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CHAPTER 1 AN INTRODUCTION<br/>TO PARASITISM<br/>1.1 BUILDING AN UNDERSTANDING<br/>OF THE BASICS OF PARASITISM<br/>Parasites live in or on their hosts and cause<br/>them harm<br/>Opinions vary on how to define some of the key<br/>aspects of parasites and their biology<br/>The residence time for a parasite in or on a host<br/>is highly variable<br/>There are many additional ways to categorize parasites<br/>1.2 HOSTS—ESSENTIAL LIFELINES FOR<br/>PARASITES<br/>Hosts also fall into several different categories<br/>1.3 APPRECIATING PARASITISM'S PLACE<br/>IN NATURE<br/>Parasitism is one of several categories of symbiotic<br/>associations<br/>Parasitoids straddle the boundary between<br/>predation and parasitism<br/>Our understanding of parasitism is enhanced by<br/>an appreciation of its relationship to another<br/>ubiquitous type of symbiosis, mutualism<br/>REVIEW QUESTIONS<br/>REFERENCES<br/>CHAPTER 2 AN OVERVIEW OF<br/>PARASITE DIVERSITY<br/>2.1 THE DIVERSITY OF PARASITE SPECIES<br/>What constitutes a parasite species requires some<br/>explanation<br/>Given these considerations, how many species of<br/>parasites inhabit the Earth?<br/>Evolutionary trees are used to visualize evolutionary<br/>relationships and to display parasite diversity<br/>Efforts are well underway to reveal the overall<br/>tree of life<br/>Horizontal gene transfer (HOT) has been pervasive<br/>throughout the evolution of life<br/>Many bacteria are parasites<br/>Eukaryotes are a very diverse group that includes<br/>many different kinds of parasites<br/>HOT has also played a role in the evolution of<br/>eukaryotic parasites<br/>The Apicomplexa is a huge, important, nearly<br/>exclusive parasitic group of organisms<br/>Many well-known parasites belong to familiar<br/>groups of multicellular organisms<br/>2.2 INSIGHTS INTO PARASITISM FROM<br/>THE STUDY OF DIVERSITY<br/>The phylogenetic affinities of enigmatic parasites<br/>can be revealed<br/>Some groups of parasites remain "persistent<br/>problematica"<br/>Studies of parasite diversity reveal how particular<br/>parasites came to infect humans<br/>Studies of diversity can help reconstruct the<br/>historical biogeography of parasites<br/>2.3 THE ONGOING QUEST TO REVEAL<br/>AND UNDERSTAND PARASITE DIVERSITY<br/>DNA barcoding is one way to catalog parasite<br/>diversity<br/>Some parasites exist in complexes of cryptic species<br/>Whole lineages of unapparent parasites may escape<br/>our attention<br/>Metagenomics provides a new way to reveal parasite<br/>diversity<br/>Studies of parasite diversity help provide a better<br/>foundation for taxonomy<br/>2.4 OTHER WAYS TO CONSIDER<br/>PARASITE DIVERSITY<br/>Diversity within parasite species is extensive and<br/>important<br/>Do parasites give rise to free-living organisms?<br/>REVIEW QUESTIONS<br/>REFERENCES<br/>CHAPTERS THE PARASITE'S<br/>WAY OF LIFE<br/>3.1 A HISTORICAL PERSPECTIVE OF THE<br/>PARASITE LIFE CYCLE<br/>Early medical and natural history studies gave rise<br/>to an understanding of parasite life cycles<br/>Mosquito transmission was first demonstrated for<br/>filarial worms<br/>Arthropod transmission for filarial worms suggested<br/>that other diseases may be similarly transmitted<br/>3.2 AN OVERVIEW OF PARASITE LIFE<br/>CYCLES<br/>Parasites with direct life cycles use only a single host<br/>Two or more hosts are necessary for those parasites<br/>with indirect life cycles<br/>3.3 THE PARASITE'S TO DO LIST<br/>Effective transmission is essential for all parasites<br/>High reproductive rates are common in many<br/>parasite life cycles<br/>Both sexual and asexual reproduction are used by<br/>apicomplexans such as Toxoplasma gondii<br/>Parasites may use strategies other than high<br/>fecundity to achieve transmission<br/>Many factors can complicate an understanding of<br/>parasite transmission<br/>Mathematical models provide a useful tool to<br/>predict transmission rates<br/>Many parasites must migrate to specific sites or<br/>tissues within the host<br/>The evolution of complex migration within a host<br/>is not always clear<br/>Parasites are adapted to maintain their position on<br/>or within the host<br/>Finding a mate is a requirement for many sexually<br/>reproducing parasites<br/>Parasite genomes reflect their adaptations to a<br/>parasitic lifestyle<br/>The relationship between parasitism and genome<br/>size is not always clear<br/>Propagules are released through a portal of exit<br/>Parasites undergo complex developmental changes<br/>in response to environmental cues<br/>Epigenetic phenomena and co-opting of host<br/>signaling molecules may be important in parasite<br/>development<br/>REVIEW QUESTIONS<br/>REFERENCES<br/>CHAPTER 4 HOST DEFENSE<br/>AND PARASITE EVASION<br/>4.1 AN EVOLUTIONARY PERSPECTIVE<br/>ON ANTI-PARASITIC IMMUNE RESPONSES<br/>Prokaryotes have developed remarkable immune<br/>innovations during their billions of years<br/>encountering parasites<br/>Many kinds of parasites compromise the health of<br/>plants so it is important to know how plants defend<br/>themselves<br/>Although plants lack specialized immune cells, they<br/>still can mount effective, long-term responses to<br/>parasites<br/>Many nematode species are specialized to<br/>parasitize plants<br/>Invertebrates have distinctive and diverse innate<br/>immune systems<br/>Invertebrates, including vectors and intermediate<br/>hosts, mount immune responses to contend with<br/>their parasites<br/>Invertebrates also adopt distinctive behaviors to<br/>supplement their anti-parasite immune responses<br/>Parasites suppress, manipulate, and destroy<br/>invertebrate defense responses<br/>Some parasites rely on symbiotic partners to<br/>subvert the immune responses of their invertebrate<br/>hosts<br/>Some invertebrates enlist symbionts to aid in<br/>their defense<br/>Researchers hope to manipulate invertebrate<br/>immune systems to achieve parasite control<br/>4.2 AN OVERVIEW OF VERTEBRATE<br/>DEFENSE<br/>4.3 IMMUNE RESPONSES TO<br/>EUKARYOTIC PARASITES<br/>Recognition of PAMPS initiates the immune<br/>response to protozoa<br/>Immune responses to protozoa include both<br/>humoral and cell mediated components<br/>Protective immunity to malaria develops as a<br/>consequence of repeated exposure<br/>Immune responses are generated against each<br/>stage m the Plasmodium life cycle<br/>Helminth parasites provoke a strong Th-2<br/>response °<br/>Extensive changes to the intestinal epithelium<br/>occur m response to intestinal helminths<br/>Immunocompromised hosts are more vuln. rable<br/>to parasitic infection and increased patholo-y<br/>4.4 PARASITE EVASION OF HOST<br/>DEFENSES<br/>Many parasites are able to evade complementmediated<br/>innate<br/>immune<br/>responses<br/>Intracellular parasites have evolved mechanisms<br/>to avoid destruction by host cells<br/>Parasites may interfere with intracellular signaling<br/>pathways<br/>Some parasites interfere with antigen presentation,<br/>resulting in an impaired immune response<br/>Some parasites regularly change their surface<br/>antigens to avoid immune responses<br/>Parasites frequently suppress or alter host<br/>immune responses by interfering with cell<br/>communication<br/>Some parasites render themselves invisible to<br/>immune detection<br/>Various parasites are able to undermine the effector<br/>functions of antibodies<br/>REVIEW QUESTIONS<br/>REFERENCES<br/>CHAPTER 5 PARASITE VERSUS<br/>HOST: PATHOLOGY AND DISEASE<br/>5.1 PATHOLOGY RESULTING FROM<br/>PARASITIC INFECTIONS<br/>Parasites can induce pathogenesis in various ways<br/>Pathology can be categorized as one of several<br/>general types<br/>Parasites can cause direct trauma to host cells,<br/>tissues, and organs<br/>Mechanisms underlying the pathogenicity of<br/>Entamoeba histolytica remain obscure<br/>Parasitic infection can alter host-cell growth<br/>patterns<br/>Many parasites adversely affect host nutrition<br/>Plasmodium infections can result in host iron<br/>deficiency<br/>Toxins are a less frequent component of parasite<br/>pathology<br/>Pathology often results from immune-mediated<br/>damage to host cells and tissues<br/>Immunopathology is an important component of<br/>the pathology observed in malaria<br/>Granulomas formed in response to parasite antigen<br/>are both protective and pathological<br/>Parasites may serve as a trigger for autoimmunity<br/>Toxoplasma gondii may both contribute to and<br/>help to prevent artherosclerosis<br/>5.2 PARASITES AND HOST BEHAVIOR<br/>Some parasites may modify host behavior to<br/>facilitate transmission<br/>The mechanisms that parasites use to alter host<br/>behavior are obscure<br/>Infected hosts may display unusual neurotransmitter<br/>profiles in their central nervous systems<br/>5.3 PARASITE-MEDIATED AMELIORATION<br/>OF PATHOLOGY<br/>Parasitic infection may be required for proper<br/>immune system development<br/>Certain intestinal helminths may reduce the host<br/>inflammatory response<br/>Intestinal helminth infection results in activation<br/>of regulatory T cells<br/>Intestinal helminths can be administered<br/>therapeutically<br/>REVIEW QUESTIONS<br/>REFERENCES<br/>CHAPTERS THE ECOLOGY OF<br/>PARASITISM<br/>6.1 DEFINING THE HABITATS OF<br/>PARASITES<br/>Parasites occupy multiple habitats in succession<br/>Parasites have microhabitat preferences and occupy<br/>specific sites within their hosts<br/>Host specificity is one of parasitisms most distinctive<br/>properties<br/>Encounter and compatibility filters determine<br/>the range of host species used by a parasite<br/>The origins and consequences of host specificity are<br/>debated<br/>Underlying mechanisms dictating specificity are<br/>also often not known<br/>6.2 PARASITE POPULATION BIOLOGY<br/>Parasite populations are complex<br/>Parasites often show aggregated (ovei dispersed)<br/>distributions in their hosts<br/>Both density-independent and density-dependent<br/>factors influence parasite population size<br/>Intraspecific competition can regulate parasite<br/>populations in different ways<br/>Parasite population studies often require a long-term<br/>perspective and detailed sampling<br/>6.3 PARASITE COMMUNITIES<br/>The richness of parasite communities varies<br/>among host species for reasons that are still<br/>debated<br/>Most studies suggest parasite communities are<br/>stochastic in nature<br/>Parasite species within infracommunities engage<br/>in negative and positive interactions with one<br/>another<br/>Generalizable patterns are also elusive in<br/>component communities of parasites<br/>Human parasites have a distinctive community<br/>ecology<br/>6.4 THE ROLE OF PARASITES IN FOOD<br/>WEBS AND ECOSYSTEMS<br/>Parasites can be a food source for other organisms<br/>6.5 GLOBAL PAHERNS IN PARASITE<br/>DIVERSITY<br/>6.6 PARASITE EFFECTS ON HOST<br/>ECOLOGY<br/>Hosts try both to avoid infection and to actively<br/>remove parasites if they do become infected<br/>Hosts also change their diets and engage in<br/>self-medication when infected<br/>Parasites influence host migratory behavior<br/>Parasites can regulate host populations, but<br/>examples are few<br/>Parasites influence competitive interactions<br/>among hosts<br/>Parasites can manipulate their hosts to affect the<br/>likelihood of predation<br/>6.7 ECOLOGICAL IMMUNOLOGY<br/>6.8 THE METABOLIC THEORY OF<br/>ECOLOGY AND PARASITES<br/>6.9 EPIDEMIOLOGY AND ITS<br/>RELATIONSHIPS WITH ECOLOGY<br/>Modeling is an invaluable approach to the study<br/>of infectious diseases<br/>Microparasites exemplify basic modeling<br/>approaches that estimate population size and<br/>clarify transmission<br/>Models of macroparasite populations and<br/>transmission involve keeping track of individual<br/>parasites<br/>Models for parasites with complex life cycles<br/>involving vectors become more complex<br/>New models open the black box and estimate<br/>microparasite populations within hosts and the<br/>influences on them<br/>Models need to take spatial and temporal factors<br/>into account<br/>Some individual hosts may serve as<br/>superspreaders<br/>REVIEW QUESTIONS<br/>REFERENCES<br/>CHAPTER? EVOLUTIONARY<br/>BIOLOGY OF PARASITISM<br/>7.1 MICROEVOLUTION IN PARASITES<br/>The subdivided nature of their populations<br/>influences the evolution of parasites<br/>The effective population size, Ne, influences parasite<br/>evolution<br/>The mode of parasite reproduction affects<br/>microevolutionary change<br/>Stability of the host environment influences parasite<br/>microevolution<br/>The mobility of parasites impacts their evolution, as<br/>exemplified by bird lice<br/>Parasite microevolutionary change is strongly<br/>impacted by host mobility<br/>A parasites life cycle also affects the potential for<br/>evolutionary change<br/>7.2 COEVOLUTION OF PARASITE-HOST<br/>INTERACTIONS<br/>Parasites and hosts reciprocally affect each other's<br/>evolution<br/>Parasites and hosts engage in arms races<br/>In parasite-host relationships, there can be an<br/>advantage to being rare<br/>Parasites and hosts can be locally adapted, or<br/>maladapted, to one another<br/>Some factors conspire to limit strong<br/>coevolutionary dynamics between parasites<br/>and hosts<br/>7.3 THE EVOLUTION OF VIRULENCE<br/>Virulence and transmission biology of parasites<br/>are linked<br/>The trade-off hypothesis requires a nuanced<br/>approach<br/>The mode of transmission influences virulence<br/>7.4 MACROEVOLUTIONARY PARASITOLOGY<br/>New parasite species are potentially formed in at<br/>least three different ways<br/>Different outcomes can be expected when parasites<br/>or their hosts diversify<br/>What does the evidence suggest about how<br/>parasites have speciated?<br/>Does sympatric speciation occur in parasites?<br/>Host switches can enable radiations in parasites<br/>Parasites go extinct, sometimes along with their hosts<br/>Macroevolutionary patterns among parasites are<br/>not yet very clear<br/>7.5 SOME DISTINCTIVE ASPECTS OF<br/>PARASITE EVOLUTION<br/>Organisms have repeatedly adopted parasitism<br/>by more than one route<br/>Some parasites are derived from their hosts<br/>Selection can favor the evolution of complex<br/>parasite life cycles<br/>Sometimes complex life cycles are simplified<br/>secondarily<br/>Parasites often have simplified bodies or genomes<br/>but also have other talents not seen in free-living<br/>organisms<br/>7.6 PARASITE EFFECTS ON HOST<br/>EVOLUTION<br/>Parasites select for genetic changes and genetic<br/>diversity in their hosts<br/>Parasites affect the evolution of host MHC genes<br/>Parasites play a role in host selection of mates<br/>Host speciation may be facilitated by parasites<br/>Can infection directly cause speciation?<br/>Parasites are believed to favor the evolution of<br/>sexual reproduction in their hosts<br/>Parasites can cause extinction of host species<br/>REVIEW QUESTIONS<br/>REFERENCES<br/>CHAPTERS PARASITES AND<br/>CONSERVATION BIOLOGY<br/>8.1 SOME THEORY ABOUT PARASITES<br/>AND CONSERVATION BIOLOGY<br/>Theory often predicts parasites will not extirpate<br/>their hosts, but by no means always<br/>Persistent parasite infectious stages may also<br/>favor demise of host populations<br/>The presence of a parasite-tolerant host species<br/>may endanger a susceptible one<br/>8.2 PARASITES INFLUENCE EFFORTS TO<br/>PRESERVE HOSTS<br/>Parasites can cause extinction of host species<br/>Parasites work in concert with other stressors to<br/>affect hosts<br/>The impact of parasitism is influenced when<br/>hosts occur in small or fragmented populations.<br/>Parasites can strongly affect hosts with reduced<br/>genetic variation<br/>Captive host populations are often very vulnerable<br/>to parasites<br/>Parasites are frequently transferred from abundant<br/>host species to rare relatives, including from<br/>humans to our great ape cousins<br/>Farming can pose parasite problems for wild<br/>host species<br/>Parasites of an iconic symbol—the giant panda—<br/>point out our need to know more<br/>8.3 DANGERS RESULTING FROM SPECIES<br/>INTRODUCTIONS<br/>Parasites can be introduced with their hosts and have<br/>spillover effects<br/>Introduced hosts can favor indigenous parasites<br/>and cause spillback effects<br/>Sometimes introduced nonhost organisms can<br/>influence indigenous parasite transmission<br/>Invading hosts can benefit by leaving their natural<br/>enemies, such as parasites, behind<br/>Invasive hosts can potentially be controlled by<br/>parasites from their original range<br/>Introductions of parasites or hosts often fail<br/>Translocations of endangered host species can have<br/>unforeseen consequences<br/>Can invasional meltdown occur?<br/>8.4 PARASITES AS INDICATORS OF<br/>ENVIRONMENTAL HEALTH<br/>Parasites can help us monitor ecosystem integrity<br/>8.5 PARASITES AS INFERENTIAL TOOLS<br/>TO PRESERVE HOST BIODIVERSITY<br/>Parasites can provide information useful to<br/>preserving their hosts<br/>8.6 THE NEED TO PRESERVE PARASITE<br/>DIVERSITY<br/>Parasites play key roles in maint.lining ecosystem<br/>health<br/>Parasites are drivers of biodiversity<br/>Parasites are a source of pharmacological and<br/>therapeutic novelties<br/>Slip sliding away—parasite diversity is being lost<br/>REVIEW QUESTIONS<br/>REFERENCES<br/>CHAPTER 9 THE CHALLENGE OF<br/>PARASITE CONTROL<br/>9.1 STRATEGIES TO REDUCE PARASITE<br/>TRANSMISSION<br/>Parasite transmission may be reduced in various<br/>ways<br/>Parasites using trophic transmission can be<br/>controlled by insuring food safety<br/>Proper sanitation is the key to controlling parasites<br/>transmitted via the fecal-oral route<br/>Various other factors influence the success of<br/>control efforts<br/>The control of vector-borne diseases focuses on<br/>reducing human-vector contact<br/>The discovery of DDT radically altered vector<br/>control efforts<br/>Newer insecticides provide alternatives to DDT<br/>Transmission of vector-borne parasites can be<br/>reduced through environmental manipulation<br/>Biological control offers the possibility of low-cost,<br/>sustainable control<br/>The production of transgenic vectors provides hope<br/>as a means to reduce vector capacity<br/>9.2 ANTI-PARASITIC DRUGS<br/>Various factors influence the selection of the best<br/>anti-parasitic drug in different situations<br/>Different drugs may be appropriate for treatment<br/>and for prophylaxis<br/>Drugs may be used to either treat or protect<br/>individuals or to protect a population<br/>Certain drugs are active only against specific<br/>parasite life-cycle stages<br/>Drug use may affect the immune status of the<br/>population<br/>The use of anti-parasitic drugs can lead to resistance<br/>Genetic alterations can cause resistance in<br/>diverse ways<br/>Resistance poses a considerable problem for disease<br/>control programs<br/>Drug resistance can be prevented or reversed<br/>Concerns about resistance highlight the need for<br/>new anti-parasitic drugs<br/>New drugs are also needed to replace older more<br/>toxic medications<br/>The manner in which new drugs are discovered has<br/>changed considerably<br/>Potentially effective drugs usually require chemical<br/>modification prior to their use<br/>Economic issues often affect the rate at which<br/>new drugs are developed<br/>9.3 VACCINES<br/>Vaccines must be safe and inexpensive, while<br/>inducing long-term immunity<br/>Vaccines against eukaryotic parasites are<br/>particularly problematic<br/>Vaccines can be categorized into several types<br/>An effective malaria vaccine has been the object of<br/>intensive investigation<br/>Vaccines against different life-cycle stages offer<br/>different potential benefits<br/>Recent candidate vaccines may be used clinically<br/>in the near future<br/>A few anti-eukaryote vaccines are available for<br/>veterinary use<br/>Vaccines against helminth parasites are being<br/>investigated<br/>REVIEW QUESTIONS<br/>REFERENCES<br/>CHAPTER 10 THE FUTURE OF<br/>PARASITOLOGY<br/>10.1 OUR FUTURE WORLD<br/>10.2 SOME FUTURE CHALLENGES FOR<br/>PARASITOLOGISTS<br/>There is always something new to be found<br/>under the parasitological sun<br/>We need to better understand the ecological and<br/>evolutionary roles of parasites<br/>Revealing how parasite and host molecules<br/>interact is needed to clarify many fundamental<br/>aspects of parasitism<br/>Climate change will affect parasites, but we know<br/>little about how<br/>10.3 CONTROLLING PARASITES IN<br/>THE FUTURE<br/>Improved understanding of immunity should<br/>enable development of new anti-parasite vaccines,<br/>but so far the parasites are winning<br/>Chemotherapy-based control is an arms race<br/>between human ingenuity and parasite evolvability<br/>Integrated control may provide the best prospects<br/>for sustainable parasite control and is built on a<br/>thorough knowledge of parasite biology<br/>Major programs are underway to eliminate<br/>many parasites as public health problems<br/>We will need improved methods to detect low<br/>levels of parasite infection and transmission in<br/>the future<br/>Provision of improved living conditions, including<br/>education, wiU further discourage parasite<br/>transmission |
