Imagine an airplane. Good. Also imagine that a small metal shaving has lodged itself into a mechanism of the air-conditioning so that pieces of metal are fed into the spinning fans. This produces a huge pile of identically-shaped metal shavings; some fly off into the electronics bay. The size, shape and composition of the shaving is exactly so that the navigation is subtly, but precisely changed to cause the plane to veer ridiculously close to other planes. Cargo bay doors are also sabotaged, opening up and releasing a payload of metal shavings over other planes, hoping that one will lodge in the exact same place in its air-conditioning unit to start the cycle over again.
This sounds completely ludicrous, but the complexity is on par with what rabies virus exhibits every single day in its hosts around the world. How the hell does it does this?
A little about the virus and disease: Rabies virus (RaV) is an RNA-based virus that kinda looks like a bullet. It can theoretically grow in any warm-blooded host, but is usually confined to mammals, such as bats, dogs, cats, and also many livestock species. If you get it and do not get treatment, you will die. How you die is innately linked to how awesome RaV is, which will be outlined in the following scenario.
So you’ve been bitten by a sheep…
So a rabid sheep has mistaken you for a blade of tasty grass and has nibbled aggressively on your little finger. RaV in the sheep’s saliva floods the wound. Immediately RaV sticks to, enters muscle cells and replicates using the cell’s machinery. Meanwhile, you’ve healed up, perhaps tucking into a nice lamb rack to get your own back. You feel none the worse for wear.
Over the following weeks, the virus particles build up and enter the nerves around the area. RaV slowly inches up your arm (~2cm each day) via the long nerve cells, towards the spinal cord. It’s around this time that the body builds up an immune response and you start to feel general flu-like symptoms.
Once RaV has reached the nerves or spinal cord, then you’re really in trouble. The nervous system (and the central nervous system (CNS), in particular) is what we call “immune privileged”. This means that it’s very hard to get an immune response against cells in that area. There are many reasons behind this: first, the blood-brain barrier means it’s harder for immune cells to get into the spinal cord and do their thing; also, the cells in the CNS do not “talk” to the immune system as much as other cells, so the immune system doesn’t know if the CNS is infected; and moreover, the CNS cells actively express proteins that suppress the immune system in the area. So RaV is now in a good little hiding spot and can get up to all sorts of mischief.
As RaV replicates in nerve cells, bits of virus product clump together. These clumps alter the way the nerve cell fires off, either making the signal stronger or stopping it altogether. If we now zoom out to the patient-view, we see that you’re starting to experience pain or paralysis near the area of the bite due to altered nerve signals. As RaV works its way through the spinal cord, you get stomach cramps, violent muscular jerking, nausea, and breathing difficulties. There is now very little treatment we can give to you, the inevitably dying patient. OK, now it’s time for RaV to jump this sinking ship.
RaV spreads to all the tissues that the nerves lead to; muscles mostly, but also (more importantly) the salivary glands. This will act as RaV’s escape hatch. But how to get to the warm tropical lands of another host?
Some neurons in the brain are also altered, although we still don’t exactly know how. 50% of the time you get paralytic rabies, where you become completely limp. Perhaps this makes you more susceptible to attacks from predators, allowing RaV in your bodily fluids to spread that way. The other 50% of the time you get furious rabies, where you become hyper-aggressive and bite other people. This has the obvious benefit of spreading RaV to any animal (or human) you may bite in your rage.
Apparently this isn’t enough for RaV; just to top it off, RaV will also paralyse the muscles that are responsible for swallowing, so that you don’t swallow the RaV in the saliva or dilute it out by drinking water. This produces the distinctive foaming at the mouth you see in rabies patients.
So in summary, RaV has turned your body into its own factory and even convinced you to spread the products to other people by altering your behaviour. That’s pretty kick-ass. You know, you could have stopped all of this if you just got vaccinated with rabies. The development of the vaccine is a wonderful story on its own, which I’ll end with.
On Louis “Kick-ass” Pasteur
Louis Pasteur, between proving germ theory, immunising against anthrax and generally being a badass scientist, thought it would be a good idea to cure rabies, seeing as it was a death sentence to anyone who got it. He worked with Emilie Roux and probably some poor forgotten lab technicians during this time.
First, he had to get hold of some RaV. So he had his lab techs hold down a rabid dog while he sucked out some saliva from the jaws of this dog. Done. Next, he injected it into rabbits and dried out their spinal cords. There is a famous painting done of him doing this. After that, he figured that the virus was weakened enough to infect someone and have them not die while their immune system got to recognise it. He tested it on several dogs and thought that was good enough to start on little boys.
Nine year old Joseph Meister is commemorated forever in a statue outside the Institut Pasteur. He is forever known as that kid that got mauled by a rabid dog. Despite not being a doctor and could probably face a lawsuit that would screw him over forever, Pasteur injected this kid with ground-up, rabies-infected, rabbit spine. And it worked; the boy survived. 10 years later, Pasteur died, possibly from hyper-badass-aemia.
Joseph Meister ended up working as a caretaker for Pasteur’s tomb at the Institut Pasteur until his death. He died from an acute lead poisoning after shooting himself in the head with a revolver. He was 64.