Physiology of a heart hijacking parasite?
This is a question regarding my little critters that hijack of their victim. By doing so they get direct access to a steady flow of nutrients through the bloodstream and get shelter with optimal temperature and humidity with the added protection of a ribcage. What's terrifying about these little bugs is that you can't get rid of them, because they've highjacked the one organ that keeps you alive.
What kind of physiology would a heart parasite have?
This question is not asking "would this evolve" as this creature is already very complex, it performs a risky procedure as part of its life cycle on mere instinct, which is not something your typical leech or tick does. A more pertinent question is what kind of body they should have to make this work? They must first burrow into a host without inflicting a life threatening injury. Then they must attach to a still beating heart and drain sustenance through the blood. They might go through multiple life stages like a larva for burrowing and a crab for latching on the heart.
What do you think?
Edit: The definition of hijack is "seizing" something, in this case that would be the heart. The parasite does not replace the heart itself, but laches onto it.
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1 answer
As @vodolaz095 mentioned, this isn't something that could happen quickly - @John O's answer points out a lot of the issues that show up there.
There is a parasite that does something marginally similar - Cymothoa exigua. This lovely parasite will sever the blood vessels in the fish's tongue, causing it to die and fall off, at which point it attaches itself to the nub and becomes the fish's new tongue.
Obviously, this approach can't work 100% with a heart. Sever the blood vessels to it and you get death. However, a similar approach could work.
The parasite, small-ish, enters the host's body, where it finds its way to the heart. At that point, it attaches itself to one or more blood vessels, where it grows. At some point, it is attached to all of the blood vessels, and begins constricting the blood vessels of the heart, which will then atrophy and die while the parasite takes over.
This would be a gradual process - I'm guessing weeks, maybe months, instead of days or hours. And it would likely be highly painful - A modern society would have someone go to the hospital for heart pains, get a CT scan or MRI, and it would likely be early enough to remove it. Earlier medicine probably wouldn't be able to do much about it - And eventually, the pain would probably go away as the heart died.
I'm not a biologist nor a doctor, but I think that the creature might even be able to react and adjust heart rate depending on things like oxygen levels in the blood, removing or reducing the need for interacting with the nervous system.
Additionally, the way this creature pumps blood could be entirely different to how the human heart works, leading to a different sounding heartbeat or even a different-feeling pulse.
In the end, once the creature is there, it's in the interest of both it and the host to maintain the host in a healthy way, so beyond the initial pains of heart implantation, it would likely not be noticed and the person would be able to live a normal life. Depending on how you want to go, it could even offer a boost to the host's immune system against things like other parasites and, specifically, blood-borne pathogens.
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