The first line regimen for primary VL treatment is pentavalent antimonial compounds such as meglumine antimoniate (Glucantime®) and Sodium stibogluconate(Pentostam®) which can be used as a monotherapy (administered as intramuscular injections of 20 mg/ kg/day for 28-30 days) or in combination with cryotherapy or other drugs such as paramomycin (1-3). Other drugs such as amphotericin B deoxycholate, Liposomal amphotericin B (Ambisome®) and miltefosine (administrated orally) may be used for the treatment of VL particularly in patients with clinical or laboratory resistance to pentavalent drugs as well as contraindications caused by these drugs (1).
Until 1990, VL diagnosis was in need of parasitological confirmation including microscopy or culture of the spleen, bone‐marrow, lymph nodes and sometimes peripheral blood specimens. The invasiveness and sometimes fatal complications particularly associated with splenic aspiration brought about the development of simple and accurate serological tests such as DAT (38). Although the IFAT and ELISA are two important serological methods for diagnosis of human VL they require specific materials and equipment (1, 33). The rK39 dipstick is simpler than DAT for screening of human VL particularly in symptomatic cases. The rK39-based tests are easy to perform, quick, cheap and give reproducible results and can therefore be used for early diagnosis of VL at both peripheral and central levels of public health centers Studies comparing the rK39 strip test and DAT found a similar sensitivity (94%) and specificity (89%); however, the DAT showed a slightly higher specificity (39).
On the other hand, rK39 strip tests have certain limitations because anti-Leishmania antibodies can persist for months in patients even after recovery, moreover, it has low specificity in sub-clinical and asymptomatic forms of L.donovani or L.inantum/chagasi infections, particularly among the Sudanese population (18, 33). A recent introduced assay based on the detection of antibodies to the rk28 fusion protein showed a very promising sensitivity and specificity (96% and 98%, respectively) of ELISA to detect anti-Leishmania antibodies in sera among VL patients. In addition, The rK26, A2-ELISA and rKE16 dipstick recombinant antigens from amastigote forms of L.infantum or L.donovani showed desirable results (40-42). Among the available serological tests for the diagnosis of VL, DAT is a simple, highly specific and sensitive, reliable and cost-effective test that can be used in field as well as laboratory studies (43-47). DAT as a semi-quantitative serological test has been used for the serodiagnosis and seroepidemiological studies of VL in both humans and animal reservoir hosts during the last 4 decades. According to our knowledge, this is the second systematic review and meta-analysis about the diagnostic accuracy of DAT for diagnosis of VL. Chappuis et al. included 30 relevant studies that evaluated DAT from January 1986 to December 2004 (11) and reported the pooled sensitivities and specificities of 94.8% and 86%, respectively. In the present study, 24 eligible studies from April 2004 to December 2019 were evaluated using DAT for the diagnosis of VL in immunocompetent patients by the systematic review. Our meta-analysis showed DAT is still a validated serodiagnostic test with high pooled sensitivity of 95% [CI95%,66–100], 97% [CI95%,94–99] and 96% [CI95%, 93–97], respectively while 1:800, 1:1600, and1:3200 cut-off titer were considered. Higher pooled specificity 99% (95% CI, 93–100) was found at a 1:800 cut-off titer.
Specific Leishmania antibodies at a titer of 1:800 showed VL infection (33) whereas Leishmania antibodies at a titer of 1:3200 with pathogonomonic clinical signs such as hepatosplenomegaly, dromedary fever, anemia and progress weakness reflected active VL (43).
The high diagnostic accuracy of DAT using different samples including serum, plasma or even urine samples has been reported (11, 48).
According to the of the previous meta-analysis comparing the diagnostic accuracy of DAT and rK39 strip test, DAT showed 1% more sensitivity and 2% more specificity than rK39 strip test.
Although we did not have sufficient information regarding human immunodeficiency viruses status of the cases, it has been reported that DAT has an acceptable sensitivity in the diagnosis of VL in HIV-positive patients (49). Although sensitivity of DAT in the majority of studies was more than 90% some heterogeneity in the sensitivity of the tests might be related to the geographical location of the study, differences in antibody concentrations, and immune or nutritional status of the patient (50). In the current study, it was not possible to evaluate the test performance according to these factors.
Although early diagnosis and appropriate treatment is crucial for controling of the anthroponotic form of VL (i.e. Indian and African forms of VL), control of zoonotic VL is highly difficult and the current control strategies for zoonotic VL rely on animal reservoir hosts and phlebotomine vectors (1), the use of insecticide-impregnated materials to prevent insect bites, and active case detection with appropriate treatment to decrease the mortally rate of VL (45).
VL is highly fatal in the absence of appropriate anti-Leishmania drugs. Although pentavalent antimonial compounds are introduced as the drugs of choice for the treatment of VL, intramuscular or painful intravenous injections with high toxicity and high price consider. However, anti-leishmanial drugs are usually expensive and have significant toxicity. Since the clinical manifestations of VL have low specificity and are not completely pathognomonic, performing of confirmatory tests to recognize the VL patients needing treatment are highly required. These tests must not only be sensitive, but they also need to be specific because the current anti-Leishmania drugs prescribed to treat VL are highly toxic (7).
The most important limitation for the evaluation of serological tests is the absence of an appropriate gold standard test. Confirmation of VL depends on the finding of Leishman bodies of Leishmania sp. in samples prepared from bone marrow or spleen, lymph nodes and liver. This procedure is highly invasive, and it should be performed only in suspected cases of VL. Furthermore, the sensitivity of this method is diverse (47).
In some VL-endemic areas, DAT is used regularly for the diagnosis and sero-epidemiological studies of VL because it is simple due to its high sensitivity (33, 44).
The performance of DAT is neither Leishmania species-specific nor region dependent (6, 43).
Major limitations of DAT are its long incubation period to report, batch to batch variability of the antigen and cross-reactivity with Trypanosoma cruzi infection (43, 44). DAT titers decline over time below the cut off (1:800), while itstill remain positive for a relatively long time (up to 5 years in more than 50% of VL cases) after the cure. Therefore, performing of this test for treatment follow up or for the diagnosis of disease relapse is not recommended (49). To overcome the problem of long incubation time, a fast agglutination screening test (FAST) has been introduced, which uses only one serum dilution and requires only three hours of incubation (51). FAST for the detection of L. infantum infection was compared with the conventional DAT in Iran indicating a sensitivity of 95.4% and specificity of 88.5% for fast DAT in comparison with conventional DAT (51).
Our study has some limitations. First, we compared pooled estimates between different published studies. So, the possibility of confounding should not be ignored. Second, the study used the data provided by published literature, and some data including sex and age for the included patients was unavailable and made subgroup analysis difficult.