Parasitic Protozoans Notes

Phylum Euglenozoa

Flagellated protozoans.
Class Saccostomae
- Order Kinetoplastida
  - Characteristics:
    - Have a large, single mitochondrion.
    - Kinetoplast: Densely packed network of circular DNA located within a single mitochondrion near the base of the flagellum.
  - Family Trypanosomastidae
    - Morphology:
      - Cells are elongated.
      - Uninucleate.
      - One flagellum.
    - Lifecycle:
      - Heteroxenous: Complex life cycle requiring two hosts.
      - Hemoflagellates.
    - Morphological Stages (general forms seen across the Family):
      - Amastigote:
        Spheroid.
        Short flagellum, projecting slightly from flagellar pocket.
        Observed in life cycle of Leishmania.
      - Choanomastigote:
        Free flagellum arises through a wide collar process.
        Observed in some species of Crithidia.
      - Promastigote:
        Elongated body with free flagellum.
        Kinetoplasts located in front of nucleus near anterior end of the body.
      - Opisthomastigote:
        Kinetoplast is found between nucleus and posterior end.
        No undulating membrane.
        Flagellum passes through the entire length of the body and opens at the anterior.
      - Epimastigote:
        Kinetoplast is located between nucleus and anterior.
        Short undulating membrane.
        In Crithidia and Blastocrithidia.
      - Trypomastigote:
        Kinetoplast is near the posterior end of the body.
        Flagellum runs along the surface and continues as a free whip at the anterior.
        Associated with an undulating membrane.
        Forms in Trypanosoma in the bloodstream.
  - Genus Trypanosoma
    - Characteristics:
      - All are heteroxenous (transmitted by animal vectors).
      - Various species pass through various morphological stages in invertebrate hosts.
      - Parasites of all classes of vertebrates.
      - Two categories (depending on the site of development in invertebrate host):
        Section Salivaria:
        Species that develop in the anterior portion of the digestive tract of invertebrate host.
        Section Stercoraria:
        Develop in hindgut of invertebrates.

Section Salivaria

Species: Trypanosoma brucei
- Subspecies:
  - T. brucei brucei
  - T. brucei gambiense
  - T. brucei rhodesiense
  - Characteristics:
    - Morphologically indistinguishable but produce different pathological symptoms.
  - Distribution:
    - Widely distributed in Africa.
  - Vectors:
    - Tse-Tse flies.
- T. brucei brucei
  - Causes NAGANA.
  - Sheep, goats, ox, horse, camel, pig, donkey, mule are reservoir hosts, and humans are not susceptible.
  - Vectors:
    - Glossina morsitans
    - G. pallidipes
    - G. swynnertoni
  - Pathogenesis:
    - Live in blood, lymph nodes, spleen, and CSF.
    - Do not invade cells but inhabit connective tissue spaces (reticular tissue spaces of spleen and lymph node).
  - Symptoms:
    - Anemia, edema, watery eyes and nose.
    - Fever.
    - Within a few days: emaciation, incoordination, paralysis --> death.
- T. brucei gambiense
  - Causes West African Sleeping Sickness/ Gambian Trypanosomiasis/ Mid African Sleeping Sickness.
  - Distribution: West Central and Central Africa.
  - Highly Pleomorphic.
  - Vectors:
    - Glossina palpalis
    - G. tachinoides
    - G. fuscipes
  - MOT (Mode of Transmission):
    - Insect bite.
    - Mechanical transmission.
    - Coitus.
    - Congenital transmission (rare).
  - Pathogenesis:
    - Sore develops at the site of inoculation.
    - Enlargement of lymph nodes.
      - Winterbottom’s sign.
    - Fever, headache, generalized pain, weakness, cramps.
    - Invasion of CNS-chronic stage.
      - Increased apathy.
      - Disinclination to work.
      - Mental dullness and disturbances of coordination.
      - Tremors of tongue, hand, and trunk.
      - Kerandel’s sign- pressure on palms followed by pain.
      - Sleepiness, coma, followed by death.
        T. brucei rhodesiense
  - Distribution:
    - Central and East Africa.
  - Causes more acute Sleeping Sickness.
  - Vectors:\n * G. morsitans
    - G. Pallidipes
    - G. swynnertoni
  - Pathogenesis:
    - Similar to T. gambiense.
    - Rarely invades the nervous system.
    - Causes a more rapid course towards death (9 months - 1 year).
    - Rapid weight loss.
    - No somnambulism.
- Diagnosis (general):
  - Parasite in blood, bone marrow, or CSF.
  - Serological tests.
  - Trypanosome may be seen from fluid aspirated from ulcer.
- Treatment:
  - Arsenical drugs (melarsoprol).
  - Suramin.
  - Pentamidine and berenit.
- Control of Glossina:
  - DDT and benzene hexachloride.
  - Bush removal and trimming.
  - People sit and catch fly.

Section Stercoraria

Species: Trypanosoma cruzi
- Discovered and studied before known to cause a disease.
- 1910 Carlos Chagas- found epimastigotes in the hindgut of Reduviid bugs.
- Causes CHAGAS DISEASE.
- Distribution:
  - South and Central America.
- Morphology:
  - Trypomastigote: slender, 15-20 $um$
  - Amastigote: spheroid, 1.5-4 $um$
- Vectors (Reduviid bugs- kissing bugs):
  - Triatoma sordida
  - T. brasiliensis
  - T. infestans
  - Rhodinus prolixus
- MOT:
  - Bugs defecate on skin; entry of metacyclic trypomastigote through:
    - bite
    - scratched skin
    - mucous membranes rubbed with contaminated finger.
- Life cycle (Triatomine Bug Stages and Mammalian Stages)
- Pathogenesis:
  - Acute Phase (common in children < 5 years):
    - Local inflammation along inoculation (CHAGOMA)- swelling of regional lymph nodes.
    - When enters conjunctiva:
      - Edema of eyelids.
      - Conjunctivitis.
      - Romana’s sign- swelling of periauricular lymph node.
    - Cardiac cells invasion.
    - Anemia.
    - Loss of strength.
    - Nervous disorder.
    - Chills.
    - Muscle and bone pain.
    - Death in 3-4 weeks.
  - Chronic Phase (common in adults):
    - Cause central peripheral nervous dysfunction.
    - Cardiac failure due to loss of muscle tone, heart enlargement, and flabby.
    - Megaesophagus/ Megacolon:
      - Muscle tone destroyed resulting in deranged peristalsis and gradual flabbiness.
      - Fatal when patient cannot swallow.
        *Diagnosis:
  - Presence of trypanosome in the blood, CSF, fixed tissues, or lymph.
  - Heart smear.
  - Immunodiagnostic tests: ELISA (Enzyme Linked Immunosorbent Assay).

Genus Leishmania

Characteristics:
- Heteroxenous, blood flagellates.
- Infects mammals: humans, dogs, and several species of rodents.
- Cause LEISHMANIASIS.
Biology:
- Promastigote- gut of fly.
- Amastigote (leishman- donovan bodies)- vertebrate tissues.
Life Cycle
- Vectors:
  - Sandflies
    - Phlebotomus
    - Lutzomyia
Species:
- Leishmania tropica
- L. major
  - Cause:
    - Cutaneous leishmaniasis
    - Oriental sore
    - Leppo boil
    - Jericho boil
    - Delhi boil
    - Baghdad boil
  - Distribution:
    - West Central Africa
    - Mediterranean
    - Middle East
    - Asia Minor into India
  - Vectors
    - P. papatasii - L. major
    - P. sergenti - L. tropica
  - Pathology
    - L. tropica
      - Dry lesions with numerous amastigotes within.
    - L. major
      - Moist lesions with few amastigotes.
      - Ulcerations are secondary to anoxia from cellular infiltrates.
Diagnosis
- For lesions: based on elevated and indurated margins of ulcer.
- Impression smears from biopsies or scrapings from lesion edges.
- Intradermal testing using Leishmanial promastigote Ag.
Treatment
- Antimony compounds
- Ketaconazole

Order Retortamonadida

Family Retortamonadidae
- Species: Chilomastix mesnili
  - Morphology:
    - Trophozoite: pyriform, posterior drawn out into a blunt form
      - 6-24 $um$ x 3-10 $um$ , with cytostomes
      - 4 flagella (one longer than the others)
      - Large nucleus
    - Cyst: in formed stool
      - Thick walled
      - 6.5-10 $um$ long
      - Pear/lemon shaped
      - One nucleus, retains all nucleus
  - MOT:
    - Ingestion of cyst (contaminated drink and foods)
  - Pathogenesis:
    - May cause watery stool, non-pathogenic in general

Order Diplomonadida

Family Hexamitidae
- Species: Giardia lamblia
  - Morphology
    - Lack mitochondrion, smooth ER, golgi bodies, lysosomes
    - 12-15um long
    - Rounded at anterior end, pointed posterior
    - Dorsoventrally flattened, convex on the dorsal surface
    - 4 pairs of flagella
    - Median bodies- pair of large cytoskeletal organization, curved transverse dark-staining bodies
  - Life cycle
  - Pathogenesis
    - Does not lyse host cells but feeds on mucus secretions
    - Dense coat of Giardia interferes with fat absorption
  - Symptoms
    - Increased mucus secretions
    - Diarrhea
    - Intestinal pain
    - Flatulence
    - Weight loss
    - Fatty stool, but never bloody
    - Gall bladder may become infected: jaundice
  - Diagnosis
    - Recognition of trophozoite or cyst in stained fecal smear
    - Duodenal aspiration
    - Immunodiagnostic method: detection of serum Ab or Ag in feces
  - Treatment
    - Quinacrine or metronidazole

Order Trichomonadida

Family Trichomonadidae
- Species: Trichomonas vaginalis
  - Morphology
    - 7-32 $um$ x 5-12 $um$
    - shorter undulating membrane
  - MOT
    - sexual intercourse
    - from soiled washclothes
    - towels and clothing
    - passage of infant in birth canals
    - contaminated toilets
    - acidity of vagina discourages infection, once established, the organisms causes a shift to alkalinity
  - Pathogenesis/Symptoms
    - intense inflammation with itching
    - after few days: degeneration of vaginal epithelium, vaginal secretion (white and greenish)
    - in men: asymptomatic
  - Diagnosis
    - recognition of trichomonad in secretion of vagina or from in vitro culture made from vaginal irrigation
    - urinalysis
    - DOT-BLOT DNA hybridization assay
  - Treatment
    - Metronidazole
    - Suppositories and douches: promote acid pH in vagina
    - sexual partners should be treated simultaneously

Order Amoebida

General characteristics
- posses shapeless bodies
- with wide, blunt, thin, pointy pseudopodia
- may be naked, or in a TEST or shell- secreted by cytoplasm
- move by cytoplasmic streaming
Species: Entamoeba histolytica
- Morphology
  - Trophozoites
    - amorphous
    - move by pseudopodia
    - with granular endoplasm
  - Cyst (infective form)
    - round or oval
    - 12-15 $um$ in diameter
    - have highly retractile cyst wall- resistant to gastric juices
    - mature cyst- quadri-nucleated
    - cytoplasm: shows chromatid bars, no RBCs
- Life Cycle
  - Excystation
  - Trophozoites
  - Multiplication
  - Cysts
  - Trophozoites exit host
- Pathogenesis
  - intestinal amebiasis
    - dysentery
    - colitis
    - appendicitis
    - toxic megacolon
    - amebomas
  - Extraintestinal amebiasis
    - liver abscess
    - peritonitis
    - pleuropulmonary abscess
    - cutaneous lesions
    - amebic lesions
- Diagnosis
  - biopsy
  - stool microscopy
  - stool Ag detection
  - stool culture
  - serology
  - PCR
  - radiological findings
  - blood test
  - liver function test
  - kidney function test
  - intradermal test

Phylum Percolozoa

Class Heterolobosea
- Order Schizopyrenida
  - Family Vahlkampfiidae
    - Species Naegleria fowleri
      - Morphology
        Trophozoites
        10-35 $um$
        limax-like with sticky posterior end
        posses food cups (amoebostomes)
        Flagellates
        pear shaped (10-35 $um$ )
        transition from trophozoite, the vacuoles decreases and flagella forms due to nutritional deficiency
        not capable of reproduction
        Cysts
        mucoid plug seals cyst wall spores
        contains nucleus, several vacuoles
        incapable of reproduction
      - Life Cycle
        Naegleria fowleri is found in fresh water, soil, thermal discharges of power plants, heated swimming pools, hydrotherapy and medicinal pools, aquariums, and sewage
        Trophozoites can turn into temporary flagellated forms which usually revert back to the trophozoite stage.
        Trophozoites infect humans or animals by entering the olfactory neuroepithelium and reaching the brain. N. fowleri trophozoites are found in cerebrospinal fluid (CSF) and tissue, while flagellated forms are found in CSF
      - Pathogenesis
        aerobic heterotrophic organisms
        brain is an oxygen-rich environment with conducive conditions that allow the organism to survive as a parasitic pathogen
        young and adults are more vulnerable because cribriform plate is porous
      - Symptoms (similar to bacterial meningitis)
        initial symptoms (PAM)- starts 5 days after infection)
        headache, fever, nausea, or vomiting
        later symptoms
        stiff neck, confusion, lack of spatial awareness, loss of balance, seizures, and hallucinations
        progresses rapidly leading to death (>12 days)NOTE