Zoonotic, arthropod-borne pathogens currently encompass some of the most important emerging infectious diseases of humans. Mosquito-borne and tick-borne diseases have gained notoriety for increased incidence in the human population, geographic expansion, potentially novel clinical manifestations, and emergence into novel vectors and hosts. Surrounding these changes are global shifts in land cover and climate, known drivers of vector-borne disease spillover and emergence; however, specific mechanisms remain understudied for many pathogens. Spillover of zoonotic pathogens is expected to be acute in areas of high host and vector diversity and rapid land conversion, specifically in tropical forests. Hypotheses for the impact of land cover change on pathogen emergence focus primarily on host and vector abundance, diversity, and their interactions. Agricultural expansion is a key contributor to deforestation in these areas. Insertion of agricultural matrices into tropical forests alters vector and host community composition while increasing the proximity of vector, hosts, and humans and the potential for viral spillover. The relationships between agriculture insertion into forests and spillover of arboviruses in the family Flaviviridae will be discussed; primarily field-based research utilizing vector sampling and bloodmeal identification to characterize host networks in shifting landscapes.
Results/Conclusions
Conversion of rainforest to agriculture decreases species richness overall; although, this reduction varies by crop matrix, where mixed matrix crops have a smaller effect than monocultures. While the dilution of host species diversity is highly studied in human-altered landscapes, vector species richness is also impacted. Insertion of agricultural crops commonly dilutes mosquito diversity to a relatively high abundance of flavivirus vectors. As expected, host utilization detected via bloodmeal identification of mosquitoes narrows to primarily anthropophilic hosts along a gradient from intact forest to urban land cover types. For many flaviviruses with zoonotic transmission cycles, this phenomenon indicates that initial spillover is likely to occur in forests where hosts and vectors remain diverse and abundant. Emergence into human transmission cycles occurs when infected individuals enter populated areas where competent vectors are abundant, such as urban landscapes. People consistently use forests for a number of resources including; plant harvesting, human travel, hunting, and poaching. The relationship of these activities to flavivirus transmission remain unknown but are speculated to enhance viral spillover. Importantly, agriculture insertion commonly provides access to forests and likely contributes to an increased frequency of interactions between vectors, hosts, and humans facilitating arboviral spillover.