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This edited volume demonstrates how the latest developments in biogeography (for example in phylogenetics, macroecology, and geographic information systems) can be applied to studies in the evolutionary ecology of host-parasite interactions in order to integrate spatial patterns with ecological theory.

Infectious diseases have existed longer than us, as long as us, or are relatively newer than us. It may be the case that a disease has existed for many, many years but has only recently begun affecting humans. At the turn of the century the number of deaths caused by infections in the United States had been falling steadily but since the '80s has seen an increase. In the past 30 years alone 37 new pathogens have been identified as human disease threats and 12% of known human pathogens have been classified as either emerging or remerging. Whatever the story, there is currently a \"war\" on infectious diseases. This war is simply the systematic search for the microbial \"cause\" of each disease, followed by the development of antimicrobial therapies. The \"war\" on infectious diseases, however, must be revisited in order to develop a more realistic and detailed picture of the dynamic interactions among and between host organisms and their diverse populations of microbes. Only a fraction of these microbes are pathogens. Thus, in order to explore the crafting of a new metaphor for host-microbe relationships, and to consider how such a new perspective might inform and prioritize biomedical research, the Forum on Microbial Threats of the Institute of Medicine (IOM) convened the workshop, Ending the War Metaphor: The Changing Agenda for Unraveling the Host-Microbe Relationship on March 16-17, 2005. Workshop participants examined knowledge and approaches to learning about the bacterial inhabitants of the human gut, the best known host-microbe system, as well as findings from studies of microbial communities associated with other mammals, fish, plants, soil, and insects. The perspective adopted by this workshop is one that recognizes the breadth and diversity of host-microbe relationships beyond those relative few that result in overt disease. Included in this summary are the reports and papers of individuals participating in the Forum as well as the views of the editors.

Dickson D. Despommier's vivid, visceral account of the biology, behavior, and history of parasites follows the interplay between these fascinating life forms and human society over thousands of years. Despommier focuses on long-term host-parasite associations, which have evolved to avoid or even subvert the human immune system. Some parasites do great damage to their hosts, while others have signed a kind of \"peace treaty\" in exchange for their long lives within them. Many parasites also practice clever survival strategies that medical scientists hope to mimic as they search for treatments for Crohn's disease, food allergies, type 1 diabetes, organ transplantation, and other medical challenges. Despommier concentrates on particularly remarkable and often highly pathogenic organisms, describing their lifecycles and the mechanisms they use to avoid elimination. He details their attack and survival plans and the nature of the illnesses they cause in general terms, enabling readers of all backgrounds to steal a glimpse into the secret work of such effective invaders. He also points to the cultural contexts in which these parasites thrive and reviews the current treatments available to defeat them. Encouraging scientists to continue to study these organisms even if their threat is largely contained, Despommier shows how closer dissection of the substances parasites produce to alter our response to them could help unravel some of our most complex medical conundrums.

Among Biomphalaria glabrata/Schistosoma mansoni snail–trematode combinations, it appears that some parasites succeed whilst others fail to infect snails. Snails that become infected are termed susceptible hosts. Those which are not infected are traditionally determined as ‘resistant’. Here the concept of B. glabrata resistance to S. mansoni is re-examined in the light of additional observations. It is suggested that, in B. glabrata/S. mansoni, compatibility is tested independently for each individual miracidium and host, and that the success or failure of an infection does not depend on the snail susceptibility/resistance status, but on the ‘matched’ or ‘mismatched’ status of the host and parasite phenotypes.

Schistosoma japonicum is a parasitic flatworm that causes human schistosomiasis, which is a significant cause of morbidity in China and the Philippines. Here we present a draft genomic sequence for the worm. The genome provides a global insight into the molecular architecture and host interaction of this complex metazoan pathogen, revealing that it can exploit host nutrients, neuroendocrine hormones and signalling pathways for growth, development and maturation. Having a complex nervous system and a well-developed sensory system, S .  japonicum can accept stimulation of the corresponding ligands as a physiological response to different environments, such as fresh water or the tissues of its intermediate and mammalian hosts. Numerous proteases, including cercarial elastase, are implicated in mammalian skin penetration and haemoglobin degradation. The genomic information will serve as a valuable platform to facilitate development of new interventions for schistosomiasis control. Schistosome genomics Two international consortia this week report the whole genome sequences of the blood flukes Schistosoma mansoni and Schistosoma japonicum , two of the three major pathogens that cause schistosomiasis, also called bilharzia. Schistosomiasis is a 'neglected' tropical disease affecting more than 200 million people in 76 countries. Analyses of the new genome sequences provide insights into the molecular architecture and host interactions of these pathogens, as well as avenues for future development of targeted interventions for this disease. These are the first two flatworm genomes to be sequenced, so they offer new angles on the early events in animal evolution, in particular the determination of body pattern and the development of tissues into organs. Schistosoma mansoni and Schistosoma japonicum are the pathogenic agents that cause the tropical disease schistosomiasis. Here, and in an accompanying paper, the genomes of these two flatworms are sequenced and analysed. The results provide insights into the molecular architecture and host interactions of the flatworms, as well as avenues for future development of targeted interventions for schistosomiasis.

The inhabitants of the mammalian gut are not always relatively benign commensal bacteria but may also include larger and more parasitic organisms, such as worms and protozoa. At some level, all these organisms are capable of interacting with each other. We found that successful establishment of the chronically infecting parasitic nematode Trichuris muris in the large intestine of mice is dependent on microflora and coincident with modulation of the host immune response. By reducing the number of bacteria in the host animal, we significantly reduced the number of hatched T. muris eggs. Critical interactions between bacteria (microflora) and parasites (macrofauna) introduced a new dynamic to the intestinal niche, which has fundamental implications for our current concepts of intestinal homeostasis and regulation of immunity.

Observations on the origin and mature structure of the haustorium of the Western Australian Christmas tree (Nuytsia floribunda) corroborate and extend the findings of earlier workers. We show that the previously described sclerenchymatous ‘horn’ or ‘prong’ formed within the haustorium acts as a sickle-like cutting device which transversely severs the host root and then becomes lodged in haustorial collar tissue directly opposite to that where it originated. The cutting process is deduced to be rapid and the gland-like fluid filled structure in the haustorium is suggested to generate a hydrostatic force driving the device through the host root. The haustorial parenchyma cells at the tight junction between the endophytic part of the haustorium and the cut face of the host root develop balloon-like outgrowths which intrude into the lumina of severed xylem vessels of the host. Experiments feeding 0.05% (w/v) basic fuchsin to freshly cut ends of host root segments distal to terminally-attached mature haustoria demonstrate an apoplastic pathway from host xylem elements fractured at the interface into haustorial parenchyma, and thence through vascular tissue to the haustorium into the transpiring plant of Nuytsia. Application of labelled water (D2O) to uncut basal roots of potted plants ofAcacia acuminata parasitized by Nuytsia results in labelling of leafy shoots of parasite and host, indicative of haustorial uptake of water by Nuytsia from host root xylem in the intact association. Measurements of xylem water potentials of pot-cultured seedling Nuytsia associated with a range of hosts, or of mature trees of Nuytsia and partner woody hosts in the native habitat, demonstrate consistently more negative potentials in the parasite than host, suggesting that the parasite may regularly obtain xylem water through its haustorial apparatus.

Rapid progress is being made in elucidating the molecular mechanisms involved in invertebrate immunity. This search for molecules runs the risk of missing important phenomena. In vertebrates, acquired protection and pathogen-specific responses were demonstrated experimentally long before the mechanisms responsible were elucidated. Without analogous experiments, mechanism-driven work may not demonstrate the full richness of invertebrate immunity.

Intraspecific variability of the cestode P. longicollis was studied in three host species: the Nelma ( Stenodus nelma ), the Lenok ( Brachymistax lenok ), and the Malma ( Salvelinus malma ) of the fish order Salmoniformes. Host forms of helminths were found to be similar in the intrapopulation diversity and in the proportion of rare forms evaluated by polymorphous features of the scolex shape and sexually mature segments. Host differences in morphophysiological traits such as the attachment, trophics, and reproduction have been revealed. The parasites from Nelma are shown to be the most diverse phenotypically. These forms show the maximum heterogeneity of diversity and distribution frequencies. The conclusion is drawn that the helminths respond to changes in the habitat conditions in the host predominantly by plastic traits.