Toxoplasma gondii

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Toxoplasma gondii
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Toxoplasma gondii

• Important human disease especially for
  immunosuppressed individuals
• Heteroxenous life cycle
• Asexual in vertebrate intermediate hosts
• Carnivorous mammals and birds are the definitive
  hosts
• Sexual reproduction in cats only
• Oocyst consists of 2 sporocyst, each with 4
  sporozoites
• Have intestinal and tissue phases

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Definitions

• Schizogeny asexual reproduction that results
  from multiple mitosis by simultaneous
  cytokinesis, creates many daughter cells
• Occurs in the definitive host
• Merozoites daughter cell from schizogeny
• Tachyzoites rapidly dividing
• Bradyzoites slowly dividing
• Tachyzoites and bradyzoites are different
  immunologically

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T. gondii

• Intracellular organism that is usually in the
  cytoplasm
• Life cycle includes enteroepithelial
  (intestinal-epithelia) and extraintestinal
  tissues in cats and only extraintestinal in other
  hosts

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T. gondii - Extracellular

• Liver with infected cell in the center (arrow)
  and a necrotic area above
• Tachyzoites in fluid smear
• Stage of infection usually produces mild, if any,
  symptoms in healthy persons, but can be lethal in
  immunocompromised individuals, (acquired
  toxoplasmosis), and can cause severe damage to
  the fetus if transmitted transplacentally
  (congenital toxoplasmosis)

10 mm

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Zoitocysts

• Mouse brain section
• Proliferation of tachyzoites elicits an immune
  response that slows down schizogony, results in
  accumulations of bradyzoites known as zoitocysts
• May persist for years in nervous tissue.

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Sexual Reproduction

• Enteroepithelial cycle in the epithelial lining
  of the cat intestine
• Intestinal epithelial cells infected with oocysts
  (O) and schizonts (S) containing merozoites
• Oocysts in infected epithelial cells and free in
  lumen

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Life Cycle

• Gametogenesis ? fertilization ? oocyst
• Enteroepithelial life cycle (in the cat)
• infective oocyst or zoitocyst ? ingested ?
  sporozoites or merozoites in intestinal lumen ?
  invade cell ? intracellular trophozoite ? mitosis
  ? schizont ? cytokinesis, release from cell ?
  merozoite in lumen ? reinvade cell ? gametocytes
  ? differentiation ? gametes ? fertilization, cyst
  wall formation, release from cell ? oocyst in
  feces ? sporulation (2 to 3 days) ? infective
  oocyst
• Extraintestinal life cycle (other hosts)
• infective oocyst or zoitocyst ? ingested ?
  sporozoites or merozoites in intestinal lumen ?
  invade cells ? intracellular trophozoite ?
  mitosis ? schizont ? cytokinesis, release from
  cell ? tachyzoites ? reinvade cell ?
  intracellular trophozoite ? mitosis ? schizont ?
  host immune response ? zoitocyst containing
  bradyzoites

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Pathogenesis

• Many infections are asymptomatic or mild because
  of the high levels of antibodies in the
  population
• Factors that influence infection
• Virulence of strain T. gondii
• Susceptibility of individual host and host
  species
• Age of the host
• Degree of acquired immunity of host

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Symptoms

• Symptomatic infections can be acute, subacute and
  chronic
• Acute intestine to cats, little consequences
  except to some kittens can infect mesenteric LN
  painful swollen LN in cervical, supraclavicular
  and inguinal areas fever headache muscle pain
  anemia and some lung complications rarely
  causes death
• Subacute pathogenesis continues with more
  extensive in CNS because of lower
  immunocompetence here
• Chronic immunity builds up, decrease
  tachyzoites, production and formation of
  zoitcyst, may remain ntact for years burst
  kills mostly by the immune response but some can
  go on to form new cysts

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Congenital Toxoplasmosis

• Mom to fetus rate of about 45 incidence
• 60 subclinical
• 30 suffer severe cerebral damage
• 9 stillbirth or spontaneous abortion

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Diagnosis and Treatment

• Diagnosis
• Lab tests such as necropsy or biopsy eith
  organism is definitive ELISA or molecular tests
• Treat with pyrimethamine and sulfonamides as
  combinatorial therapy