Evaluation of Cystatin-Capture and Periodate-Treated ELISA in Serodiagnosis of Toxoplasmosis and Hydatidosis

Abstract

Toxoplasma gondii is an obligate intracellular parasite that can invade and replicate within any nucleated cell of vertebrate hosts, including humans. As an opportunistic human pathogen, T. gondii causes devastating disease in immunocompromised individuals, especially AIDS patients and congenitally infected neonates (Black and Boothroyd, 2000).

Echinococcus granulosus is the causative agent of cystic hydatid disease, a disease of a global distribution. Although, the liver is the most frequently involved site, the cysts can develop in almost all organs of the body. Main clinical symptoms in humans include liver dysfunction, lung problems, ascites, abdominal pain, hepatomegaly, splenomegaly and central nervous system disorders. Because there is not any production of the parasite into faeces, the laboratory diagnosis of hydatidosis mainly rests upon the detection of anti-hydatid antibodies in serum samples as well as clinical and radiological data (Markell and Voge, 1999).

Enzyme linked immunosorbent assay [ELISA] has been applied to the seroimmunodiagnosis of many parasitic diseases, because of its requirement for low amounts of antigens, and simplicity. One of the major obstacles encountered in the evaluation ELISA is the false-positive results due to immunological cross-reactions with other parasitic diseases which exhibit some lack of specificity (Poretti et al 1999).

The aim of the present study is to comparatively assess the diagnostic performance of three different ELISA tests, cystatin capture ELISA, SMP-ELISA and conventional ELISA to detect anti-Toxoplasma IgG antibodies and anti-Echinococcus IgG antibodies in the serum , aiming to increase the diagnostic efficacy of ELISA technique in detection of hydatid disease and toxoplasmosis.

Thirty patients with toxoplasmosis, 30 patients with hydatidosis, 10 patients with other parasitic diseases [amoebiasis (2 cases), fascioliasis (2 cases), schistosomiasis (3 cases), toxoplasmosis (3 cases) - used with hydatid ELISAs - and hydatidosis (3 cases) - used with Toxoplasma ELISAs] and 10 normal persons as control group were included in this study. All cases were attending the Diagnostic and Research Unit – Parasitology Department – Faculty of Medicine – Ain Shams University.

The results showed that on using conventional ELISA in diagnosis of toxoplasmosis, 28 out of 30 sera of toxoplasmosis patients (Group I) gave positive reaction. Two out of 10 sera of patients infected with other parasites (Group IIIA), one serum of amoebiasis and one serum of bilharziasis gave positive results. All sera of normal control (Group IIIB) gave negative results. This indicates a sensitivity of 93.3%, a specificity of 90%, positive predictive value (PPV) of 93.3% and negative predictive value (NPV) of 90%.