Biomarkers that reflect immune activation or dysfunction will be important in the management of infectious diseases.

The human species has been under constant bombardment from pathogens over thousands of generations. It is likely that this host–pathogen interaction has to some extent shaped the biology and genetics of both populations. Today, this battle is ongoing with a range of infectious pathogens worldwide, some recurring and others newly transmitted to humans from other species. The social and economic cost of infectious diseases is enormous, as reflected by a recent WHO report that lists infectious diseases as one of the main causes of mortality and morbidity among children and adults in developing countries [101]. Unfortunately, individuals in these regions are often exposed to multiple pathogens, potentially exacerbating disease progression or increasing the complexity of clinical presentation. The diagnosis and treatment of infectious diseases in developing countries has been difficult owing to conflict, poor sanitation and nutrition, and lack or limited access to preventive care and treatment (including immunization). However, the management of infectious diseases in developed countries also places a significant burden on the health system. Accordingly, there is a continuous need for tests that utilize biomarkers – measurable indicators of biological processes – that can provide rapid and cost-effective tools for the diagnosis of circulating infectious diseases and stratify individuals at risk of disease. Ideally, these methods can also be made available for point-of-care testing in some regions.