Rabies – does it have to be fatal?

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800px-Military_dog_barkingRabies is a reliable killer – the only known infection with a near 100% fatality rate. That is until 2004 when a pediatrician in Milwaukee, USA, tried an experimental protocol that saved the life of 15-year-old Jeanna Geise. Dr Willoughby’s treatment, published here, was to induce a coma to protect her brain from the disease, while waiting for her to develop antibodies that could fight the virus.

While in a coma, Jeanna was given anti-viral drugs ribavirin and amantadine, although neither of these is proven to be effective against rabies. She had been bitten by a bat over a month earlier, too late for post-exposure vaccination, but the novel treatment worked, making Jeanna the sixth documented person to ever survive rabies and the only to survive following a specific treatment regimen. The Milwaukee Protocol, as it is now known, has been effective in five more patients since 2004, out of more than forty attempts, according to a helpful database from the Medical College of Wisconsin.

Rabies incidence varies hugely from country to country – it is fairly common in the USA, but extremely rare in the UK, with only five human cases since 2000. All UK cases are imported, mostly from regions where the disease is endemic, such as a case in 2012 imported from India, published today in Virology Journal. The patient was bitten by a rabid dog, but received no treatment until she arrived at hospital in London, when she initially received the rabies vaccine, followed by the drugs prescribed by the Milwaukee Protocol.

Dogs are responsible for the vast majority of human infections, especially in India where encountering a rabid dog can be an all too common experience. Feral dogs number in the millions; consequently, of the 55,000 rabies cases annually, 20,000 occur there. Conversely, the UK is one of many countries certified as rabies-free, a distinction held since 1902, so every case is under careful scrutiny. Rabies can be spread in the saliva of numerous terrestrial carnivores – rabid cats are a growing problem in the USA, according to the CDC.

The most recent case in the UK was sadly fatal, despite treatment with the anti-excitatory and anti-viral drugs of the Milwaukee Protocol. Why does the protocol work in some cases, but not in others? This is difficult to answer, partly because of minor changes each time it is used. Interestingly, an emerging theory proposes that rabies may not, in fact, be 100% fatal. Uniform lethality is a distinction shared with no other virus, even smallpox and Ebola have their survivors. The situation is unclear, but a recent study claims to have found rabies survivors amongst those bitten by vampire bats in Peru.

This suggests an intriguing hypothesis – perhaps the Milwaukee Protocol only works in those that have certain immunological features. Some of us may have a natural ability to fight the virus, given the extra time that the protocol buys. Nevertheless, the safest bet if you’re exposed to a rabid animal is to seek an immediate dose of the vaccine, which has been saving lives since 1885. An estimated 40,000 Americans receive this post-exposure prophylaxis each year. Better still – avoid getting bitten.