What is rabies, and why is it almost always fatal once symptoms begin?

The death of a young boy in Canada from rabies, after his family reportedly found a bat on his face, is the kind of case that shocks precisely because it is so rare in a high-income country. According to the Guardian, the child fell ill and died despite living in a place where the disease is almost never seen in people. The tragedy has drawn attention back to one of medicine's most unforgiving illnesses.

Rabies is a viral infection that attacks the nervous system. It is usually transmitted through the saliva of an infected animal, most often via a bite, though contact with a scratch or with mucous membranes can also carry risk. Worldwide, dogs are responsible for the majority of human cases, but in North America and Europe, where dog rabies has been largely controlled, bats are a leading source.

The most sobering feature of rabies is its progression. After exposure, the virus can incubate silently for weeks or even months as it travels along nerves toward the brain. During this window a person typically feels fine. But once the virus reaches the central nervous system and symptoms appear, the disease is almost invariably fatal. Survival after the onset of symptoms is extraordinarily rare.

Early symptoms can be vague, including fever, headache and discomfort or tingling at the site of exposure. As the infection advances it can cause agitation, confusion, difficulty swallowing, a fear of water known as hydrophobia, and eventually paralysis and death. There is no reliable cure once this stage begins, which is why prevention is everything.

The crucial point is that rabies is preventable. Prompt treatment after exposure, known as post-exposure prophylaxis, is highly effective. It involves thorough wound cleaning and a series of vaccine doses, sometimes combined with an injection of rabies antibodies. Administered before symptoms appear, this treatment stops the virus from ever reaching the brain.

The danger with bats is that their bites and scratches can be tiny and easy to miss. A person may not realise they have been exposed, particularly if a bat is found in a bedroom or near a sleeping child. Public-health guidance in many countries advises treating any potential bat contact seriously and seeking medical advice, even when no obvious wound is visible.

Experts stress that the appropriate response to a possible exposure is not panic but prompt action. Anyone bitten or scratched by a wild or unknown animal, or who wakes to find a bat in the room, is generally advised to wash the area and contact health services quickly so that the need for preventive treatment can be assessed.

The global burden of rabies remains significant, with tens of thousands of deaths each year, overwhelmingly in parts of Asia and Africa where access to vaccines and animal-control programmes is limited. Children are especially vulnerable because they are more likely to be bitten and less likely to report it. Vaccinating dogs has proven to be one of the most effective ways to reduce human cases.

Cases in countries like Canada are rare enough to make headlines, and that rarity is itself a public-health achievement, the product of animal vaccination, surveillance and access to treatment. But rare is not the same as impossible, and this death is a reminder that the virus has not disappeared.

The lesson health authorities draw from such cases is consistent: rabies is close to untreatable once it takes hold, but almost entirely avoidable before it does. The narrow window between exposure and the onset of symptoms is where lives are saved, which is why doctors urge people never to dismiss a possible bat encounter, however minor it may seem.