Global trends in emerging infectious diseases

Emerging infectious diseases (EIDs) are a significant burden on global economies and public health. Their emergence is thought to be driven largely by socio-economic, environmental and ecological factors, but no comparative study has explicitly analysed these linkages to understand global temporal and spatial patterns of EIDs. Here we analyse a database of 335 EID 'events' (origins of EIDs) between 1940 and 2004, and demonstrate non-random global patterns. EID events have risen significantly over time after controlling for reporting bias, with their peak incidence (in the 1980s) concomitant with the HIV pandemic. EID events are dominated by zoonoses (60.3% of EIDs): the majority of these (71.8%) originate in wildlife (for example, severe acute respiratory virus, Ebola virus), and are increasing significantly over time. We find that 54.3% of EID events are caused by bacteria or rickettsia, reflecting a large number of drug-resistant microbes in our database. Our results confirm that EID origins are significantly correlated with socio-economic, environmental and ecological factors, and provide a basis for identifying regions where new EIDs are most likely to originate (emerging disease 'hotspots'). They also reveal a substantial risk of wildlife zoonotic and vector-borne EIDs originating at lower latitudes where reporting effort is low. We conclude that global resources to counter disease emergence are poorly allocated, with the majority of the scientific and surveillance effort focused on countries from where the next important EID is least likely to originate.     

Recognition of cluster of differentiation 1 antigens by human CD4-CD8-cytolytic T lymphocytes

Human cluster-of-differentiation 1 (CD1) is a family of cell surface glycoproteins of unknown function expressed on immature thymocytes, epidermal Langerhans cells and a subset of B lymphocytes. Three homologous proteins, CD1a, b and c, have been defined serologically, and the CD1 gene locus on human chromosome 1 contains five potential CD1 genes. Analysis of the predicted amino-acid sequences of CD1 molecules reveals a low but significant level of homology to major histocompatibility complex (MHC) class I and class II molecules, and, like MHC class I molecules, CD1 molecules are associated non-covalently with beta 2-microglobulin. These structural similarities to known antigen-presenting molecules, together with the expression of CD1 on cells capable of antigen presentation, suggest a role for CD1 molecules in antigen recognition by T cells. Here we demonstrate the specific recognition of CD1a by a CD4-CD8- alpha beta T-cell receptor (TCR) expressing cytolytic T lymphocyte (CTL) line and the specific recognition of CD1c by a CD4-CD8- gamma delta TCR CTL line. The interaction of CD1-specific CTLs with CD1+ target cells appeared to involve the CD3-TCR complex, and did not show evidence of MHC restriction. These results suggest that for a subset of T cells, CD1 molecules serve a function analogous to that of MHC class I and II molecules.     

Drought sensitivity shapes species distribution patterns in tropical forests

Although patterns of tree species distributions along environmental gradients have been amply documented in tropical forests, mechanisms causing these patterns are seldom known. Efforts to evaluate proposed mechanisms have been hampered by a lack of comparative data on species' reactions to relevant axes of environmental variation. Here we show that differential drought sensitivity shapes plant distributions in tropical forests at both regional and local scales. Our analyses are based on experimental field assessments of drought sensitivity of 48 species of trees and shrubs, and on their local and regional distributions within a network of 122 inventory sites spanning a rainfall gradient across the Isthmus of Panama. Our results suggest that niche differentiation with respect to soil water availability is a direct determinant of both local- and regional-scale distributions of tropical trees. Changes in soil moisture availability caused by global climate change and forest fragmentation are therefore likely to alter tropical species distributions, community composition and diversity.