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What Happens When a Human Gets Rabies?

August 21, 2019


People have been scared of rabies for thousands
of years, many times depicting their fear in drawings and carvings of menacing dogs. But rabies is scary for more reasons than
just a painful bite. Because once the virus is inside us, it not
only destroys our body, but damages our mind, and it can happen fast, or lay dormant for
years before fatally attacking. So how exactly do we get from a dog bite to
a complete behavioral change to…death? The virus that causes rabies is spread through
saliva, so the most common way to contract rabies is through an animal bite, most likely from
a dog, bat, raccoon, skunk or fox. There have been a few, rare cases of transmission
through infected organ donors and an even rarer instance of a lab accident, but for
the most part it comes down to a bite from a rabid animal. So even though it’s a virus that can infect
and kill humans, it’s studied considerably in veterinary labs. OK. I am Dr. Susan Moore. I’m the laboratory director of the rabies
laboratory at Kansas State University, part of the veterinary diagnostic lab within the
vet school here. We are the largest rabies serology laboratory
in the world. So the rabies virus is in the family lyssavirus, lyssa means rage really. So that kind of tells you what this group
of viruses are capable of. And what they’re capable of is causing a
very quick and painful death caused by the virus making its way into your brain. It’s a neurotropic virus. So that means it’s preferentially going
to infect neural tissue or neural cells. So when it gets injected into the skin or
the muscle, it’s not going to replicate all that well but all it needs to do is replicate
enough that it can get to that neuromuscular junction where that it can go from the muscle
cells into the central nervous system. Now, at this point you’d think your immune
system would kick in, recognize this dangerous intruder and destroy it. But, your immune system doesn’t see it. This is thought to be because the virus replicates
slowly in the muscle tissue, slow enough not to cause any alarm. This gives it a chance to reach the nervous
system, where it hitches a ride up to the brain and slips through the blood brain barrier. It’s behind this shield where the rabies
virus can flourish while still being able to hide from our immune system, because the
blood brain barrier evolved to keep dangerous or harmful things out. But sometimes that includes immune cells. In fact, if T cells do get past the blood
brain barrier, the rabies virus has evasion techniques where it actually kills the T cells
that are coming in. As the virus replicates in the brain, it starts
to mess with the brain’s cellular proteins, causing neural dysfunction. This is where certain symptoms of rabies start
and how you can tell the infection has fully set in. Once the infection has fully set in, it will
start traveling back out through the nerves into innervated organs, hair follicles. But again, particularly through to the salivary
glands. So that it could be transmitted out. These neurological symptoms also help the
virus transfer to a new host. Hypersalivation ensures there is enough rabies-infected saliva in the optimal transmission location, your mouth. And hydrophobia, or
trouble swallowing, ensures that it stays there. In animals, the aggression can result in an
attack on another animal or a human. Put all three of those together and you have
a very effective way to ensure the rabies virus is passed on. Saliva is the way that rabies is transmitted. The way the virus is adapted, it is not in
blood. It’s not in body fluids. So it has to find a way to be transmitted
effectively, right, to perpetuate its existence. Now, this neurological damage caused by the
infection is the thing that finally tips off the immune system. However, at this point it’s too late. Even though your immune system is finally
going after the virus, it has already spread throughout the body. After that you have to remember this period
is pretty short. There’s just a couple days because then it’ll
progress into a coma and then death which is usually due to some kind of organ failure. But a bite from a rabid animal doesn’t always
mean certain death. People who have been exposed to the rabies
virus can get a series of shots that can boost the immune system and fight off the virus,
you just need to get to it before it reaches the brain. So surviving rabies is all about timing and
the location where you get bit. Where you get bit. It plays a big role. So since the virus has to travel through the
nerve system, the closer, and get to the brain, the closer that bite is to the brain, the
better for the virus. Bats are a danger for that reason
that it’s going to be biting probably around your head or your hands. But also you don’t
notice a bat bite because the teeth are so small and they are so small. Maybe. You have a bat on your shoulder and you don’t
know it. You just looked on your shoulder, didn’t you?

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