Introduction to Parasitic Protozoa

1
Introduction to Parasitic Protozoa

• Not classified under Kingdom Animalia but under
  Kingdom Protista
• Main feature is they are unicellular eukaryotes
• First described some 300 years ago by
  Leeuwenhoek when he described Giardia from his
  own intestine.

2
Classification

• See Classification beginning on page 49
• Subject to much variation
• Four major types of organisms I will discuss
• Flagellated protozoa - Mastigophora
• Amoeba - Sarcodina
• Ciliated protozoa - Ciliophora
• Apicomplexa (sporozoans)

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Organelles of Locomotion of Mastigophorans

• Flagella

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Organelles of Locomotion of Mastigophorans

• Flagella

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Gardia lamblia trophozoite
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Microstructure of Cilium9 2 configuration
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Sarcodina have Pseudopoda
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Types of Nutrition

• Autotrophic Holophytic or photosynthetic
• Zooxanthellae which are found in many Cnidaria
  and other invertebrates are the best examples of
  these symbiots.
• Heterotrophic
• Holozoic nutrition
• Saprozoic nutrition

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Reproduction in the Protozoa

• Asexual reproduction
• Binary fission
• Multiple fission, merogony or schizogony (also
  sporogony)
• Budding

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Reproduction in the Protozoa

• Sexual reproduction
• Gametogony
• Syngamy
• Isogametes
• Anisogametes Macrogametes -
  Microgametes -
• Conjugation

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Trophozoite or Vegetative Stage

• Entamoeba Giardia lamblia

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Encystment

• Entamoeba Giardia lamblia

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Protozoa Overview

• Belong to Kingdom Protista
• Unicellular
• Eukaryotic
• Some very important parasites

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Family Trypanosomatidae

• Heteroxenous - most members have two phases in
  the life cycle
• first phase, they live in the blood or tissues of
  some vertebrate (often called hemoflagellates)
• second phase is found in the gut of some blood
  sucking invertebrate
• (monoxenous) - have a single host

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Forms found in Trypanosomatidae
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Trypanosomatidae forms
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Forms found in Trypanosomatidae
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Genus Trypanosoma

• most important flagellates
• divided into two broad sections based upon
  development in the invertebrate host
• Salivaria - (anterior station development) These
  accomodate transmission to vertebrate host during
  the blood meal of the arthropod.
• Stercoraria Posterior section development.
  Transmission occurs through fecal contamination

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Trypanosoma brucei complex

• Salivaria
• pleomorphic
• Vectors are members of the Tsetse fly (genus
  Glossina
• Live in the blood, lymph nodes and spleen, and
  cerebrospinal fluid of the vertebrate host

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Glossina
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Trypanosoma brucei complex

• Live in the blood, lymph nodes and spleen, and
  cerebrospinal fluid of the vertebrate host
• Trypanosoma brucei brucei parasite of antelopes
  and other African ruminants
• pathogenic to domestic ruminants causes nagana a
  type of sleeping sickness in animals

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Trypanosoma brucei gambiense.

• chronic form of African Sleeping Sickness
• west central and central Africa
• vectors include Glossina palpalis and G.
  tachinoides
• Game animals are not reservoir hosts.

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Trypanosoma brucei rhodiense

• acute form of African Sleeping Sickness
• east central and central Africa
• Glossina morsitans, G. pallidipes, and G.
  swynnertoni are the most important vectors
• Wild game animals are believed to serve as
  reservoir hosts.

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Pathology

• T. gambiense invades the central nervous system
  initiating a chronic, sleeping-sickness.
• apathy, mental dullness, tremor of hands, tongue,
  etc. followed by convulsions and paralysis.
• Sleeping follows with coma and death common.

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Pathology

• T. rhodiense does not attack the nervous system.
• causes a more rapid death
• rapid weight loss, heart involvement, and death
  can occur within a few months.
• Winterbottom's sign

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Diagnosis and Treatment

• Finding parasites in blood, bone marrow, or
  cerebrospinal fluid is diagnostic
• Winterbottoms sign
• Today the drug of choice is difluoromethylorithine
  (DFMO).

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Epidemiology and Control

• attempts to control the tsetse fly vectors.
• Vectors of T. brucie and T. rhodiense occur in
  open country, pupating in dry, soil
• vectors of T. gambiense are riverine flies
  breeding in shady, mosit areas along rivers.
• Tsetse flies are larviparous
• Brush removal is effective (febble flyers) but
  must be maintained.

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Glossina breeding habitat
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Cleared Strips to Control Trypanosoma gambiense
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Epidemiology and Control

• Chemical spraying with insecticides
• Elimination of wild game animals .
• selective breeding of cattle

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Other Salivarian Trypanosomes

• T. evansi Causes a disease in horses, camels,
  elephants, dogs, and other mammals called surra.
  Nearly 100 fatality to dogs and elephants if
  untreated
• can be mechanically transmitted by horseflies
• T. equiperdum no arthropod host. Veneral
  transmission, it causes dourine in horses.

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Stercoraria Trypanosomes

• Trypanosoma cruzi
• Chagus discovered the organism in 1910
• Infects cone-nosed bugs belonging to the family
  Reduviidae
• Causes Chagus disease in humans
• Distributed throughout Central and South America
  and infects over 19 million people

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Vectors of Trypanosoma cruzi
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Transmission

• Reduviid bugs usually defecate when they feed
• Feces contains the infective metacyclic
  trypanosomes.
• These enter the host body when the bite is
  scratched or mucous membranes
• enter a reticuloendothelial cell of the spleen or
  liver

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Transmission

• Become amasitgote forms and undergo rapid
  division. Cyst-like pockets of the amastigotes
  called pseudocyts are formed.
• Amastigotes complete development and enter the
  blood where they are infective to the insect
  vector
• Infective metacyclid trypomastigotes appear in
  the feces within 8 - 10 days.

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Pathogenesis of Chagus Disease

• Acute phase - most common in children under 5
  years
• Romana's sign
• Pseudocysts can form in almost any tissue Heart
  muscle ganglion cells are very susceptible and up
  to 80 of them may be destroyed.
• Death may occur within 3-4 weeks after infection.

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Romanas sign
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Pathogenesis of Chagus Disease

• Chronic stage is most often seen in adults.
• May last many years damaging heart muscle
  ganglion cells.
• In endemic areas, the disease may accont for 70
  of the cardiac deaths.
• megaesophagus or megacolon

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Pseudocyst of T. cruzi in heart
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Epidemiology

• Reduviidae bugs are the most important link to
  human transmission
• wild mammals may serve as reservoir hosts, dogs
  and cats are more important reservoirs for human
  disease.

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Epidemiology

• Transmission can also occur through blood
  transfusions, contaminated needles,
  transplacental transmission and ? Breast milk
• Thatcched roofs and cracked walls are ideal
  breeding and hiding places for the bugs

42
Diagnosis and Treatment

• Presence in the blood, cerebrospinal fluid, fixed
  tissues or lymph
• Xenodiagnosis is where laboratory reared bugs are
  allowed to feed on patients and then after a
  period of time they are examined for flagellates.
• Complement fixation and other immunodiagnostic
  tests