virus
Some of the present emerging diseases are not actually new, but are diseases that were catastrophic in the past Figure 22.23 . They devastated populations and became dormant for a while, just to come back, sometimes more virulent than before, as was the case with bubonic plague. Other diseases, like tuberculosis, were never eradicated but were under control in some regions of the world until coming back, mostly in urban centers with high concentrations of immunocompromised people. The WHO has identified certain diseases whose worldwide re-emergence should be monitored. Among these are two viral diseases dengue fever and yellow fever , and three bacterial diseases diphtheria, cholera, and bubonic plague . The war against infectious diseases has no foreseeable end.