lesson 9 (units: 1, 2, 3 & 4)

• Only the parasitic protozoa contains the microbes, helminths and arthropods does not have 
• 5 nationally notifiable parasitic diseases , 4 of them are Protozoal diseases and and one helminth disease ( Cryptosporisiosis, Cyclosporiasis, Giardiasis, malaria, trichinellosis
• Parasitic infections are most often diagnosed by observing and recognizing a particular life cycle stage in a clinical specimen
• Parasitism

  ✔ Is a symbiotic relationship that is of benefit to one party or symbiont ( parasite ) at the expense of the other party ( host )

  ✔ Also defined as an organism that live on or in other living organisms ( hosts ), at whose expense they gain some advantage

  ✔ Not all parasites cause disease, but they can deprive the host of nutrients and it is detrimental to the host
• Definitive Host - Is the one that harbors the adult or sexual stage of the parasite or the sexual phase of the life cycle
• Intermediate host - Harbors the larval or asexual stage of the parasite or the asexual phase of the life cycle
• Ectoparasites

  - Parasites that live outside the host’s body 

  • Examples are : Arthropods such as mites, ticks, and lice
• Endoparasites

  - Parasites that live inside the host’s body 

  ✔ Examples : Parasitic protozoa and Helminths
• Accidental host - Is a living organism that can serve as a host in a particular parasite’s life cycle
• Facultative parasites

  • Is 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 the host
  • Examples are : free living amebae that causes keratoconjuctivitis and primary emebic meningoencephalitis

   
• Obligate Parasite

  • It must be a parasite in order to survive. 

  ✔ Examples : most parasites that infect humans

   
• “Worm Burden” is often used in helminths.
• Ways in which parasites cause disease:

  1.Toxins produced 

  2. Harmful enzymes 

  3. Physical damage to tissues and organs 

  4. Occludes blood vessels and other tubular structures 

  5. Interferes with vital processes of the host 

  6. Deprives the host of essential nutrients 
• Most protozoa are unicellular, but some are multicellular ( colonial ) 
•  Protozoa can also be classified taxonomically by their mode of locomotion.
• Some move by pseudopodia ( false feet ) like Amebae , others move by flagella ( whiplike flagella) like the flagellates, others by cilia ( hairlike cilia ) like the ciliates.
•  Sporozoa have no means of locomotion, thus , they are called non-motile.
• Not all protozoa are parasitic like the pond water protozoa ( Paramecium and stentor spp ) 
• Facultative parasites 

  ■ Examples are the Acanthamoeba spp and Naegleria fowleri ,are capable of free living nonparasitic, however, they can can become parasites if they accidentally gain entrance to the body 

  ■ Acanthamoeba and N. fowleri resides in soil or water and gains entrance to the eyes of nasal mucosa, and can travel via olfactory nerve into the brain causing diseases in the CNS
• Protozoans are tiny 
• Infections caused by protozoa are often diagnosed with microscopic examination of fluids, tissue specimens or feces.
• Giemsa Stain - to stain peripheral blood smears 
• Trichrome, Iron Hematoxylin, Acid Fast Stain - to stal fecal specimens 
• Parasitic protozoal infections are diagnosed by observing trophozoites, cysts, oocysts or spores
• Trophozoites - is the motile, feeding, dividing stage in the protozoan’s life 
• Cysts, oocysts or spores - dormant stages 
• Entry 

  ◆ Primarily acquired by inhalation or ingestion of oocysts or spores 

  ◆ Injection via the bite of an infected arthropod