Toxoplasmosis

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Toxoplasmosis

• Agent Toxoplasma gondii
• Common parasitic infection of humans and animals
• Infects most speciesworldwide distribution

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Toxoplasmosis

• Classification
• Protozoan parasite
• Coccidian-like
• Intracellular
• Name derived from
• Genus crescent shaped tachyzoite (toxonbow
  plasmaform)
• Species first isolated from a rodent
  (Ctenodactylus gundi)

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Toxoplasmosis

• Characteristics of organism
• Three infective stages
• Tachyzoites rapid growth
• Bradyzoites tissue cyst form, slow growth
• Sphorozoites oocysts
• Unsporulated
• Sporulated
• Capable of growth and replication in a variety of
  host cells

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Toxoplasmosis

• Characteristics of organism
• In macrophages capable of evading immune
  mechanisms
• Ability to survive (evading digestion by
  macrophage) may be due to prevention of lysomal
  fusion with phagocytic vacuole
• Reproduction (sexual) occurs only in cats -
  multiplication by cell division occurs in most
  host cell types

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Toxoplasmosis

• Epidemiology
• Occurrence ubiquitous worldwide
• Humans
• Seroprevalence in humans estimated to be
  500,000,000
• Congenital infection lt0.1
• Animals
• Widespread infection due to prolific oocyst
  shedding
• At any given time, small numbers (1) of cats
  (primarily domestic) may be shedding oocysts

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Toxoplasmosis

• Epidemiology
• Reservoir
• Felids, primarily domestic but numerous wild
  felids shed oocysts and may be responsible for
  infection in some settings
• Transmission (to humans)
• Transplacental tachyzooites
• Orally oocysts by hand to mouth, undercooked
  meat with tissue cysts contaminated food or
  water
• Inhalation rare
• Infected tissue (blood, transplantation)

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Toxoplasmosis

• Epidemiology
• Life cycle
• Cats acquire infection by eating any of three
  infective stages in infected prey (rodents or
  birds)
• Intraintestinal cycle occurs only in cats
• Multiply in wall of small intestine, produce
  oocysts
• Oocysts shed in great numbers for 2-3 days
• Oocysts sporulate within wihtin 5 days
• Sporulated oocyts highly resistant
• Healthy cats shed during acute stage, but not
  after (at least in sufficient numbers to be
  infective)
• Congenital infections may occur in sheep and
  goats (and humans), but uncommon in cats

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Toxoplasmosis

• Epidemiology
• Life cycle
• Extraintestinal cycle occurs in cats and
  intermediate hosts (including humans)
• cyst from intraintestinal cycle penetrate deep
  into intestinal wall
• multiply as tachyzoites, spread to other body
  sites
• Immune system finally restrains infection,
  leading to dormant stage (cyst) in muscle or
  brain

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Toxoplasmosis






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Toxoplasmosis

• Clinical features
• Cats
• usually asymptomatic
• Occasionally younger animals or immunocompromised
  animals (FIV or FeLV) show non-specific signs
  (fever, lethargy, inappetance) followed by
• pneumonia (mainfested by respiratory distress
  with gradual increasing severity)
• Hepatitis - jaundice, vomiting, diarrhea
• CNS seizures, hyperesthesia, ocular
  inflammation leading to blindness

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Toxoplasmosis

• Clinical features
• Humans
• Normal hosts
• Incubation period 10-14 days
• 80 asymptomatic
• Localized infection manifested as lymphadenopathy
  resolving spontaneously (wks to months)
• Some may experience fever, myalgia, headache
• Rash, hepatitis - rare

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Toxoplasmosis

• Clinical features
• Humans
• Immunocompromised host (reactivation disease)
• Encephalitis most common manifestation
• Present with sever headache, altered mental
  status, seizure, neurological deficits, pneumonia
  (ARDS), and myocarditis
• Estimated up to 40,000 cases in AIDS patients in
  US in 1981
• Most common cause of AIDS encephalitis in US

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Toxoplasmosis

• Clinical features
• Humans
• Congenital infection
• Occurs when women becomes infected during
  pregnancy or with reactivation (if
  immunocompromised)
• Most severe when occurs in first trimester
• Varying signs
• Ocular impaired vision to blindness due to
  chorioretinitis, microophthalmia
• CNS hydrocephalus, seizures, microencephaly

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Toxoplasmosis

• Diagnosis
• Serology
• Sabin-Feldman test most reliable for antibody
  detection
• Disdavantage expensive, uses live tachyzoites
• IFA uses killed tachyzoites
• Others - ELISA, IHA
• Histology
• Direct examination of cycts of trophozoites in
  tissue
• Tachyzoites in blood confirm active infection
• Cysts in placenta confirms congenital infection
• Geimsa stain of impression smear - useful in
  immunosuppressed patients since Ab response low

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Toxoplasmosis

• Tachyzoites from bronchial lavage specimen

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Toxoplasmosis

• Tachyzoites (arrows)

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Toxoplasmosis

• Tachyzoites in tissue (feline)

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Toxoplasmosis

• Bradyzoites (within zoitocyst) in cardiac muscle

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Toxoplasmosis

• Sporozoites (in oocyst) from fecal specimen (cat)

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Note Oocyst contains two sporocysts, each
containing four sporozoites


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Toxoplasmosis

• Treatment
• Multi-drug therapy pyrimethamine plus
  trisulfapyrimidines (or sulfadiazine) and folinic
  acid
• Treatment in pregnancy controversial
• 4 - 6 weeks after cessation of signs in
  immunocompromised patients first year of life in
  infants
• Spiramycin used in Europe safe and effective
  in pregnancy

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Toxoplasmosis

• Prevention and control
• Thorough washing of hands after handling meat
• Wear protective gloves when handling litter,
  gardening, childrens sand boxes
• Testing pregnant women for antibodies (?)

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