Toxoplasmosis Flashcards
Toxoplasmosis - Incidence
2:1 000 pregnancies
Transmission
Transmission and risk of abnormalities rate in each trimester
The parasite Toxoplasma gondii is transmitted to humans through uncooked meat (esp pork, mutton and wild game) and inadverted ingestion of oocytes in cat faeces (contact with cat litter, soil, unwashed fruit and vegetables) -Transplacental transmission occurs through primary infection Infection prior to pregnancy makes congenitial infection very unlikely Transmission T1 low 4-15% T2 int 25-45% T3 high 30-75% Risk T1 high 35-85% T2 int 20-30% T3 low 5-20%
Incubation
Up to 23 days, IgG and IgM antibodies appear within 1-2 weeks of infection
Clinical presentation
90 % asymptomatic, glandular fever like illness, OE - lymphadenopathy
Rarely immunocompromised mothers can get disseminate infection and encephalopathy
Work up if maternal infection confirmed
T Gondi PCR on amniotic fluid 18-20/40 or more then 4 weeks post maternal inf
USS +/- fetal MRI - generalised calcifications
USS to assess for anatomical abnormalities eg microcephaly or hydrocephaly, intracerebral calcification and hydrops fetalis + ongoing growth / monitor for microcephaly and ventricular dilatation
Treatment
Maternal infection T1- Treat with Spiramycin to reduce infection to the fetus
- if fetal infection (confirmed PCR from amnio) can treat with
pyrimethamine 25 mg BD, (folate antagonist - dose related bone marrow suppression anaemia, leukopenia and thrombocytopenia)
sulfadiazine 1 g TDS, (folic acid antagonist)
and folinic acid (prevent bone marrow suppression)
alternating with spiramycin although there is associated risk of teratogenicity and bone marrow toxicity to mum and baby
Can also use spiramycin and cotrimoxazole from 14 weeks
Or azithromycin 500mg daily and pyrimethamine
Termination can be offered if appropriate
FBC weekly
Prevention
Avoid undercooked or raw meat, unpasteurised milk, wash fruit and vegetable, wear gloves then gardening, avoid contract with cat faeces
Maternal and fetal sequelae
Maternal risks
Severe disseminated disease, chorioretinitis, encephalitis esp. in immunocompromised patients
Fetal risks
Congential chorioretinits, microcephaly, hydrocephaly, intracerebral calcification, mental retardation
IUD IUGR
Classic triad is Chorioretinitis, hydrocephalus and intracerebral calcifications
What is the value in testing toxo IgM and IgG antibodies
IgG peak within 1-2 months of infection, then decline but usually persist for life
IgM lasts 10-13 weeks
If blood is saved from booking bloods can look back and compare the presence of IgG then
Diagnosis of infection if IgM positive and IgG negative or greater then 4 fold rise in IgG over 2 samples more then 3 weeks apart
IgM and IgG + = infection within 6 months
Can assess IgG avidity
IgG low aviddity infection within 12 weeks
IgG high avidity infection older then 12 weeks
IgG + IgM negative = infection over 2 years ago
False positive IgM can be from rheumatoid factor or antinuclear antibodies
How to investigate the infected neonate
Management of infant:
• Ophthalmologist/auditory/neurology review before discharge
• Radiology: Head USS/MRI
• Laboratory: Serology: IgM at birth; IgG persists >6months.
PCR blood/CSF/placenta
• Paediatrician referral and ongoing review
• Treatment for one year
What are the fetal affects
Chorioretinitis Hydrocephalis Intracranial calcification (diffuse) Ventriculomegly Intellectual disability Hepatosplenomegly
How to prevent infection
- Prevention is based on avoiding sources of infection:
- Handwashing
- Gloves in the garden and gloves to clean kitty litter
- Cooking meat well: meat should be cooked to 66C or frozen for 24 hours at less than -12C
- Washing salad leaves and vegetables
- Avoid travel to less developed countries with more virulent parasite strain
