[The worldwide challenges of "new" or reemerging communicable diseases at the dawn of the 21st century].

In the first part of this review, AIDS, prion diseases, Hantavirus and arbovirus infections, Ebola hemorrhagic fever, legionellosis, hepatitis C, enterotoxigenic Escherichia coli infections, Lyme disease, tuberculosis have provided alarming examples of emerging or reemerging infectious diseases. In this second part, the stress is placed on the reemergence of diphtheria and of serious streptococcal infections, on bartonelloses, Chlamydia infections, fungal infections, while malaria and cholera are still prevalent in several areas. The increasing resistance of too many pathogens to antimicrobial agents is a major source of concern, directly related to the challenge of nosocomial infections. An infectious cause has been demonstrated (or strongly suspected) for various diseases and the scope of infectiology keeps widening, while the threat of bioterrorism cannot be neglected. The causes of the emergence or reemergence of infectious diseases are multiple and diverse, often in direct relation with human activities (population migrations, changes in husbandry or farming practices, worldwide exchanges of goods and foods, inadequate uses of antibiotics) but also with climatic variations in several areas. The challenge represented by this unexpected comeback of infections to the forefront of human and animal pathology can only be met with a significant improvement of hygienic practices, cessation of certain dangerous behaviors and also, of course, with the development of novel antimicrobial molecules (acting on original targets) as well as of a whole series of new specific vaccines.