Health

TB vaccine protects before and after exposure

  24 January 2011 5:00am
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A new vaccine that can fight tuberculosis (TB) before and after infection has been developed by Danish scientists.It could offer protection for many years more than is now possible.TB is a huge global problem, particularly in developing countries, where access to antibiotics to treat the disease is limited.The latest vaccine, so far tested in animals, is featured in the journal Nature Medicine.TB is a disease of the lungs, causing symptoms such as coughing, chest pains and weight loss. Untreated, it can be deadly.However, only in a small number of cases - fewer than 5% - do the symptoms develop immediately after infection.In more than 90% of cases, once Mycobacterium tuberculosis, the bacterium which causes the disease, has invaded the body it changes its chemical signature, and lives in a dormant - or "latent" - state.Usually the bacterium never emerges from this latent state, but in around 10% of cases it reactivates - often years or even decades later - to trigger severe symptoms.Current vaccines, such as the BCG vaccine, work only if given before exposure to the bacterium.They do not prevent infection, but do prevent acute symptoms and disease from emerging.But once the bacterium has changed into its latent form it is effectively immune to the vaccine, and can bide its time, reactivating after the vaccine has ceased to have a preventative effect.If successful in human trials, the new vaccine would be able to tackle that problem.'Major breakthrough'Developed by a team at the Statens Serum Institute in Copenhagen, it combines proteins that trigger an immune response to both the active and latent forms of Mycobacterium.Researcher Professor Peter Lawætz Andersen said: "It might be possible to give a booster jab post-exposure to older children or even young adults which would protect them well into adulthood."Although TB can be treated with antibiotics, those drugs are often not easily accessible in the developing world, where the new vaccine could have the greatest benefit.Professor Andersen said: "In these areas you cannot go in and treat more than half the local population. For instance, in Capetown 60% of people are thought to be infected."Professor Peter Davies, secretary of the group TB Alert, said: "A vaccine which can both protect against initial infection and protect from a breakdown of infection into disease is a major breakthrough."One of the main disadvantages of BCG was that it could only prevent infection going on to disease in the initially uninfected individual. It was therefore of no use in protecting infected adults who would become an infectious source of disease. Protecting children, though of value, does not protect against transmission, as children with active disease do not usually transmit disease."So far so good but we must remember that mice are not men (or women)."Professor Francis Drobniewski, Director of the Health Protection Agency's National Mycobacterium Reference Laboratory said: "This is an exciting and thoughtful piece of research. The existing BCG vaccine is cheap, safe, widely used but of limited efficacy."With over nine million new TB cases globally each year and increasing levels of drug resistance new diagnostics, drugs and especially effective vaccines are desperately needed."UK situationThe number of tuberculosis cases in the UK topped 9,000 in 2009 - the highest for nearly 30 years.Diagnoses have been rising almost continuously since the 1980s, with many of the new cases thought to be among people who caught the disease abroad.There has also been a sharp rise in drug-resistant TB cases.The Health Protection Agency has warned more efforts must be made to curb the problem.Source: BBC

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