Page 64 - Medical Parasitology_ A Textbook ( PDFDrive )

Toxoplasma gondii 57

• Latex agglutination test
• Sabin Feldman dye test (Gold standard). This is not carried out as a routine
test because it involves use of live zoites which are maintained in culture.

IgM appears first about 1–2 weeks after infection. It peaks at about 8 weeks. IgG
appears after IgM, typically reaching maximal levels at about 4 months, then
declines to a lower level over the next 12–24 months. IgG persists for decades.
Toxoplasma IgG avidity testing was developed to help discriminate between
past and recently acquired infections. High avidity IgG antibodies indicate past
infection. Low avidity IgG antibodies indicate recent infection. This test is useful
in pregnancy to establish timing of the infection for management of the
pregnancy.

2. Molecular diagnosis
PCR on blood, CSF or amniotic fluid samples.
3. Microscopic examination
Giemsa-stained impression smears of lymph nodes, bone marrow, spleen or
brain may occasionally show the trophozoites. Tissue sections may show the cyst
form.
4. Animal inoculation and cell cultures
5. CT scan
To detect lesions in the brain.

Treatment

Only symptomatic cases are treated. Combination drugs of choice are pyrimeth-
amine (25–50 mg daily for 1 month) and sulfadiazine (2–6 g daily for 1 month) with
folinic acid to prevent bone marrow suppression. Pyrimethamine is teratogenic.
Pregnant mother in first trimester can be given spiramycin in replacement of pyri-
methamine. For congenital toxoplasmosis, daily oral pyrimethamine and sulfadia-
zine with folinic acid are given for 1 year. Systemic corticosteroid may be added to
reduce chorioretinitis.
Patients with ocular toxoplasmosis are treated for 1 month with pyrimethamine
plus either sulfadiazine or clindamycin.
AIDS patients who are seropositive for T. gondii and have a CD4+ T
lymphocyte count below <100/μL, should receive primary prophylaxis against
toxoplasmic encephalitis. Trimethoprim -sulfamethoxazole (Bactrim) (160 mg
trimethoprim; 800 mg sulfamethoxazole orally once daily) is the drug of choice.
If trimetho prim -sulfamethoxazole cannot be tolerated by patients, dapsone -
pyrimethamine is the recommended alternative drug of choice. Prophylaxis
against toxoplasmic encephalitis should be discontinued in patients who have
responded to anti-retroviral therapy (ART) and whose CD4+ T lymphocyte count
is above 200/μL for 3 months.