examined is the Prima Macula, known through the game as the blood-borne connection that Hugo de Rune and others before him have to plague-bearing creatures, most notably feral rats, enabling them to exert telepathic control over the creatures to manipulate movements in their frenzy, as well as being able to see into their minds on some level to sense them when they are near.
According to a brief exchange with Narrative Director Sébastien Renard, it seems entirely possible that while the Prima Macula in 1348 France has concentrated control over rats that spread the bubonic plague, previous wielders (and subsequent ones) may have had control over other creatures declared as vermin. To use his words exactly, "Well, swarms of animals have always be a tradition among plagues, such as in the Plagues of Egypt. I can only say that our version is the rats, and let you imagine what you'd fear more :) (yet in France today, it would definitely be mosquitos! :D)"
If taken to its logical conclusion, plenty of animals could be controlled, from birds to insects to much more. Similar to the plague rats of the original Dishonored being comparable to the bloodflies of Dishonored 2 in function for an epidemic-ridden society and how someone developing their powers in one era or another would be connected to their own time and place's source of infestation, users of the Macula in other time periods could utilize their power over infected creatures to perform acts like creating a temporary artificial darkness in the form of thousands or even millions of insects or birds (if they are not afflicted with the same light sensitivity as the rats), capsize and sink watercraft through fish, or even control larger land animals than the waves upon waves of rats encountered by the de Rune children and their friends.
Similarly, the locations where said animals live would be drastically different. The gore-filled tunnels of the rats are a hint of the kind of macabre living spaces these creatures live within, but what if they were in trees as nests, or otherwise lying in wait in places at a significant height that would make it harder to spot them until it is too late?
That said, all of this may be completely inaccurate. The main element that may make this speculation invalid is a look at the historical pathology related to the Prima Macula as known within the story. Research in-game places the earliest known account of the hosts for the Prima Macula at the time of the Plague of Justinian (541-542 CE) in the Byzantine Empire, a disease that has been since confirmed as originating from the same bacteria (Yersinia pestis) as the aforementioned Black Plague (1347-1351 CE), and thus all fitting under the collective label of "plague" in terms of epidemics.
If Mr. Renard's denotation of the Macula as for "plagues" rather than all epidemics is accurate and not just a general colloquialism, then the applicability of when and how this type of power is used would be greatly limited, mostly just to rats and perhaps fleas, as there does not seem to be direct control that bearers of the Macula have over species that are infected by said rats. However, none of this is to say that the spread of the Macula would be too inherently limited. There have been many plagues throughout history, numbering greater than forty.
The existence of such a significant element as the hosts of the Prima Macula give rise to the idea of how it could potentially alter the way in which society develops if it were to be known to higher authorities, as demonstrated by Vitalis Bénévent's goals within the game itself. First it seems prudent to go over what is known about how to control the Macula.
Control over the Prima Macula relies upon certain "thresholds" through which the host experiences a lot of pain until their body can become accustomed to the power, coupled with symptoms such as times of significant weakness and some rather high fevers. Certain alchemical concoctions are capable of controlling these thresholds, such as the ones used by Béatrice de Rune and her fellow alchemist Laurentius, but only with the help of the large book known as Sanguinis Itinera ("Voyages of the Blood") was such an elixir completed. Another component important to the Macula's progress appears to be internal, related to moments of intense emotion such as heightened fear or anger, but these elements can be worked through by having someone close by to manage said fears, and are much less important once the host passes the final threshold to the point of being able to control the rats, which also appears to allot a kind of passive immunity to the plague itself through rats' unwillingness to attack said host. Whether or not this type of issue would be a significant problem for people who are older than the five-year-old Hugo is unknown, but perhaps it is a recurring element.
As shown by the alchemical works within the Inquisition, some other scientific means have been used to transmit the Prima Macula. A blood transfusion from one who has a hereditary form of the Macula to someone who does not grants a connection through their blood. The artificial host is granted power over the infected creatures at the same rate as the natural host, even crossing the thresholds in tandem. Whether or not artificial hosts suffer from the same debilitating effects as those for natural ones is unknown, but as shown by Hugo de Rune's transfusion to Vitalis Bénévent and the eventual boss battle, not only is the natural host able to sense the Macula within the artificial one, but he or she is also capable of understanding if the Macula, which appears semi-sentient (unless Hugo is wrong) is "fighting" the artificial host in some way to prevent the use of power.
Certain elements, such as the "exsanguis" substance procured from rat-infested locations and the resultant "odoris" alchemical substance utilized to draw rats into one area or another, help to give the impression of non-carriers of the Macula having some defense nonetheless, albeit one that is rather dangerous to procure and utilize. Similarly, the specially treated white rats, which respond only to Vitalis and not to Hugo, along with being immune to bright lights or fire, show another way of controlling the use of the ability itself.
All of these elements come to a head when thinking about the implications for said developments going forward.
In terms of developments to society, such scientific works could be used to manage or even neutralize the effectiveness of potential hosts of the Macula, especially with the increase in scientific knowledge since the 14th century CE. For instance, if such a serum were created, it could help to keep such a horrific superhuman from emerging, or conversely be even worse and attempt to heighten emotional extremes to keep them down with their own sickness. Neither of these are benevolent options, to be clear, but both seem within the realm of possibility for the game.
Through the experimentation of Vitalis Bénévent, it is shown that while there are drawbacks (even excluding the difficulties with blood transfusions in general), it is entirely possible that people could create more carriers of the Macula while keeping the natural hosts safely away. Between the transfusion technique and the unusual white rats, plague-based officers are entirely within the realm of possibility for the later years or centuries of the story's narrative.
Meanwhile, elements like exsanguis and odoris show how society could develop other means to control the infected creatures through a variety of inventions to redirect or otherwise neutralize them even outside of common exterminators or plague vaccines. Together with the aforementioned officers, not to mention more positive uses such as redirecting plague vectors away from population centers to limit infection, there is an enormous amount of potential at work.
Of course, all of this could be for naught, as it is not clear whether or not A Plague Tale: Innocence will have any further stories in its universe, but much like another disease-related game published by Focus Home Interactive, Vampyr, all of this serves as an interesting thought for what could potentially exist moving forward.