Non-specific effects of BCG in protozoal infections: tegumentary leishmaniasis and malaria.

BACKGROUND: Leishmaniasis and malaria are major causes of illness in the poorest countries. In the absence of efficient strategies to prevent infections and to control the transmission of the parasites by insect vectors, treatment relies on drug therapy. Vaccine development continues on several fronts; however none of the candidates developed has so far been shown to provide long-lasting protection at a population level. Because the bacillus Calmette-Guérin (BCG) vaccine can induce heterologous protective effects, we hypothesize that BCG has beneficial effects in the control of tegumentary leishmaniasis (TL) and malaria. AIMS: In this review we describe evidence for the protective efficacy of BCG against tegumentary leishmaniasis and malaria in humans. SOURCES: Relevant data from peer-reviewed scientific literature published on Pubmed up to January 2019 were examined. CONTENT: From experimental animal and various human studies with BCG and one recent randomized malaria trial there is evidence that BCG has beneficial effects in Leishmania spp. and Plasmodium falciparum infections. Although the precise mechanisms remain unknown, BCG can activate innate immune responses, and an increasing body of evidence demonstrates that the induction of trained innate immunity could explain its non-specific protective effects. IMPLICATIONS: Despite many years of research to prevent and treat TL and malaria, these diseases remain a public health problem in tropical countries. Future studies are required to examine if BCG vaccination could be used as an effective treatment option.