Pathogen–host–environment interplay and disease emergence

Engering, Anneke; Hogerwerf, Lenny; Slingenbergh, Jan

Land-use changes and changes in climate and weather modulating host and vector habitats or environmental pathogen survival may drive a local range expansion of pathogens. 59, [96] [97] [98] An example is the expansion of the tick-borne pathogen B. burgdorferi sensu strictu, the cause of Lyme disease, in the USA, probably driven by a combination of changes in climate, agriculture and land use. 99 Geographic jumps typically result from international trade and travel, including transport of live animals, food items, plants and accompanying insects, thus enabling disease agents to hitchhike and establish in novel places. 59, 97, 100 For instance, a major epizootic of Rift Valley Fever virus in the Arabian Peninsula in 2000-2001 was attributed to shipments involving live animals and mosquitoes from mainland Africa. 101 Similarly, in 2003, the bacterium Ralstonia (Pseudomonas) solanacearum race 3 biovar 2 jumped from Kenya to greenhouses in the USA via imported geranium plants. 77 The globalization of fisheries production and supply explains how white spot disease in shrimps became first introduced in Mozambique from Asia in 2011. Geographic jumps may also result from the active migration of wild species including a range of mammals and also birds, fish and arthropods, in the process introducing entire microbial reservoirs into novel geographic areas. 46 CONCLUDING REMARKS AND PERSPECTIVES Pathogens will continue to find ways to exploit novel host resources, be it humans, domestic animals, plants, marine life or natural ecosystems. 102 The framework presented here comprehensively categorizes the great diversity of EID agents and events on the basis of the changes in the interplay between pathogens, hosts and environment. EID events are grouped into three main, distinct and only slightly intersecting categories that each features typical disease ecological An infectious disease emergence framework A Engering et al 5 dynamics, sets of drivers of emergence and pathogen trait profiles. The framework is not restricted to infectious disease emergence in human and livestock as it would also apply to pest and disease challenges emerging in plant production, fisheries and bee keeping. The framework thus has potential to assist in disentangling and structuring a formidable amount of information on infectious diseases and may be used to help identify the circumstances in food and agriculture, natural resource management and other forms of human behavior that enhance pathogen emergence. This, in turn, may lead to adjustments in food and agriculture, land use, physical planning, trade practices and so on, based on more thorough understanding of the interplay and feedback between human action, pathogen-hostenvironment dynamics, and pathogen evolution. Certain extremely flexible pathogens fit several emergence categories. For example, influenza A viruses collectively have shown capable of species jumps, virulence jumps, and inter-continental scale invasions. H5N1 HPAI emerged as a virulence jumper in avian hosts in 1996, paving the way for a presumably migratory waterfowl vectored panzootic of the H5N1 subclade 2.2 viruses in 2006, and at the same time, led to continual spill-over and even rare events of humanto-human transmission, posing the threat of a species jump. In addition, the build-up of influenza A virus genetic diversity in the humanswine-avian host reservoir continues to increase.