RadioLab has an excellent short episode on one of the most morbidly fascinating of brain infections – rabies.

Rabies is a virus that can very quickly infect the brain. When it does, it causes typical symptoms of encephalitis (brain inflammation) – headache, sore neck, fever, delirium and breathing problems – and it is almost always fatal.

It also has some curious behavioural effects. It can make people hyper-reactive and can lead to uncontrolled muscle spasms due to its effect on the action coordination systems in the brain. With the pain and distress, some people can become aggressive.

This is known as the ‘furious’ stage and when we describe some as ‘rabid with anger’ it is a metaphor drawn from exactly this.

Rabies can also cause what is misleadingly called ‘hydrophobia’ or fear of water. You can see this in various videos that have been uploaded to YouTube that show rabies-infected patients trying to swallow and reacting quite badly.

But rabies doesn’t actually instil a fear of water in the infected person but instead causes dysphagia – difficulty with swallowing – due to the same disruption to the brain’s action control systems.

We tend to take swallowing for granted but it is actually one of our most complex actions and requires about 50 muscles to complete successfully.

Problems swallowing are not uncommon after brain injury (particularly after stroke) and speech and language therapists can spend a lot of their time on neurorehabilitation wards training people to reuse and re-coordinate their swallow to stop them choking on food.

As we know from waterboarding, choking can induce panic, and it’s not so much that rabies creates a fear of water, but a difficulty swallowing and hence experiences of choking. This makes the person want to avoid trying to swallow liquids.

Bathing, for example, wouldn’t trigger this aversion and that’s why rabies doesn’t really cause a ‘fear of water’ but more a ‘fear of choking on liquids due to impaired swallowing’.

The RadioLab episode discusses the case that launched the controversial Milwaukee protocol – a technique for treating rabies that involves putting you into a drug-induced coma to protect your brain until your body has produced the anti-rabies antibodies.

It’s a fascinating and compelling episode so well worth checking out.

UPDATE: This old medical film on YouTube goes through the stages of rabies infection. Warning: it’s a bit gruesome and has a melodramatic soundtrack but it is quite informative.

Link to RadioLab episode ‘Rodney Versus Death’.