infectious diseases
Toxoplasmosis
Diagnosis of Toxoplasmosis
Serologic testing For central nervous system involvement, CT or MRI and lumbar puncture Histopathologic evaluation of biopsies Polymerase chain reaction–based assays of blood, cerebrospinal fluid, tissue, or, during pregnancy, amniotic fluid Toxoplasmosis is usually diagnosed serologically using an indirect fluorescent antibody (IFA) test or enzyme immunoassay (EIA) for IgG and IgM antibodies (see table). Specific IgM antibodies appear during the first 2 weeks of acute illness, peak within 4 to 8 weeks, and eventually become undetectable, but they may be present for as long as 18 months after acute infection. IgG antibodies arise more slowly, peak in 1 to 2 months, and may remain high and stable for months to years. Assays forToxoplasmaIgM lack specificity. The diagnosis of acute toxoplasmosis during pregnancy and in the fetus or neonate can be difficult, and consultation with an expert is recommended. If the patient is pregnant and IgG and IgM are positive, an IgG avidity test should be done. High avidity antibodies in the first 12 to 16 weeks of pregnancy essentially rules out an infection acquired during gestation. But a low IgG avidity result cannot be interpreted as indicating recent infection because some patients have persistent low IgG avidity for many months after infection. Suspected recent infection in a pregnant woman should be confirmed before intervention by having samples tested at a toxoplasmosis reference laboratory. If the patient has clinical illness compatible with toxoplasmosis but the IgG titer is low, a follow-up titer 2 to 3 weeks later should show an increase in antibody titer if the illness is due to acute toxoplasmosis, unless the host is severely immunocompromised. In general, detection of specific IgM antibody in neonates suggests congenital infection. Maternal IgG crosses the placenta, but IgM does not. Detection ofToxoplasma-specific IgA antibodies is more sensitive than IgM in congenitally infected infants, but it is available only at special reference facilities (eg, Toxoplasma Serology Laboratory, Palo Alto Research Institute, Palo Alto, CA). An expert should be consulted when fetal or congenital infection is suspected. must be distinguished from other intracellular organisms, such as Histoplasmosis , If central nervous system (CNS) toxoplasmosis is suspected, patients should have head CT with contrast or MRI with contrast, or both plus a Lumbar Puncture (Spinal Tap) if there are no signs of increased intracranial pressure. MRI is more sensitive than CT. MRI and CT with contrast typically show single or multiple rounded, ring-enhancing lesions. Although these lesions are not pathognomonic, their presence in patients with AIDS and CNS symptoms warrants a trial of chemotherapy for Acute infection should be suspected in immunocompromised patients if the IgG is positive. However, IgG antibody levels in AIDS patients withToxoplasmaencephalitis are usually low to moderate, and IgG antibodies are sometimes absent; IgM antibodies are not present. If the suspected diagnosis of CNS toxoplasmosis is correct, clinical and radiographic improvement should become evident within 7 to 14 days. If symptoms worsen over the 1st week or do not lessen by the end of the 2nd week, a brain biopsy should be considered. Ocular disease is diagnosed based on the appearance of the lesions in the eye, symptoms, course of disease, and results of serologic testing. 