biologydirect | The variety of parasites that can affect host behavior suggests that the phenomena of parasitic host control might be more common in nature than currently established and could have been overlooked in humans. This warrants a detailed search for parasitic organisms that affect human behavior. One approach to search for “invisible” microbes that influence behavior is by comparing the microbiomes of control subjects and humans that consistently engage in irrational ritualistic behavioral activities, which contribute to the spreading of parasites and infections.
The modern anthropological view on religion is that it is a cultural meme that replicates through social communication [44]. While the meme itself may influence behavior, religious icons are known to be vectors of infectious diseases [45]. Most major religions have rituals that are likely to promote the transmission of infections. This includes circumcision [46], Christian common communion chalice [46], the Hindu ‘side-roll’[46] and Islamic ritual ablution [46] as well as the Hajj congregation in Mecca [47]. For example, the latter is specifically associated with outbreaks of meningococcal disease [48].
Also many religions are centered on sacred relics that are worshiped and frequently kissed by multiple people and thereby can act as vessels for microbial transmission. Crosses, icons, Bible covers are kissed in some denominations of the Christian tradition, the Black Stone (the eastern cornerstone of the Kaaba) is a relic that is kissed by millions of Muslims, kissing of the Wailing Wall is a religious tradition for the Jewish. It is unlikely, but possible that the rejection of condom use, vaccination and use of antibiotics present in some religious cultures, as well as the sacred status of specific domestic animals (possible definitive hosts to the parasites) may also be related to microbial host control. Finally, it has been noted that many parasites eliminate their hosts reproductive potential as they channel all available resources to maximize their own reproductive success [18]. Coincidentally celibacy is commonplace for holy individuals that are most devoted to their faith such as monks or nuns.
Thus it is possible that various religious practices could represent biomemes: manifestations of a symbiosis between informational memes [54] and biological organisms. This concept is somewhat similar to the fictional midichlorians of the Jedi Order from the popular series “Star Wars”[55].
Two particular parts of the human body seem to be most promising for the search of behavior-altering parasites. First of all, the human gut microbiome may be of interest in light of the microbiome-gut-brain axis concept. Another promising area to search for behavioraltering parasites is the human brain. Several organisms that can bypass the mammalian blood–brain barrier and produce a latent infection without obvious symptoms are currently known. In mice with latent toxoplasmosis, Toxoplasma gondii cysts can be found in various regions of the brain, especially in the olfactory bulb, the entorhinal, somatosensory, motor and orbital, frontal association and visual cortices, the hippocampus and the amygdala [56]. In humans the brain also appears to be an important site for Toxoplasma gondii cyst formation and the parasite is capable of infecting a variety of brain cells, including astrocytes and neurons [57-59].
