Twenty Years Later- Yutaka's Youkai Biology
Chapter 5: Youkai Endosymbionts- Domain Bacteria
Though this textbook is supposed to deal with humanoid life, it should be noted that sometimes, organisms not technically part of a certain morphology can still express, change or control things of said morphology, such as the infamous Cordyceps fungus (Costandi, 2006). In this case, the endosymbionts in question tend to infect humans, or otherwise humanoid creatures (Cox, 2004). Contrary to popular opinion, symbiosis does not refer to positive interaction between host and symbiont alone, instead, it can be mutualistic, parasitic, commensal, obligate, or facultative (Martin & Schwab, 2012). However, the main sort of endosymbionts that I shall cover are the obligate endosymbionts found in some members of Homo sapiens sapiens, namely the endobacterium Lamia intorium, otherwise known as 'vampirism' (Bunsen, 1993).
Vampires, contrary to some unreliable sources (Meyer, 2005), do not sparkle, nor do they have a differing species to humans to the point where hybrids would result in hybrid vigour (Dawitsu, 2017). Instead, the endobacterium Lamia intorium invades vampiric humans' gametes, rendering vampires either infertile, or, if bred with other vampires, entirely vampiric offspring (Hadekawa, 2025; Pile, 2005). However, in many cases of vampirism, gametes are unable to be formed altogether, and so their main form of reproduction comes not from sexual reproduction, but transference of Lamia intorium via injection of the symbiont into a potential host's blood (Bartlett, 2005).
The reason why blood is the preferred tissue for Lamia intorium to enter is due to the lack of nuclei in the red blood cells of mammals (Gregory, 2001), enabling the otherwise poorly-adapted symbionts from having to destroy and alter the pre-existing nucleus (Stoker, 2010), something they require the resources of their host's cells to successfully perform (Wallin, 1923). Given the destructive and invasive nature of Lamia intorium, it would seem intuitive to label it as a disease, a parasitic endosymbiont (Stoker, 2003), however, with complete overtaking of the host body, Lamia intorium can be a rather useful symbiont, being almost mutualistic in nature (Stoker, 2003).
The traits of a completely Lamia-infected human (otherwise known as a 'vampire') include extremely slow decomposition despite host's technically deceased nature (Bunsen, 1993), continuation of the brain's functions and processes past time of host death (Stoker, 2003; Stoker, 2010), extremely quick reflexes, high muscle twitch speed (Bunsen, 1993), and for unclear reasons (Hadekawa, 2022) the ability to transform into a bat-like form (Bartlett, 2005; Bunsen, 1993; Hadekawa, 2022). These are all rather advantageous to the host, as their brain's continued functioning enables them to live as the same 'person' and enjoy the powers at their disposal (Stoker, 2003).
However, the stomach lining and heart are exceptionally poorly maintained in a vampiric human (Hadekawa, 2025), meaning that the oxygen and nutrients required to keep the body functioning cannot be acquired by digestion and circulation, as in regular humans (Guyton & Hall, 2000). Instead, Lamia intorium alters the canine teeth to be hollow and lead directly to the blood vessels, enabling them to be haematophagus (Bartlett, 2005; Bunsen, 2005; Hadekawa, 2025; Stoker, 2003) and eliminate the need to digest, as the victim of the blood draining has digested for them. This system doubles as a means of transferring Lamia intorium into others (Bunsen, 2005), and the food is transported by a peristaltic circulatory system, the blood vessels contracting in a wave to accommodate for the malfunctioning cardiac tissue (Stoker, 1999). This unfortunately makes vampires heavily reliant on hunting creatures for blood, especially humans, as their blood is most similar to their body's requirements (Bartlett 2005; Stoker, 1999).
Aside from vampires, the only other case of Lamia intorium infection in humans is partial infection. This results in some tissue not being subject to Lamia's rejuvenating nature (Pulliam, 2006) and results in a partially decomposed, and if decomposed in the brain, intellectually lacking host known by most as a 'zombie' (Maçek, 2012). These are notably less sophisticated that fully infected hosts, and attempt to consume flesh to sate their hunger rather than blood (Pulliam, 2006). These attempts are futile, and unless their existence is continued by other magical means (Kaku, 2010), these hosts tend to die of starvation within weeks.
Thanks to their human hosts, Lamia intorium has become almost as successful an endosymbiont as its mitochondrial and chloroplastic ilk, and though not human, have contributed to the creation of one of the most well-known and feared (Bartlett, 2005; Bunsen, 2003; Meyer, 2005; Stoker, 1999; Stoker, 2003; Stoker, 2010) youkai 'races' of all. As such, despite not being technically humanoid, Lamia intorium and its hosts are a worthwhile topic to study, ideally in better detail that is being laid out in this generalist textbook.
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