Life cycle of Toxoplasma gondii
ENTERIC-EPITHELIAL CYCLE in definitive host (cat only)
Unsporulated oocyst (non-infective form)
Sporulated (infective fo
Merozoites
Macrogamete
1–5 days
The oocyst sporulates in the external environment
Non-infective oocysts are excreted in faeces
Zygote
Sporozoites
Microgamete
Meront
Small intestine cells
Carnivores become inf
Schizont
Cat ingests tissue cysts with bradyzoites - new oocysts in 3–10 days Cat ingests oocysts - oocysts in 19–48 days
Sporulated oocysts (1-5 days)
D.H. Cat
Unsporulated
oocysts in faeces
D.H. = definitive host I.H. = intermediate host
Life cycle from Beugnet, F., et al (2018) Textbook of Clinical Parasitology in Dogs and Cat. Grupo Asis Biomedica, S.L.; Adapted from Carithers, D., et al (2012) Pet Owner Educational Atlas.
IN HUMANS
PREVALENCE AND RISK FACTORS • It is estimated globally that approximately 25-30% of the population is infected by Toxoplasma , however significant geographical variation is seen, relating to climatic factors (higher prevalence in cool, humid conditions), anthropogenic factors (dietary habits) and socioeconomic factors (higher prevalence in resource-poor communities). 10 • Whilst primary infection during pregnancy is considered rare in Australia, infection in the Australian population is relatively common, with most studies reporting a seroprevalence of between 20 and 40%. 11,12 A recent pilot study in Busselton, Western Australia, reported a seroprevalence of 66%, 13 which, if representative of the country as a whole, would be counter to the situation in many other developed countries in which Toxoplasma infection has declined over time. 10
Photomicrograph of brain tissue sample from a patient with neurotoxoplasmosis. Several cysts containing Toxoplasma gondii bradyzoites are visible in the image (Public Health Image Library, CDC)
CONTENTS
90 Companion Animal Zoonoses Guidelines
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