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1- Atualização sobre a ocorrência de doenças de importância em Veterinária e em Saúde Pública em todo o mundo.
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Defesa Sanitária Animal (Legislação e Programas Sanitários do Ministério da Agricultura) e
demais assuntos relacionados à sanidade e Saúde Pública.
Este blog se destina a discutir a saúde animal dentro dos seus mais variados aspectos.
Good news, 20 years on, the BSE epidemic is finally over
by Roger Highfield7:00AM GMT 15 Feb 2011
The first hint of catastrophe came a quarter of a century ago. In October 1987, David Brown of The Sunday Telegraph described “a mystery brain disease [which] is killing Britain’s dairy cows and vets have no cure”. A few months later, he disclosed that the government had launched an inquiry into what was now being called bovine spongiform encephalopathy, or BSE. By the end of the decade, his stories were referring routinely to “mad cow disease”, and a chilling new phrase had entered the language.
The BSE epidemic cost us billions, and devastated the British farming industry. Now, that plague is at an end. A few days ago, in New Scientist, we described how just 17 cases were recorded worldwide in cattle last year.
Brown, who died in 2001, aged just 54, would have been surprised by the lack of publicity given to BSE’s demise. Overall, as many as three million animals were infected; in the peak year, 1992, the UK saw 37,280 diagnoses. Yet there are good reasons why any celebrations have been put on hold. All told, around half a million infected animals entered the food chain. Although it remains unclear how many people ate the most infectious parts, it is clear that the majority of the British population was exposed.
So far, the human equivalent of BSE, variant Creutzfeldt-Jakob disease (vCJD), has claimed 170 lives, mainly through consumption of BSE-infected beef. And because of the extraordinary incubation time of the disease, it is possible that many more cases may be waiting in the wings.
The story of BSE starts in the 1960s, with two London-based researchers – Tikvah Alper, of Hammersmith Hospital, and John Stanley Griffith, of Bedford College – who were studying scrapie, the equivalent disease in sheep. They suggested that such “spongiform” brain disorders were caused not by conventional agents such as viruses and bacteria, but a novel type of infectious agent: a rogue protein.
In a 1967 paper for Nature, Griffith assured readers that “there is no reason to fear that the existence of a protein agent would cause the whole theoretical structure of molecular biology to come tumbling down”. But to his peers, the idea was either heresy or simply idiocy.
The torch was carried forward by Stan Prusiner, a flamboyant American scientist, after one of his patients at the University of California, San Francisco, died of spongiform disease in 1972. After a decade of work, he came up with a snappy name for the rogue protein responsible: the “prion”, or “proteinaceous infectious particle”.
The whole idea, however, still challenged a central orthodoxy about the nature of the disease. Because of this, and the slender evidence base, a perception hardened that Prusiner’s big idea was closer to insanity than genius. “The personal attacks of the naysayers at times became very vicious,” he would later remark.
The prion theory was eventually vindicated – and Prusiner’s dogged labours rewarded with a Nobel prize – but scientists soon realised that these new particles operated on an extraordinarily long timescale. It takes years for prions to infiltrate the central nervous system, and years more for them to replicate and accumulate to levels that cause personality change, loss of body function and, eventually, death.
And although the current wave of vCJD is apparently fizzling out, after peaking in 2000 with 28 cases, there is a possibility that further waves may appear. We each inherit one of three different combinations of the two prion genes; so far, all the vCJD infections have been among of people with one particular combination, found in 37 per cent of the population. The rest of the population may be relatively immune; but it could be that the disease merely takes longer to develop. If so, the result would be two more waves of vCJD.
Prof John Collinge, of the Medical Research Council Prion Unit in London, has studied kuru, a related disease found in the Fore people of Papua New Guinea and spread by the now abandoned ritual of eating relatives’ brains at funerals. He says that these second and third waves might not appear for more than half a century – but fortunately, with the support of the National Prion Clinic, he has just announced the first accurate blood test for vCJD
The next step will be to test several thousand anonymous blood donors from a country unaffected by BSE, to make sure the test never gives a false positive for people who don’t have the disease. Then will come longer-term studies to assess what proportion of the population tests positive for prion infection (the current estimate is one in 4,000), and to assess how many carriers will then go on to develop the disease. Until that work is complete, and the uncertainty is ended, Britain will still live in the shadow of BSE.