Latent infection and active disease are fairly accepted concepts among TB clinicians. There is, however, an increasing understanding that the difference between these two states is less of a flipped switch between latent and active but rather a complex interaction between human and microbe that starts at the moment of exposure, stabilizes with quiescent immune control and then, in a subset of patients, progresses – first with an increasing but asymptomatic mycobacterial burden in the pulmonary parenchyma and then into a full blown classic clinical syndrome.
Two papers recently published in Nature suggest the spectrum of the host/pathogen interaction may not be so neatly divided (link below). Both use PET/CT imaging to study the progression of inflammation in the lungs of patients with various stages of TB. Most fascinatingly, one of the studies shows evidence that active lesions are still present at the end of six months of first-line therapy for active TB disease, raising the possibility that immune control is more important for successful treatment than traditionally appreciated.
Link leads to: http://www.nature.com/nm/journal/v22/n10/full/nm.4186.html