Pestilence in the 21st century: Are diseases moving out of control, and how does an ecological education advance human health?
Evidence is growing that human changes to the environment are affecting the spread of pathogens like never before, and that an ecological understanding of infectious diseases is vital to advance human health. Recent outbreaks caused by agents such as Ebola virus, Chikungunya virus, and Nipah virus underscore the role of ecology and the environment in creating opportunities for pathogens to cross host species barriers or expand in numbers or geographic range. In the 1960s and 70s, the world appeared to be at a turning point where human infectious diseases were receding, but since that time, a number of new microbes appeared in human populations globally. At the same time, new pathogens have caused die-offs in livestock, agricultural crops, and a growing list of species across terrestrial, freshwater and marine ecosystems. These co-occurring outbreaks suggest that similar processes could be causing diseases to appear and spread in human and natural systems, and signal that human health and ecosystem health are intertwined. Ecological approaches can shed light on several questions vital to human health, such as why are new outbreaks or pathogen expansions happening now, and what types of populations or ecosystems are at highest risk? Understanding infectious diseases in the context of ecological systems can also lead to novel approaches for preventing pathogen exposure and spread, and ecological training could be especially useful to those seeking careers in medicine and public health policy.
From an ecological perspective, three of the most important drivers of new pathogen appearance and spread are habitat destruction, increased trade and travel, and global climate change. In terms of habitat loss, humans are altering ecosystems on this planet like never before, bringing people into more frequent and closer contact with new pathogens. Global connectedness in the form of trade and travel has increased the speed and ease with which humans move and transport materials around the globe, introducing pathogens into novel landscapes, and allowing pathogens to spread farther and faster. Global temperatures have increased during the past 50 years, and several classes of pathogens, including diarrheal diseases, vector-borne diseases and parasitic worms are especially sensitive to temperature and rainfall; shifts or expansion in latitude or altitude have already been recorded for several human pathogens and for crop diseases. Finally, several case studies demonstrate how ecological knowledge of pathogen transmission can lead to effective strategies to prevent or control cross-species transmission and limit future outbreaks.