Evaluation of the direct agglutination test and the rK39 dipstick test for the sero-diagnosis of visceral leishmaniasis

Abstract

The direct agglutination test (DAT) based on a freeze-dried antigen and the rK39 dipstick test were evaluated for the sero-diagnosis of visceral leishmaniasis (VL). The sensitivity and specificity of both tests were determined using sera from confirmed VL patients (n = 21), healthy controls (n = 19) and from patients with other confirmed infectious diseases (n = 42). The DAT had a sensitivity and a specificity of 100%. The rK39 had a sensitivity of 85.7% and a specificity of 82%. Both tests were also used to screen blood samples of confirmed VL patients (n = 15) Visceral leishmaniasis (VL or kala-azar) is the most severe form of leishmaniasis. Approximately 500,000 new cases of human VL occur annually and the disease is mainly found in Brazil, East Africa and on the Indian subcontinent. American visceral leishmaniasis (AVL), caused by Leishmania chagasi, is a major health problem in many parts of Brazil. Traditionally, the disease was confined to rural and peri-urban areas, but in the last few years the number of human cases of AVL in metropolitan regions is dramatically increasing (Silva et al. 2001). It is important to diagnose AVL as early as possible, because the disease is in most cases fatal if left untreated. The principal clinical symptoms of AVL are an enlarged spleen and a prolonged irregular fever (WHO 1996). Other signs and symptoms are loss of weight, pallor, enlarged liver, enlarged lymph nodes, anaemia, cough and diarrhoea. These signs and symptoms may mimic those of malaria, typhoid, tuberculosis, schistosomiasis and other diseases. The clinical suspicion may be confirmed directly by the detection of parasites in patient material or by culture. However, sample retrieval is inconvenient for the patient and parasite isolation by culture is time-consuming, expensive and difficult.Because of the above-mentioned limitations of direct diagnostic methods, a number of indirect immunological tests have been developed. These tests should meet several prerequisites in order to be of practical use. They should be sensitive and specific, cheap (in particular for use in developing countries) and easy to perform under harsh field conditions (Veeken 1999). The direct agglutination test (DAT) remains the first line diagnostic tool in many developing countries as it is a simple test with a high sensitivity, specificity and reproducibility, easyto-perform and not requiring specialised equipment (Zijlstra et al. 1991, Boelaert et al. 1999a,b, Schallig et al. 2001. The introduction of a freeze-dried antigen makes the DAT very suitable for use under remote field conditions as a cold chain for storage of antigen is not required (Meredith et al. 1995, Zijlstra et al. 1997, Schallig et al. 2001. A limitation of the DAT is the relatively long incubation time (18 h) and the fact that serial dilutions of blood or serum must be made. A dipstick, rK39 dipstick, based on the cloned antigen of a 39 amino acid repeat that is part of a 230 kDa protein encoded by a kinesin-like gene of L. chagasi (Burns et al. 1993), may circu...

Performance of a rapid diagnostic test for the detection of visceral leishmaniasis in a large urban setting

“…In Brazil, validation studies of the IT-LEISH TM have reported a sensitivity varying from 93% to 100% and a specifi city between 94% and 96% 18,20 , considering confi rmed cases only as those with a parasitological diagnosis. In addition, the PPV and NPV of 98% and 89%, respectively, were similar to those found in our study.…”

“…In addition, the PPV and NPV of 98% and 89%, respectively, were similar to those found in our study. Evaluations of the performance of Kalazar Detect TM have shown sensitivity values between 85.7% and 90% and a specifi city between 82% and 100% 18,19 .…”

“…In addition, a meta-analysis of 13 studies reported an overall sensitivity and specifi city of 93.9% and 90.6%, respectively 15 . In Brazil, estimates of the sensitivity and specifi city of RDTs vary between 85.7 and 100% and 82.0 and 100%, respectively [17][18][19][20][21] , but few studies have been conducted in real-world scenarios. For example, among immunocompromised patients, the sensitivity of RDTs seems to be lower, with one study reporting an estimation of 77.3% 16 .…”

Specificity of the rapid rK39 antigen-based immunochromatographic test Kalazar Detect(r) in patients with cutaneous leishmaniasis in Brazil

“…These tests are fast and easy to perform and the results are available in less than 20 min on average (Boelaert et al 2007). Studies on rapid tests for VL have found sensitivity and specificity values that range from 67-100% and 59-100%, respectively (Schallig et al 2002, Carvalho et al 2003. However, there are variations among geographic regions and commercially available tests (WHO 2011).…”

“…However, there are variations among geographic regions and commercially available tests (WHO 2011). Studies have reported false positives when using the rK39 antigen due to cross-reactivity with other protozoans (Schallig et al 2002, Sundar et al 2002. A meta-analysis that involved 13 research centres that used the rK39 rapid test for the diagnosis of VL yielded average sensitivity and specificity values of 93.9% and 90.6%, respectively (Chappuis et al 2006).…”