CHAP 4 PARASITOLOGY

• Parasitology


  The study of the interaction between parasites and their hosts
• Parasitology


  • Tends to concentrate on eukaryotic parasites, such as lice, mites, protozoa and worms, with prokaryotic parasites and other infectious agents the focus of fields such as bacteriology, microbiology and virology
• Parasite


  A living organism which receives nourishments and shelter from another organism where it lives
• Parasite


  An organism that is entirely dependent on another organism (host)
• Pathogenicity


  • The pathogenic mechanism of parasitic infection varies according to species and quantity of parasites as well as parasite-host adaptation and host responses
  • The damage caused by parasites can be either confined within the parasitic site or extend into other parts in host
  • Damages are commonly caused by mechanical pressure, capturing nutrition, toxins, responses and anaphylaxis of host to the stimulation from parasites as well as passage for other pathogens invading the host
• Pathogen


  An organism that causes diseases to the host after infection
• Parasite


  An organism that lives on or in another organism of another species, usually deriving nutrients at the expense of its host
• Pathogen


  Usually kill their host through diseases
• Parasite


  Most do not kill their host but do cause some damage
• Pathogen


  Typically do not require a host to complete its life cycle
• Parasite


  Will have to depend on their host to complete their life cycle
• Pathogenicity


  The ability of an organism to infect another organism (host)
• Parasitism


  A kind of interaction between two species, where one species is benefitted, and the other is harmed
• Definitive or Primary Host


  The host which harbors the adult parasites or where the parasite replicates sexually
• Definitive Hosts


  • Sheep for Fasciola gigantica
  • Dog for Echinococcus granulosus
  • Female anopheles mosquito for Plasmodium spp.
• Intermediate or Secondary Host


  The host which harbors the larval stages of a parasite or in which the parasite undergoes asexual multiplication
• Reservoir Host


  • A host which harbors the parasites, possibly grow, and multiply and serves as an important source of infection to other susceptible hosts
  • Does not get the disease carried by the pathogen or it is asymptomatic and non-lethal
• Paratenic or Storage Host


  • A host that serves as a temporary refuge and vehicle for reaching an obligatory host, usually the definitive host
  • Harbors the sexually immature parasite, but it cannot develop further in this host
• Incidental or Accidental Host


  A host organism that shelters the parasite, but since it can't progress the life cycle development, it is dead-end for it
• Symbiotic Relationships


  Host-parasite relationships in which the organisms (host and parasite) live in close proximity to each other and are dependent on each other in one or another way for their survival
• Types of Symbiotic Relationships


  • Parasitism
  • Mutualism
  • Commensalism
  • Phoresis
• Mutualism


  A symbiotic relationship where both organisms benefit from each other's existence
• Parasitism


  A non-mutual symbiotic relationship in which the parasite benefits at the expense of the host, while the host is harmed
• Commensalism


  A symbiotic relationship where one partner benefits while the second partner (the host) are neither helped nor harmed
• Parasitic Adaptation


  Any feature of an organism or its part which enables it to exist under conditions of its habitat
• Structural Adaptations


  • Feeding organs are usually absent in endoparasites
  • Presence of well-developed piercing devices to invade host tissue
  • Locomotory organs are generally absent or highly reduced in endoparasites
  • Presence of attachment organs like rostellum, hooks or suckers to securely connect to host organs
  • Outer covering resistant to host enzymatic digestion
  • Highly muscular pharynx for easy absorption of food materials from host
• Types of Parasites


  • Ectoparasites (live on host surface)
  • Endoparasites (live inside host)
• Types of Parasites


  • Permanent Parasites (parasitic throughout life)
  • Temporary Parasites (visit host for short period)
  • Facultative Parasites (can live parasitic or non-parasitic)
  • Obligatory Parasites (cannot exist without parasitic life)
  • Occasional Parasites (attack unusual hosts)
• Main Classes of Parasites


  • Protozoa
  • Helminths
  • Ectoparasites
• Protozoa


  • Microscopic, one-celled organisms that can be free-living or parasitic
  • Able to multiply in humans, contributing to survival and serious infections from a single organism
  • Transmitted through fecal-oral route or by arthropod vector
• Helminths


  • Large, multicellular organisms generally visible to the naked eye in adult stages
  • Cannot multiply in humans in adult form
  • Include flatworms (trematodes and cestodes), thorny-headed worms (acanthocephalins), and roundworms (nematodes)
• Protozoa


  Microscopic single-celled organisms that can live in the intestine, blood or tissue of humans
• Transmission of protozoa that live in a human's intestine to another human


  Typically occurs through a fecal-oral route
• Transmission of protozoa that live in the blood or tissue of humans to other humans


  By an arthropod vector (e.g. bite of a mosquito or sand fly)
• Helminths


  Large, multicellular organisms generally visible to the naked eye in their adult stages, can be free-living or parasitic
• In their adult form, helminths cannot multiply in humans
• Main groups of helminths


  • Flatworms (Platyhelminths) - trematodes (flukes) and cestodes (tapeworms)
  • Thorny-headed worms (Acanthocephalins) - reside in gastrointestinal tract
  • Roundworms (Nematodes) - reside in gastrointestinal tract, blood, lymphatic system or subcutaneous tissues
• Ectoparasites


  Organisms such as ticks, fleas, lice, and mites that attach or burrow into the skin and remain there for relatively long periods of time
• Arthropods are important in causing diseases in their own right, but are even more important as vectors, or transmitters, of many different pathogens
• Parasites and their associated diseases in humans

  • Acanthamoebiasis
  • Babesiosis
  • Balantidiasis
  • Blastocystosis
  • Coccidiosis
  • Amoebiasis
  • Giardiasis
  • Isosporiasis or cyclosporiasis
  • Leishmaniasis
  • Trichomoniasis
  • Trypanosomiasis (Sleeping sickness)
  • Chagas disease
  • Roundworm
  • Clonorchiasis
  • Diphyllobothriasis
  • Enterobiasis
  • Hookworm infection
  • Strongyloidiasis
  • Taeniasis (pork and beef tapeworm)
  • Toxocariasis
  • Trichinosis
  • Whipworm infection