What are the 4 types of hosts?

Parasitology and pathogenesis

There are three species of schistosome that commonly cause disease in humans:Schistosoma mansoni,S. haematobium andS. japonicum. S. mekongi andS. intercalatum also affect humans but have a very restricted distribution (Fig. 20.34). Eggs are passed in the urine or faeces of an infected person and hatch in freshwater to release the miracidia. These ciliated organisms penetrate the tissue of the intermediate host, a species of water snail specific to each species of schistosome. After multiplying in the snail, large numbers of fork-tailed cercariae are released back into the water, where they can survive for 2–3 days. During this time the cercariae can penetrate the skin or mucous membranes of the definitive host, humans. Transforming into schistosomulae, they pass through the lungs before reaching the portal vein, where they mature into adult worms (the male is about 20 mm long and the female a little larger). Worms pair in the portal vein before migrating to their final destination: mesenteric veins in the case ofS. mansoni andS. japonicum, and the vesicular plexus forS. haematobium. Here they may remain for many years, producing vast numbers of eggs. The majority of these are released in urine or faeces, but a small number become embedded in the bladder or bowel wall and a few are carried in the circulation to the liver or other distant sites.

The pathology of schistosome infection varies with species and stage of infection. In the early stages, there may be local and systemic allergic reactions to the migrating parasites. As eggs start to be deposited, there is a local inflammatory response in the bowel or bladder, while ectopic eggs may produce granulomatous lesions anywhere in the body. Chronic heavy infection, in which large numbers of eggs accumulate in the tissues, leads to fibrosis, calcification and, in some cases, dysplasia and malignant change. Morbidity and mortality are related to duration of infection and worm load, as well as to the species of parasite. Children in endemic areas tend to have the heaviest worm load because of both increased exposure to infection and differences in the immune response between adults and children.

Introduction

Parasitology is the study of parasites and is traditionally limited to parasitic protozoa, helminths, and arthropods. Human parasitology is focused on medical parasites and includes their morphology, life cycle, and the relationship with host and environment.

Broadly speaking there are two types of parasites: endoparasites and ectoparasites. Endoparasites live within the host. They may be obligate parasites (dependent on their hosts and cannot live without the host), facultative parasites, and accidental parasites. Ectoparasites are parasites which live on the outer surface of the host.

Life cycle of parasites varies. Some have simple life cycle where all the developmental stages are completed in a single host. In others two different hosts are required. One is the definitive host and the other intermediate host. The definitive host is the one which harbors the adult parasite and where the parasite reproduces sexually. The intermediate host is the host which harbors the larval stage or the asexual forms of the parasite. Few parasites require two different intermediate hosts in addition to a definitive host.

Parasites are transmitted by various routes. These include, oral route, penetration by skin or mucous membrane, inoculation by arthropod vectors, and lastly by sexual contact.

Clinical features as a result of parasitic infestations may vary; some are acute, whereas most are chronic.

Diagnosis of parasitic infections depends on clinical diagnosis and laboratory diagnosis. Laboratory diagnosis includes documentation of characteristic forms of the parasites in the feces, urine, sputum, body secretions, or blood. Serologic tests are also available for certain parasites.

Abstract

Traditional parasitology includes the study of any eukaryotic organism that lives on, off, and at the expense of another organism. With the development of mathematical models describing parasite population biology, however, conventional exceptions such as bacteria and viruses are now included as parasites. Balkanized subdisciplines were thus combined with the one dealing with eukaryotic parasites, creating a more unified approach to parasitism. The overdispersion concept emerged as a quantitative assessment for the distribution of certain parasites within host populations. Mathematical modeling of parasite population biology and overdispersion were responsible for developing an innovative methodology for interpreting the dynamic nature of host–parasite interactions. Other new concepts and the application of some older ones, in addition to modeling and dispersion, included codification of parasite population and community biology, competition, colonization strategies, host and site specificity, emerging infectious disease, and food web ecology.

References

Alexander J (1988) Parasitology 96: 297–302.

Ashman RB et al (1993) Immunology and Cell Biology 71: 221–225.

Bartman T et al (1994) Virology 203: 1–7.

Berrettini WH et al (1994) Nature Genetics 7: 54–58.

Dessaro G et al (1995) Brain Research 671: 131–140.

Ferrarro TN et al (1995) Epilepsia 36: 301–307.

Flory CM et al (1992) Journal of Leukocyte Biology 51: 225–229.

Kita E et al (1992) Journal of Leukocyte Biology 51: 244–250.

Klein J et al (1983) Immunogenetics 17: 553–596.

Mori A et al (1990) International Archives of Allergy and Applied Immunology 92: 100–102.

Phillips TJ et al (1994) Alcholism, Clinical and Experimental Reserach 7: 54–58.

Reed SG et al (1994) Journal of Immunology 153: 3135–3140.

Rhodes JC et al (1980) Infection and Immunity 29: 494–499.

Stevenson MM et al (1982) Infection and Immunity 38: 80–88.

Takeda M et al (1993) International Journal of Experimental Pathology 74: 493–499.

Tolliver BK et al (1995) Pharmacology, Biochemistry and Behavior 50: 163–169.

Tucker PK et al (1992) Mammalian Genome 3: 245–261.

Yong Z et al (1988) Microbial Pathogenetics 4: 305–310.

3.4.6.2 Host responses to infection

Host parasite interactions are crucial for parasitology studies. The host gene array complements to the parasite gene array and studying the host cell undergoing infection, transcription profiling, growth latency, and mortality gives a clear idea about the development and survival of parasites in the host cell. These interactions can be explored by three ways: (1) Understanding and establishment of parasite infection in the host cell and initiation of an immune response; (2) Induction of immune responses stimulated by parasite; (3) Determining if the host transcripts facilitate the host or the parasite. The closely connected genes may have some difficulty. It should be assured that the signal detected is not because of cross-hybridization between host DNA printed on the microarray and parasite transcripts. The ribosomal protein genes are the among the ones that are highly conserved, hence hybridization could occur between them (Diehn et al., 2000). The host genes controlled during parasitic infection are broadly divided into three different categories: pro-host genes that increases host survival, pro-parasite genes which increases the survival of parasite, and the bystander genes that are regulated during regulation of first two genes. Microarray-based tests are based on the involvement of transcripts and pathways that offer several reporter assays, supporting in the detection of these factors (Boothroyd, Blader, Cleary, & Singh, 2003).

Introduction

The intersection between invasion biology, parasitology, and animal behavior is, at its most basic, an interaction among two species: an invasive parasite may adapt to a native host, or an invasive host could become infected with a parasite. The reality, as is often the case with animal behavior, is typically more complex, involving multiple host species and/or multiple parasite species. Examination of interactions among multiple species – and the behaviors that guide them – requires a community-wide approach. The mechanisms influencing a biological community, including parasitism, predation, and competition, must be taken into account as well.

A seminal experiment that first examined the dynamics of a parasite's effect on species interactions was completed by Thomas Park in 1948. Over a period of 4 years, 211 populations of flour beetles where sustained in a laboratory. These populations consisted of two species, Tribolium confusum or T. castaneum, which were either maintained alone or in mixed species colonies. Mixed-species colonies displayed marked competitive interactions, with one species always going extinct during the experiment. Park also added a naturally occurring protozoan parasite to some mixed-species populations and the results were striking: T. castaneum often went extinct when the parasite was present, but T. confusum died out when the parasite was absent. These were the first results to demonstrate the existence of parasite-mediated competition, leading to a flurry of research on parasites and their ability to regulate host populations, thus influencing the structure of biological communities.

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