A global perspective on the influence of environmental exposures on the nervous system

Abstract

Economic transitions in the era of globalization warrant a fresh look at the neurological risks associated with environmental change. These are driven by industrial expansion, transfer and mobility of goods, climate change and population growth. In these contexts, risk of infectious and non-infectious diseases are shared across geographical boundaries. In low- and middle-income countries, the risk of environmentally mediated brain disease is augmented several fold by lack of infrastructure, poor health and safety regulations, and limited measures for environmental protection. Neurological disorders may occur as a result of direct exposure to chemical and/or non-chemical stressors, including but not limited to, ultrafine particulate matters. Individual susceptibilities to exposure-related diseases are modified by genetic, epigenetic and metagenomic factors. The existence of several uniquely exposed populations, including those in the areas surrounding the Niger Delta or north western Amazon oil operations; those working in poorly regulated environments, such as artisanal mining industries; or those, mostly in sub-Saharan Africa, relying on cassava as a staple food, offers invaluable opportunities to advance the current understanding of brain responses to environmental challenges. Increased awareness of the brain disorders that are prevalent in low- and middle-income countries and investments in capacity for further environmental health-related research are positive steps towards improving human health.

Figure 1

Environmental (chemical and non-chemical) threats to brain health in low- and middle-income countries. Multiple sources of exposure (air, water and food) coexist, and malnutrition and vector-borne diseases, notably infections, compound the risk of brain disease. Co-exposures not shown include heat, psychological stress and a poor physical environment, such as crowding.

Figure 2

Environmental framework and pathways to environmentally induced neurological disease in low- and middle-income countries. Susceptibility to neurological disease is determined at the interface between a particular exposure, epigenetic and metagenetic make up, and the presence of co-morbidities.

Figure 3

Neurocognition deficits in konzo, a disease linked to eating cyanogenic cassava. a, Spasticity in a 14-year old boy severely affected by konzo. b, Deficits in mental processing are evident from the results of a neuropsychological test.