PROTOZOA (MICROPARA)

• 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 into cyst forms
• Excystation


  Process by which cysts differentiate into trophozoite forms
• Protozoa


  • Single-celled eukaryotic organisms that are spherical to oval or elongated in shape
  • Not all protozoa are parasitic, some are facultative parasites capable of a free-living state
  • The majority divide by means of binary fission
  • Sporozoans reproduce through both sexual and asexual means
• Protozoan infections are most often diagnosed through microscopic examination of body fluids, tissue specimens, or feces
• Special stains may be used to demonstrate the different protozoa
• Trophozoite


  The motile (with pseudopods or "false feet") and the feeding form, the pathogenic stage
• Cyst


  The non-motile form, the infective stage for most intestinal protozoan parasites
• Trichomonas vaginalis exists only in the trophozoite form (infective and pathogenic)
• Entamoeba histolytica


  • An intestinal and tissue ameba, the only known pathogenic intestinal ameba
  • Its life cycle consists of two stages - the non-motile cyst (infective stage) and the motile trophozoite (pathogenic stage)
• Giardia lamblia


  • An intestinal protozoan, exists in a cyst form and a trophozoite form
  • The trophozoite is pear-shaped or teardrop-shaped with four pairs of flagella and a sucking disc to attach to intestinal villi
  • The cyst is oval and thick-walled with four nuclei
• Trichomonas vaginalis


  • A pear-shaped organism with a central nucleus, four anterior flagella, and an undulating membrane
  • Exists only in the trophozoite form (infective and pathogenic)
• Balantidium coli


  • The largest protozoan to infect humans, has a primitive mouth called a cytostome, a nucleus, food vacuoles, and a pair of contractile vacuoles
  • The infective stage is the cyst and the pathogenic stage is the trophozoite, which invades the mucosal lining of the terminal ileum, cecum, and colon
• 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 into cyst forms
• Excystation


  Process by which cysts differentiate into trophozoite forms
• Protozoa


  • Single-celled eukaryotic organisms that are spherical to oval or elongated in shape
  • Not all protozoa are parasitic, some are facultative parasites capable of a free-living state
  • The majority divide by means of binary fission
  • Sporozoans reproduce through both sexual and asexual means
• Protozoan infections are most often diagnosed through microscopic examination of body fluids, tissue specimens, or feces
• Special stains may be used to demonstrate the different protozoa
• Trophozoite


  The motile (with pseudopods or "false feet") and the feeding form, the pathogenic stage
• Cyst


  The non-motile form, the infective stage for most intestinal protozoan parasites
• Entamoeba histolytica


  • An intestinal and tissue ameba, the only known pathogenic intestinal ameba
  • Its life cycle consists of two stages - the non-motile cyst (infective stage) and the motile trophozoite (pathogenic stage)
• Entamoeba histolytica life cycle


  1. Ingested cyst undergoes excystation in the ileum where it differentiates into a trophozoite

  2. Trophozoites colonize the cecum and colon

  3. Trophozoites may undergo encystation and become cysts passed out with feces
• Trophozoites of E. histolytica secrete enzymes that cause local necrosis producing the typical "flask-shaped" ulcer
• Invasion of the portal circulation may occur leading to the development of abscess in the liver
• Giardia lamblia


  • Intestinal protozoan, exists in cyst and trophozoite forms
  • Trophozoite is pear-shaped or teardrop-shaped with four pairs of flagella and a sucking disc to attach to intestinal villi
  • Cyst is oval and thick-walled with four nuclei
• Giardia lamblia life cycle

  1. Cyst ingested, undergoes excystation in duodenum

  2. Trophozoites attach to duodenal mucosa through sucking discs
• Trichomonas vaginalis


  • Pear-shaped organism with four anterior flagella and an undulating membrane, exists only in trophozoite form
• Trichomonas vaginalis pathogenesis


  1. Invades vaginal mucosa of infected women, multiplies through binary fission

  2. Feeds on local bacteria and leukocytes

  3. In men, most common site is prostate gland and urethral epithelium
• Balantidium coli


  • Largest protozoan to infect humans, has a primitive mouth, nucleus, food vacuoles, and contractile vacuoles
  • Infective stage is the cyst, pathogenic stage is the trophozoite which invades the mucosal lining of the terminal ileum, cecum, and colon
• All sexual partners of an individual with the infection must be simultaneously treated to prevent "ping pong" infections
• Balantidium coli


  • Morphologically more complex than E. histolytica
  • Has a primitive mouth called a cytostome, a nucleus, food vacuoles, and a pair of contractile vacuoles
  • The infective stage is the cyst and the pathogenic stage is the trophozoite, which invades the mucosal lining of the terminal ileum, cecum, and colon
  • The trophozoites typically exhibit rotary, boring motility (through cilia) and contain two nuclei (a small-dot-like micronucleus adjacent to a kidney bean-shaped macronucleus)
  • The cyst also contains two nuclei although the micronucleus may not be readily observable
• Acanthamoeba castellani


  • Together with Naegleria, is a minor protozoan pathogen but unlike Naegleria, Acanthamoeba usually causes infection in immunocompromised patients
  • It is a free-living amoeba that causes inflammation of the brain substance and its meningeal coverings (meningoencephalitis)
  • The parasite is found widely in soil, contaminated freshwater lakes, and other water environment
  • It is able to survive in cold water
  • Like E. histolytica, the infective stage is the cyst while the pathogenic stage is the trophozoite
• Naegleria


  • Similar to Acanthamoeba, the parasite Naegleria is also classified as a free-living protozoan
  • It shares many characteristics with Acanthamoeba
  • The parasite is also found worldwide in soil and contaminated water environments
  • Unlike Acanthamoeba, Naegleria can survive in thermal spring water
  • The known pathogen worldwide is Naegleria fowleri, which is the only amoeba with three identified morphologic forms—trophozoite, flagellate, and cyst forms
  • The trophozoite exhibits the typical amoeboid motility which is described as "slug-like"
  • The flagellate form is pear-shaped and is equipped with two flagella that are responsible for the parasite's jerky or spinning movement
  • The non-motile form is the cyst
  • The amoeboid trophozoite form is however the only form that is known to exist in humans
• Leishmania spp.


  • The life cycle of the parasite involves a vector, the female sandfly of the Phlebotomus and Lutzomyia genera
  • Leishmania spp. are obligate intracellular parasites
  • It has three morphologic forms—the amastigote, promastigote, and epimastigote
  • The infective stage is the promastigote
  • The promastigote form may be seen only if a blood sample is collected and examined immediately after transmission
  • Epimastigotes are found primarily in the vector
  • The pathogenic stage and diagnostic form are the amastigote which is found primarily in tissue and muscle, as well as the central nervous system within macrophages and in cells of the reticuloendothelial system
  • The typical amastigote is round to oval in shape and contains a nucleus, a basal body structure called a blepharoblast, and a small parabasal body located adjacent to the blepharoblast
  • Both the blepharoblast and parabasal body are collectively known as the kinetoplast
  • The promastigote is long and slender, with a kinetoplast located in its anterior end, and a single free flagellum extending from the anterior portion
• Montenegro skin test


  Similar to the tuberculin skin test for the diagnosis of tuberculosis
• Montenegro skin test


  • Used as screening for large populations at risk but is not used for diagnosis
  • Definitive diagnosis is done by demonstration of the amastigote from Giemsa stained slides of specimens from blood, bone marrow, lymph nodes, and biopsies of infected areas
• Diagnosis of leishmaniasis


  1. Culture of blood, bone marrow, and other tissues may also be done, which will show the promastigote forms

  2. Serologic tests are now also available such as an indirect fluorescent antibody (IFA), enzyme-linked immunosorbent assay (ELISA), or direct agglutination test (DAT)