Why ra­bies still re­mains a killer virus

The Myanmar Times - - News - MELVIN SANICAS news­room@mm­times.com

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.

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