Diseases that need new drugs: Need of the hour
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global burden of infections. Studies of these emerging infections reveal the evolutionary properties of pathogens and the dynamic relationships between microbes, their hosts and environment (Morens et al., 2004). The infections that have newly appeared in a population or existed previously and now rapidly increasing in incidence or geographic range is called emerging infection (EI). Acquired immune deficiency syndrome (AIDS) caused by human immune deficiency virus (HIV) was first recognized in 1981, and as a global killer HIV/AIDS now threatens to surpass the Black Death of the 14th century and the 1918-1920 influenza pandemic, each of which killed nearly 50 million people. Of the 'newly emerging' and 're-emerging/resurging' diseases after HIV/AIDS, the monkeypox, severe acute respiratory syndrome (SARS) in 2003, bird flu in 2006 and swine flu in 2009 had a worldwide impact; while the 2001 anthrax bioterrorist attack in US was a 'deliberately emerging' diseases. Actually emergence results from dynamic interactions between rapidly evolving infectious agents and changes in environment and host behaviour that provide such agents a favourable ecological niche (Morens et al., 2004). It was estimated that infectious disease alone contribute about 15 million (>25% of 57 million) annual deaths worldwide, and an additional millions of deaths from past infections (like streptococcal rheumatic heart disease) and complications with chronic infections, such as liver failure and hepatocellular carcinoma in people with hepatitis B or C (WHO Report 2004). The burden of morbidity (ill health) and mortality in infectious diseases is more in developing countries (Guerrant & Blackwood, 1999), particularly on infants and children (about 3 million children die each year from malaria and diarrhoeal diseases); while in developed nations mortality in infectious disease disproportionately affects indigenous and disadvantaged minorities (Butler et al., 2001).
Old microbes cause new diseases and the newly emerging infections Some infections once caused familiar diseases, but now causing new or uncommon diseases as found with Streptococcus pyogenes (caused a fatal pandemic of scarlet and puerperal fevers between 1830 and 1900) is now rare (Katz & Morens, 1992), and replaced by streptococcal toxic shock syndrome, necrotizing fasciitis and re-emergent rheumatic fever (Musser & Krause, 1998). Sometimes the diseases causing ability of a new microbe are delayed, as found with Koch-Weeks bacillus discovered by Robert Koch in 1883. More than a century later, a virulent clonal variant of Koch-Weeks bacillus or Haemophilus influenzae biogroup aegyptius was found to be responsible for Brazilian purpuric fever, a fatal emerging infection (Musser & Selander, 1990). Although the basis of emergences and severity of S. pyogenes and H. influenzae biogroup aegyptius are not fully known, but complex microbial genetic events are suspected. PCR