Breaking Transmission with Vaccines: The Case of Tuberculosis.

Abstract

Members of the Mycobacterium tuberculosis complex (MTBC) have evolved causing tuberculosis (TB) in different mammalian hosts. MTBC ecotypes have adapted to diverse animal species, with M. bovis being the most common cause of TB in livestock. Cattle-to-human transmission of M. bovis through ingestion of raw milk was common before introduction of the pasteurization process. TB in humans is mainly caused by M. tuberculosis. This bacterium is considered a genetically clonal pathogen that has coevolved with humans due to its ability to manipulate and subvert the immune response. TB is a major public health problem due to airborne person-to-person transmission of M. tuberculosis. The essential yet unanswered question on the natural history of TB is when M. tuberculosis decides to establish latent infection in the host (resambling the lysogenic cycle of lambda phage) or to cause pulmonary disease (comparable to the lytic cycle of lambda phage). In this latter case, M. tuberculosis kills the host with the aim of achieving transmission to new hosts. Combating the TB epidemic requires stopping transmission. M. bovis BCG, the present vaccine against TB, is derived from M. bovis and only protects against disseminated forms of TB. Thus, a priority in TB research is development of new effective vaccines to prevent pulmonary disease. Attenuated vaccines based on M. tuberculosis as MTBVAC are potential candidates that could contribute to break the TB transmission cycle.