Mechanisms of viral emergence

Domingo, Esteban

The second level of complexity results from a network of environmental, ecologic, and sociologic influences that affect the probability that a potentially pathogenic virus comes into contact with a new host. A good number of such influences are subjected to indetermination. To give a specific example, a change in temperature and humidity in a large geographical area may alter flora and fauna, and, as a result, the distribution of viral vectors (arthropods, birds, mammals). However, which vectors and how they will be affected by weather or climate conditions are usually difficult to predict since they depend on sets of ecological interactions. Finally, another level of complexity intervenes in the epidemiological outcome of a viral disease, once it has emerged. Severe acute respiratory syndrome (SARS) faded months after its emergence, while Acquired Immune Deficiency Syndrome (AIDS) has become a severe pandemics, to last for many decades or forever. The difference can be attributed to the pattern of virus-host interaction and the capacity of the virus to be transmitted from an infected host individual into a susceptible individual. Again, these processes fall into the domain of biological complexity. Advances in molecular virology and the development of computational tools for viral surveillance have greatly improved our knowledge of the factors that underlie the emergence and re-emergence of viral disease, and, interestingly and paradoxically, we understand some of the reasons behind the unpredictability of emergences.