parasitology

• Parasitism


  A symbiotic relationship that is of benefit to one party or symbiont (the parasite) at the expense of the other party (the host)
• Although many parasites cause disease, some do not
• Even if a parasite is not causing disease, it is depriving the host of nutrients
• Parasitic relationships are always considered detrimental to the host
• Parasite


  An organism that lives on or in other living organisms (hosts) at whose expense they gain some advantage
• Types of parasites


  • Plant parasites
  • Animal parasites
• Ectoparasites


  Parasites that live outside the host's body
• Endoparasites


  Parasites that live inside the host
• Ectoparasites


  • Arthropods such as mites, ticks, and lice
• Endoparasites


  • Parasitic protozoa and helminths
• Definitive host


  The host that harbors the adult or sexual stage of the parasite or the sexual phase of the life cycle
• Intermediate host


  The host that harbors the larval or asexual stage of the parasite or the asexual phase of the life cycle
• Parasite life cycles range from simple to complex
• Knowing the life cycle of a particular parasite enables epidemiologists and other healthcare professionals to control the parasitic infection through intervention at some point in the life cycle
• Accidental host


  A living organism that can serve as a host in a particular parasite's life cycle, but is not a usual host in that life cycle
• Dead-end host

  An accidental host from which the parasite cannot continue its life cycle
• Facultative parasite


  An organism that can be parasitic but does not have to live as a parasite, and is capable of living an independent life, apart from a host
• Obligate parasite


  A parasite that has no choice but to survive as a parasite
• Most parasites that infect humans are obligate parasites
• Parasitology


  The study of parasites
• Parasitologist


  Someone who studies parasites
• Medical parasitology


  The study of parasites that cause human disease
• In general, parasitic infections are diagnosed by observing and recognizing various parasite life cycle stages in clinical specimens
• Worm burden


  The number of helminths (worms) that are present
• Ways parasites can cause damage to their host


  • Produce toxins
  • Produce harmful enzymes
  • Cause physical damage to tissues and organs
  • Cause the destruction of individual cells
  • Cause occlusion of blood vessels
• Some parasites interfere with vital processes of the host
• Some parasites deprive their host of essential nutrients
• The host immune response to the presence of parasites or their products causes more injury than do the parasites themselves
• Protozoa


  Unicellular organisms in the kingdom Protista, together with algae
• Not all protozoa are parasitic
• Classification of protozoa by mode of locomotion


  • Amebas (amebae) - move by means of pseudopodia
  • Flagellates - move by means of whip-like flagella
  • Ciliates - move by means of hair-like cilia
  • Sporozoa (sporozoans) - have no pseudopodia, flagella, or cilia, and therefore exhibit no motility
• Because protozoa are tiny, protozoal infections are most often diagnosed by microscopic examination of body fluids, tissue specimens, or feces
• Trophozoite


  The motile, feeding, dividing stage in a protozoan's life cycle
• Cysts, oocysts, and spores


  Dormant stages (much like bacterial spores) in a protozoan's life cycle
• Protozoal infections are primarily acquired by ingestion or inhalation of cysts, oocysts, or spores
• Trophozoites rarely serve as the infective stages due to their fragile nature
• Helminth


  Parasitic worm
• Helminths are not microorganisms, but the various procedures used to diagnose helminth infections are performed in the Parasitology Section of the Clinical Microbiology Laboratory
• Helminths that infect humans are always endoparasites
• Major divisions of helminths


  • Roundworms (nematodes)
  • Flatworms (tapeworms (cestodes) and flukes (trematodes))