Emerging and re-emerging viruses in the era of globalisation.

Abstract

During their evolution, human beings, as every other animal and vegetable species, have had to face innumerable challenges from the world of micro-organisms. Indeed, the history of mankind is littered with ‘scourges’, that is, epidemics and pandemics characterised by high rates of morbidity and mortality. There have been numerous examples of major epidemics in the past centuries. In the Middle Ages Yersinia pestis was the cause of the Black Death, a plague that devastated the countries of the Mediterranean basin reaching as far as China1,2. in the 1500s after the colonisation of the New World by Europeans, epidemics of smallpox and measles contributed to the decline of the Aztecs1,3. In exchange for having spread such epidemics, the European population was exposed to syphilis2. At the end of the 1800s there was a spread of tuberculosis or ‘industrial disease’, this name so-called because its emergence coincided with the beginning of industrialisation in the Western world. Finally, there was what has been defined as the mother of all pandemics, the Spanish ‘flu of 1918–19, which infected a third of the world’s population and was responsible for the death of about 40–50 million people4. Half way through the 20th century, after the end of the Second World War, the perception that infectious diseases were under control began to spread. This was due to a series of improvements in social factors and health care, to the cleansing of the environment and water and to the availability of ever more effective vaccines and antibiotics3,5. Indeed at the time it was said that “it is time to close the book on infectious diseases”, claiming that the battle against infectious diseases could finally be considered to have been won5,6. Unfortunately, this optimistic view was to be proven unfounded in the following years owing to the emergence of new infectious diseases and the re-emergence of old ones in the last decades of the century and the beginning of the new one3. According to the WHO (World Health Organization) , infectious diseases are still the second cause of death in the world (and the first in developing countries), being responsible for about 15 million deaths each year7. High mortality rates are found above all in countries with limited economic resources, countries in which AIDS, tuberculosis, malaria, acute respiratory infections and infantile diarrhoeal diseases represent the five so-called ‘big killers’6,7. In the latter 25–30 years various new pathogens causing newly emerging infections have been identified, while several diseases supposedly under control in many areas of the world, are reappearing (re-emerging/resurging diseases) and causing multiple epidemic outbreaks2. Furthermore, thanks to the selection of drug-resistant strains, diseases such as malaria and tuberculosis, have conspicuously reappeared among some populations3,5. Finally, this picture is completed by the so-called ‘deliberately emergent’ pathogens (for example, anthrax and smallpox), whose spread could be intentionally planned by humans through bioterrorism3.