Notes from Egyptian Toxoplasmosis Lecture:
7th International conference of the Egyptian Society for Infection Control;
Plenary Lecture : Back
Cats shed oocyst for 3 weeks (i.e. only once in the lifetime of each cat)..
They release 10M oocysts per day.
These become infective after 3 days
(embryonation outside the host in the faeces).
Hence approximately 200M oocysts are released per cat.
In each oocyst contains two sporocysts each with four sporozoites.
As a result there are tissue cysts in
Pig meat, in brain, heart and skeletal muscle.
Tissue cysts persist indefinately.
Infection is a result of direct contamination from cat faeces
but also from:
eating tissue cysts
and, very rarely, can also result from:
Blood, Milk and Saliva.
Infection of a foetus comes from tachyzoites
crossing the placenta before infecting the fetus
Neural tissue is the commonest site affected.
Women infected before pregnancy are immune
and the organism will not be transmitted to the fetus
except in rare circumstances where the mother is
immunocompromised and reactivation occurs
Congenital infection is the result.
The clinical picture is usually asymptomatic in the mother.
If infection occurs early in pregnancy then the result is abortion.
Neural damage is most serious to the infant
if the infection occurs in the first trimester as:
Congenital toxoplasmosis recognizable as
2. intracerebral calcification
4. mental subnormality
N.B. Approx 9% die from the infection
The majority of infants will appear normal at birth
and signs may occur after a few months
or not be apparent for many years.
Affected chilren may present with
mental retardation, deafness,
spacticity, jaundice, fever,
hepatsplenomegaly, diarrhoea etc.
Seroepidemiological surveys have demonstrated
widespread infection throughout the world
although incidence varies:
e.g.50% England by 60 years of age.
2-2.5 per 1000 pregnancies.
The incidence in pregnancy can be predicted
if the risk of transmission of infection to the fetus is known.
Determined as between 33 and 44%.
Major brain damage cab be detected by CAT scans
(without ventricular dilation).
and there is enlargement of the right liver lobe.
Ascites is common and can be used in monitoring the effect of antibiotic
1. Specific IgM
2. Cultureof fetal blood and fibroblasts.
3. DNA probes and Polymerase Chain reaction (PCR).
4. ELISA 'avidity reaction'
( conducted with Urea in the buffer).
Detects potent imminty in a current infection
c.f. the long lasting immune response of previous exposure
Prevent transmission in pregnancy where thre has been exposure
Spiramycin to the mother prevents transmission if given soon enough.
Minimises damage where the mother refuses termination.
FolinicAcid (Alternation within a 3 weeek course).
Also Spiramycin may be allowed throughout pregnancy.
Avoidance of infection
Pregnant women are advised:
1. Not to empty cat litter trays, which should be disinfected daily with boiling water.
2. Not to eat undercooked meat
Advice to women who have experienced infection
That this is not a cause of habitual abortion