Evaluation of conventional & serological methods for rapid diagnosis of cryptococcosis.

BACKGROUND & OBJECTIVE: Cryptococcosis is a chronic infective condition affecting the central nervous system. Unless diagnosed early and specific treatment instituted it can be fatal. There is an urgent need for a rapid and specific diagnostic tool for better management of the patients. Conventional methods such as culture and India ink are specific but cumbersome and time consuming. Serological methods of detection are rapid but have problems of false positivity and cross-reactivity with other micro-organisms. We carried out this study to compare and evaluate the conventional methods with serological methods of detection of cryptococcal meningitis. METHODS: A comparative evaluation of conventional methods (India ink and culture) with LAT (latex agglutination test) and EIA (enzyme immunoassay) was done in 127 CSF samples using culture and EIA as reference separately. RESULTS: India ink was positive for Cryptococcus in 72.4 per cent of the samples; 56 per cent were culture positive; LAT positive were 85 per cent and 79.5 per cent were positive by EIA. When culture was positive, all other tests were in agreement to it. However, when culture was negative there was significant difference between the pair of discordance of various diagnostic tests. Culture was 83.46 per cent in agreement to India ink, 76.3 per cent to EIA and 70.8 per cent to LAT. EIA was 92.9 per cent in agreement to India ink and LAT; 6.3 per cent showed false positive by LAT. INTERPRETATION & CONCLUSION: EIA is valuable in establishing diagnosis when culture is negative for cryptococcosis. EIA is more specific and has potential advantages over LAT as it gives clear discrimination of positive from negative results. Thus, EIA may be used as a simple, rapid, and reliable serological test for early detection of cryptococcal antigen in clinical samples like CSF in routine laboratories.

monoclonal antibody-based latex agglutination test for detection of circulating schistosomal antigens in human schistosomiasis maizsoni

Schistosomiasis is a major public health problem with a worldwide distribution, Diagnosis of this disease by simple and rapid immunoassays is a priority. The objective of the present study was to standardize and evaluate the latex agglutination test [LAT] as a simple test for the detection of circulating schistosomal antigen [CSA] in serum and urine samples of S. mansoni patients and compare it with ELISA. According to stool examination this study included, 52 S. mansoni infected patients, 20 other parasites infected patients and 20 negative control samples. A polystyrene latex [0.81 micro m] suspension was used as a carrier particle for anti-S. mansoni adult worm tegumental antigen monoclonal antibody [l2D/10F] in the test. The Latex particles sensitized with MAb were used for the detection of CSA in urine and serum samples. The sensitivity of LAT assay was 88.5% in urine and 86.6% in sera versus 90, 4% and 92.3% for ELISA. The specificity of LAT assay was 90% and 95% for urine and sera versus 85% and 95% for ELISA. The diagnostic efficacy of EAT was 89.1% and 90.2b for urine and serum samples, respectively versus 88% and 93.5% for ELISA. Moreover, a positive correlation was found between ova count in stool of S. mansoni infected patients and both the intensity of LAT and OD readings of ELISA in urine [r= 0.922; p< 0.001 and r= 0.865; p< 0.001, respectively] and in serum [r=0.847; p< 0.001 and r= 0.781; p< 0.001, respectively]. In conclusion, LAT is a suitable applicable diagnostic method in field survey especially when followed by ELISA as a confirmatory test in query false negative results. In the same time, more trials are required to increase the sensitivity and specificity of LAT to allow its use on a large scale in field surveys and as diagnostic kits for multiple parasitic infections