MODULE 4B

• SOURCE OF INFECTION is when a parasite comes in contact with/ soil or water and other intermediate hosts.
• MODE OF TRANSMISSION is when parasites come in contact w/ humans
• INFECTIVE STAGE is when a parasite enters and establishes residence in or on humans.
• PATHOGENIC STAGE is when a parasite multiplies and competes w/ humans for nutritional needs.
• DIAGNOSTIC STAGE is when a parasite emerges from humans.
• There are two major classifications of parasites which are SINGLE CELLED PROTOZOA and MULTI CELLULAR METAZOAN.
• SINGLE CELLED PROTOZOA is produced through binary fission.
• SINGLE CELLED PROTOZOA has four groups which are based on their means of motility and mode of reproduction; these are AMOEBA, FLAGELLATES, SPOROZOA, and CILIATES.
• AMOEBA moves by the means of pseudopodia.
• FLAGELLATES are equipped with one or more whip- like flagella that enable them to move.
• SPOROZOA undergo both sexual and asexual reproduction and they do not possess any organ for motility.
• CILATES possess rows or patches of cilia that serve as their organs of locomotion.
• MULTI-CELLULAR METAZOAN also called HELMINTHS or WORMS.
• MULTI-CELLULAR METAZOAN has two phyla; NEMATHELMINTHES (roundworms) and PLATYHELMINTHES (flatworms).
• INFECTIVE STAGE refers to the stage of the parasite that enters the host or the stage that is present in the parasite’s source of infection.
• PATHOGENIC STAGE refers to the stage of the parasite that is responsible for producing the organ damage in the host leading to the clinical manifestations.
• ENCYSTATION process by which trophozoites differentiate/convert into cyst forms.
• EXCYSTATION process by which cysts differentiate/convert into trophozoite forms
• KINGDOM PROTOZOA consists of single-celled eukaryotic organisms that are spherical to oval or elongated in shape.
• The majority of Protozoa undergo the means of BINARY FISSION (Flagellates, Ciliates, Amoeba).
• Sporozoans (Plasmodium) reproduce through both SEXUAL AND ASEXUAL means.
• TROPHOZOITE – is the motile and pathogenic stage. It is found within the intestinal and extra-intestinal lesions, and in diarrheal stools
• CYST is called the dormant, non-motile form, and infective stage of protozoans. It is usually found in non-diarrheal, formed stools.
• More than 50,000 species of Protozoa have been described, most of which are free-living organisms; protozoa are found in almost every possible habitat
• Virtually all humans have protozoa living in or on their body at some time, and many persons are infected with one or more species throughout their life
• Commensals


  Protozoa that are normally not harmful
• Pathogens


  Protozoa that usually produce disease
• Protozoan diseases range from very mild to life-threatening
• Individuals whose defenses are able to control but not eliminate a parasitic infection become carriers and constitute a source of infection for others

  
• In geographic areas of high prevalence, well-tolerated infections are often not treated to eradicate the parasite because eradication would lower the individual's immunity to the parasite and result in a high likelihood of reinfection

  
• General life cycle of parasites


  1. Source of infection

  2. Mode of transmission

  3. Infective stage

  4. Pathogenic stage

  5. Diagnostic stage

  
• Two major groups of parasites


  • Single-celled protozoa
  • Multi-cellular metazoan (helminths or worms)
• Four groups of protozoa (based on means of motility and mode of reproduction)


  • Amoeba and flagellates
  • Sporozoa
  • Ciliates
• Two phyla of multi-cellular metazoan parasites


  • Nemathelminthes (roundworms)
  • Platyhelminthes (flatworms)
• Two classes of Platyhelminthes

  • Trematoda (flukes)
  • Cestoda (tapeworms)
• Infective stage


  The stage of the parasite that enters the host or the stage that is present in the parasite's source of infection

  
• Pathogenic stage


  The stage of the parasite that is responsible for producing the organ damage in the host leading to the clinical manifestations

  
• Encystation


  Process by which trophozoites differentiate/convert into cyst forms
• Excystation


  Process by which cysts differentiate/convert into trophozoite forms
• Protozoa


  • Single-celled eukaryotic organisms that are spherical to oval or elongated in shape
  • Classification is mainly based on the organ of locomotion utilized
  • Majority undergo binary fission, while sporozoans reproduce through both sexual and asexual means