Why rabies still remains a killer virus
A VIRUS that infects your brain, makes you want to bite things, and is almost always fatal after symptoms appear probably sounds like something from a zombie movie. But this has been the modus operandi of rabies at least since 2300 BC, when it was described in the Eshuma Code of Babylon. The word’s Sanskrit etymology – rabhas, meaning “to do violence” – dates back even further, to 3000 BC.
In principle, no human in this day and age should die from rabies, and yet, according to a 2015 study, the virus kills 59,000 people annually. That’s 160 people every day, and the actual number might be far higher if we could count unreported or untreated cases. Most of these deaths occur in Asia and Africa, with India alone accounting for one-third of the world’s total mortality from rabies.
That total is not as high as the death toll from tuberculosis, HIV/ AIDS, and malaria; but, unlike those diseases, every mammal appears to be susceptible to rabies. Dogs, the predominant host in most regions, can become infected from any rabid wild animal, and then infect humans. Dogs showing symptoms may bite a human, but they can also transmit the virus simply by licking if their saliva comes into contact with a scratch, damaged skin or mucosa.
The rabies virus hijacks the nervous system and actually manipulates neural processes to make its host move faster. Infected humans will eventually hallucinate, become aggressive, and even fear water in the advanced stages of the disease.
Once these symptoms appear, rabies has no known cure, and death is almost certain. Fortunately, unlike most vaccine-preventable diseases, rabies allows for post-exposure inoculation, because the time of infection is generally known by the victim – especially if they were bitten – and the disease’s incubation period is relatively long, ranging from days to years, but averaging three to eight weeks. Whether administered before or after exposure, the vaccine is the same, but the immunisation schedule and the dosage differ between the two scenarios.
French scientist Louis Pasteur formulated the first rabies vaccine in 1885, by injecting the virus into rabbits, waiting for it to kill them, and then drying the infected nerve tissues to weaken the virus to the point that it could be safely administered. Then he successfully tested it on a nine-year-old boy who had been bitten by a rabid dog. In today’s world, Pasteur would be thrown in jail for practicing as an unlicensed physician and not following proper clinicalpractice standards; but we can all be thankful for his discovery.
Today, rabies vaccines are grown in a lab using cell cultures. The virus is then rendered inactive, purified and administered by injection into the arm. The World Health Organization recommends pre-exposure vaccinations for anyone whose occupation or residence implies continual, frequent, or increased risk of encountering rabies. This applies to everyone in rabies-endemic countries; unfortunately, not everyone in these countries gets vaccinated.
The rabies vaccine is on the WHO List of Essential Medicines, and has an average wholesale price of US$11 per dose in the developing world, and as much as $250 per dose in the United States. Of course, because the alternative to post-exposure vaccination is death, the treatment is extremely cost-effective however one looks at it.
Smallpox, which is believed to have emerged even before rabies, has now been eradicated, and programs are currently under way to put an end to polio, Guinea worm disease and other infectious ailments. So why is rabies still prevalent?
One reason is that the virus is almost always transmitted by animals, rather than by other humans. To address this, we should be investing in pet vaccinations, reducing wild and stray animal populations, and enforcing strict quarantines on animals crossing national borders.
In developed countries, preventing rabies largely requires controlling and immunising wildlife populations, which has proved effective in Switzerland and Germany. In Latin American countries where bat rabies is a threat, bovine vaccines have been used, as have anticoagulants, to kill bats that feed off the blood of the treated cattle.
Ultimately, the world’s poorest regions still bear most of the rabies burden. Dogs are not widely vaccinated, as they are in developed countries; and even when they are, their populations turn over very rapidly. Within a year of a large-scale vaccination effort, a new population of unvaccinated dogs will be roaming the streets and increasing the chances of an outbreak.
Meanwhile, developing countries’ healthcare systems are already grappling with tuberculosis, HIV/AIDS, and malaria, and post-exposure prophylaxis supplies are limited. Barring real progress on these challenges, one of the world’s oldest known viruses will continue to afflict humans and animals alike.
– Project Syndicate
Melvin Sanicas, a public health physician and vaccinologist, is regional medical expert at Sanofi Pasteur, Asia, Japan, and the Pacific.