I'm wondering - if it is antraz, could the flesh samples tested in Belem be the cause of the confusion? That is, they've decomposed, that could effect the germs too? The first tests in Rio Trombetas - were they flesh? Something else too? They would be fresher in the flesh.
I recall that the tests in America after 9/11 were often of the spores attached to the spreading medium - taken from walls, computer key boards, swabs from nasal passages - free of the effects of flesh decomposition.