Toxoplasma gondii and toxoplasmosis

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Toxoplasma gondii and toxoplasmosis

• Cheng Yanbin April 2005

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Toxoplasma gondii

• Infects most species of warm blooded
  animals,including humans.
• Cause the disease toxoplasmosis.
• Found in almost every country.
• Estimated to infect 50 of the population of some
  countries.
• Most of infections are asymptomatic.

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Morphology I

• Trophozoite (tachyzoite bradyzoite)
• banana form or crescent-shape, 47 µm by 24
  µm. (Pseuocyst)
• Cyst spherical, has a think wall around the
  masses of bradyzoites.

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Morphology II

• Mature oocyst contains two sporocysts that
  contains 4 sporozoites.

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Life cycle

• Cats are the final host
• Mammals, birds and humans are the intermediate
  host
• The common infectious stages
• A) The tachyzoites (in groups or clones)
• B) The bradyzoites (in tissue cysts)
• C) The sporozoites (in oocysts) .

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Life cycle

• Human infection may be acquired in several ways
• A) ingestion of undercooked infected meats
  containing Toxoplasma cysts
• B) ingestion of the oocyst from fecally
  contaminated hands or food
• C) organ transplantation or blood transfusion
• D) transplacental transmission
• E) accidental inoculation of tachyzoites

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Life cycle

• In the human body, the actively proliferating
  trophozoites or tachyzoites are usually seen in
  the early, more acute phages of the infection.
  The cysts are formed in chronic infections and
  are found primarily in muscle, brain and other
  organs. It is a result of the host immune
  response.

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Clinical diseases

• The majority of infections are no-symptoms. The
  most severe symptoms are seen with congenital,
  transpacental infections or infections in the
  compromised patients.
• Mechanism When the trophozoites are actively
  proliferating, they invade adjacent cells from
  the original infected cells as it ruptures. This
  process create s focal lesions. The organisms can
  be disseminated via the lymphatic liquid and the
  blood stream to other tissues.

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Congenial infections

• It may be particularly severe if the mother
  acquires the infection during the first or second
  trimester of pregnancy.
• Symptoms in these infants may include
  retinochoroiditis, cerebral calcification,
  hydrocephalus or microcephaly. Symptoms of CNS
  involvement may not appear until several years
  later.
• Asymptomatic congenital infections were common in
  prospective studies.

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Acquired infections

• In 90 of cases, no clinical symptoms are seen
  during the acute infection.
• However, rare symptoms seen in acquired acute
  infections would include chorioretinitis,
  myositis, and symptomatic heart, lung, liver, or
  CNS involvement.
• Infections acquired can be categorized into four
  groups

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• Lymphadenitis, fever, headache, and myalgia, with
  a possibility of spenomegaly.
• Typhus-like exanthemous form with myocarditis,
  meningoencephalitis, atypical pneumonia, and
  possibly death
• CNS involvement, which is usually fatal
• Retinochoroiditis, which may be severe, requiring
  enucleation.
• The most common manifestation in adults is local
  or generalized lymphadenopathy, and the nodes
  most commonly involved are those of the neck.

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Infections in the immunocompromised patients

• Infections in the compromised patients can lead
  to severe complications (Hodgkins disease, non-
  Hodgkins lymphomas, leukemias, solid tumors,
  AIDS and transplant recipients).
• The CNS is primarily involved, with diffuse
  encephalopathy, meningoencephalitis or cerebral
  mass lesions

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Laboratory diagnosis

• Observation of T.g in patient specimens, such as
  bronchoalveolar lavage material, or lymph node
  biopsy.
• Isolation of T.g from blood or other body fluids,
  by intraperitoneal into mice or tissue culture.
• Serological tests using killed antigens.
• Detection of T.g DNA by PCR.

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Treatment

• Treatment is not needed for a healthy person who
  is not pregnant.
• Treatment may be recommended for pregnant women
  or persons who have weakened immune systems.
• Oral administration of pyrimethamine, usually
  accompanied by sulfadiazine, is the treatment of
  choice at this time.