Rapid detection of human Leishmania infantum infection: a comparative field study using the fast agglutination screening test and the direct agglutination test

Some zoonotic infectious diseases are prevalent among children under 15 years of age in Ardabil Province, northern Iran

BACKGROUND

This study sought to investigate the seroprevalence of visceral leishmaniasis (VL), toxocariasis, brucellosis, and salmonellosis, as well as their co-infection and potential cross-reaction, in children under 15 years referred to health centers in Ardabil province, Iran, from 2019 to 2021.

METHODS

The current study examined 1,550 serum samples using direct agglutination test (DAT), Toxocara canis ELISA, Wright, and Widal tests to detect antibodies against Leishmania, Toxocara, Brucella, and Salmonella, respectively. We also compared the test results to determine the possibility of cross-reactivity or simultaneous seropositivity in the tested samples.

RESULTS

In general, anti-Leishmania antibodies were positive in 78 samples (5%) at titers of ≥ 1:800, while only 8 cases had titers of ≥ 1:3200, which was considered as positive result. Therefore, the seroprevalence of VL was estimated to be at 5.16 per 1,000 at-risk populations. Meshkin-Shahr city had the highest seroprevalence (7 cases, 87.5%), followed by Ardabil (1 case, 12.5%) (p = 0.03). The highest and lowest seropositivity rates were observed in children aged 1-5 (6 samples, 75%) and 5-15 (2 samples, 25%) years old, respectively (p = 0.02). Anti-Toxocara antibodies were positive in 249 samples, (16.1%, 95% CI: 13.2-18.8), which were primarily males. There was a significant difference in seropositivity to Toxocara infection by city (p = 0.04), and age (p = 0.00). The results of Wright test showed seropositivity of 7.5% (117 samples) with the highest rate in individuals aged ≥ 10 years, males, and urban areas. No significant differences existed between the seropositivity rate and age, sex, residency, or symptoms (p > 0.05). Widal test was positive in 6% (94 samples) of children, with most cases being females (p < 0.05), particularly in those aged ≥ 10 years. Of the 78 DAT-positive sera, only 2 samples with a low titer (1:800) tested positive for anti-Toxocara antibodies, while none of the high titer samples were positive. In addition, samples with a DAT titer of 1:800 were positive for anti-Brucella (1:40: 10.2%, 1:80: 2.5%) and Salmonella (1:40: 3.8%) antibodies. The titers were (1:40: 5.1%, 1:80: 1.3%) for Brucella and (1:40: 2.5%) for Salmonella at a 1:1600 DAT titer. Wright's test on Toxocara-positive sera showed that 1.2% and 0.4% of samples had titers of 1:40 and 1:80, respectively. Furthermore, 2%, 2.8%, and 0.8% of Toxocara-positive samples exhibited anti-Salmonella antibodies at titers of 1:40, 1:40, and 1:80 corresponding to OA and OD antigens, respectively. The Wright (OR:1.099; 95% CI:1.080-1.118) and Widal (OR: 1.078; 95% CI: 1.062-1.094) tests showed cross-reactivity at low titers and minimal co-infection at high titers. Of Widal-positive sera, 11.4% with a titer of 1:40, and 2.7% with a titer of 1:80 were positive for anti-Brucella antibodies (OR:1.078; 95% CI:1.056-1.085).

CONCLUSION

Given the prevalence of bacterial and parasitic febrile infections among children in the region, and their symptomatic similarity to VL, it is crucial to recognize clinical manifestations, accurately diagnose co-infections, and account for cross-reactivity in serological tests.

Diagnostic Performance of Three rK39 Rapid Diagnostic Tests and Two Direct Agglutination Tests for the Diagnosis of Visceral Leishmaniasis in Southern Iran

To evaluate the diagnostic performance of five alternative serodiagnostic tests, serum samples from 100 confirmed visceral leishmaniasis (VL) patients, 197 healthy endemic individuals, and 58 non-VL patients living in southern Iran were compared. The VL patients were defined as individuals with a positive result of the immunofluorescent antibody test (IFAT), having clinical signs and symptoms and appropriate response to treatment. The index tests were two direct agglutination tests, DAT-ITM (Institute of Tropical Medicine, Antwerp, Belgium) and DAT-KIT (Royal Tropical Institute, Amsterdam, The Netherlands), and three rapid diagnostic tests (RDTs), Kalazar Detect (InBios International Inc., USA), IT Leish (Bio-Rad, catalog 710124), and Leishmania test (Cypress Diagnostic Company, Belgium). Sensitivities of DAT-ITM and DAT-KIT were low, respectively, 56% and 59%, while specificities were acceptable, respectively, 98% and 93%. Observed sensitivities and specificities of RDTs were higher (71%, 81%, 70% and 99%, 99%, 98% for Kalazar Detect, IT Leish, and Leishmania test, respectively). Even with a maximum sensitivity of 81%, RDTs missed almost one-fifth of VL patients that were positive in IFAT. We conclude that RDTs in VL patients do not possess adequate performance in southern Iran and require some improvement, but they can still be helpful in the diagnosis and screening of the disease in this region due to their high specificity and speed.

Mediterranean visceral leishmaniasis : update on biological diagnosis

Visceral leishmaniasis (VL) is a severe life threatening parasitosis requiring early management of cases. It is an emerging disease in the Mediterranean region with a spread of endemic areas and an increase in case incidence. The patient profile has also evolved with more affected adults, presenting generally non-specific symptoms. Hence the interest of a systematic biological confirmation. The microscopic detection of Leishmania amastigotes in bone marrow aspirates (BMA) smears is the gold standard diagnostic technique. However, it requires invasive sampling. Serological tests searching for specific antibodies remain highly contributory, but their interpretation must always take into account the epidemiological context and the patient's clinical and biological features. Currently, the Western-Blot represents the most specific serological technique for diagnostic confirmation. VL diagnosis has greatly improved by the introduction of both rapid diagnostic tests (RDTs) and molecular biological techniques. RDTs using recombinant rk39 antigen are easy to perform and deliver results in less than 30 minutes. Real-time PCR (Polymerase Chain Reaction) is currently retained as the best technique for VL diagnosis. It is efficient on simple blood samples, allowing to avoid invasive BMA needed for microscopy. In addition, real time PCR estimates parasite load which is helpful for the post-treatment follow-up. In any case, the choice of techniques to be used should be strategic and adapted to the local epidemiology as well as to the means available.

A comparative study of nested-PCR and direct agglutination test (DAT) for the detection of Leishmania infantum infection in symptomatic and asymptomatic domestic dogs

Objective

Canine visceral leishmaniasis (CVL) is the main source of human visceral leishmaniosis (HVL) in Mediterranean region, including Iran and is spread from domestic dogs to Phlebotomine sand flies vectors to humans. To control the transmission of HVL, early and accurate detection of infected dogs is paramount importance despite it remains a confronting challenge. Herein, we evaluated the performance of direct agglutination test (DAT) against gold standard nested polymerase chain reaction (nested-PCR) for CVL diagnosis in symptomatic and asymptomatic domestic dogs from endemic areas of Iran.

Results

Venous blood samples were collected from dogs without clinical signs (n  =  30) and with clinical signs (n  =  35) suggestive of Leishmania infantum infection. Among 65 samples examined, Leishmania DNA was detected by nested-PCR in 89.23% (58/65). Furthermore, 86.15% (56/65) nested-PCR positive samples were also DAT positive. The results of the DAT sensitivity test were 96.43% and 96.67% in symptomatic and asymptomatic dogs, respectively, while the specificity was 100.00% and 60.00% in symptomatic and asymptomatic dogs, respectively. The results of this study also pointed out substantial concordance between DAT test and nested-PCR method in both symptomatic dogs (Κ  =  0.783; P  <  0.001) and asymptomatic dogs (Κ  =  0.618; P  <  0.001). Thus, DAT represents as a simple and economic tool for initial diagnosis of CVL particularly in endemic areas of the disease.

The Emergence of Co-Infection of Visceral Leishmaniasis in an Iranian Child with Chronic Granulomatous Disease: A Case Report

Chronic granulomatous disease (CGD) described as an essential immunodeficiency problem of phagocytic cells resulting in a phagocyte dysfunction and inability to kill a spectrum of bacteria and fungi. Despite the fact that CGD patients are more susceptible to intracellular infections, visceral leishmaniasis has been reported rarely in these cases. Here, we report an uncommon case of visceral leishmaniasis in a child with CGD. An 8-yr old boy with CGD presented to the infectious disease ward, Children’s Medical Center, Tehran University of Medical Sciences, Iran after the onset of 20 days fever with chronic crusted ulcer approximately 3 cm × 3cm on the left upper limb and a small ulcer measuring 0.5 cm × 0.5 cm on the right knee with moderate secretion. Bone Marrow Aspiration (BMA) and Bone Marrow Biopsies (BMB) of fragmented samples were performed and polymorphic population of hematopoietic cells, Megakaryocytes and Leishman bodies were seen. The patient was treated with meglumine antimoniate (Glucantime^®) 20 mg/kg for 28 days and after partial improvement patient discharged and continue the treatment at home. Amphotericin B lipid complex (Ambisome^®) (3–5 mg/kg per dose once) was administered every 3–4 weeks for 18 months as secondary prophylaxis that was well tolerated and effective.

The diagnostic accuracy of direct agglutination test for serodiagnosis of human visceral leishmaniasis: a systematic review with meta-analysis

BACKGROUND

Direct agglutination test (DAT) as a simple, accurate and reliable method, has been widely used for serodiagnosis of visceral leishmaniasis (VL) during the last three decades. The present study is a systematic review and meta-analysis to evaluate the diagnostic accuracy of DAT for serodiagnosis of human VL.

METHODS

Electronic databases, including MEDLINE (via PubMed), SCOPUS, Web of Science, SID and Mag Iran (two Persian scientific search engines) were searched from December 2004 to April 2019. We determined the pooled sensitivity and specificity rates of DAT for the diagnosis of human VL, calculated positive and negative likelihood ratios (LR+ and LR-), and constructed summary receiver operating characteristic (ROC) curves parameters across the eligible studies.

RESULTS

Of the 2928 records identified in the mentioned electronic databases and after examining reference lists of articles, 24 articles met inclusion criteria and were enrolled in the systematic review and out of them 20 records qualified for meta-analysis. The pooled sensitivity and specificity rates of DAT was 96% [95% CI, 92-98] and 95% [CI95% 86-99], respectively. The likelihood ratio of a positive test (LR+) was found to be 21 [CI95%, 6.6-66.5] and the likelihood ratio of a negative test (LR-) was found to be 0.04 [(CI95%, 0.02-0.08]. The combined estimate of the diagnostic odds ratio for DAT was high [467 (CI95%, 114-1912]). We found that the summary receiver operating characteristic curve (SROC) is positioned near the upper left corner of the curve and the area under curve (AUC) was 0.98 (95% CI, 0.97 to 0.99).

CONCLUSION

Referring to our analysis, we determined that DAT can be considered as a valuable tool for the serodiagnosis of human VL with high sensitivity and specificity. As DAT is a simple, accurate and efficient serological test, it can be recommended for serodiagnosis of human VL particularly in endemic areas.

A spotlight on the diagnostic methods of a fatal disease Visceral Leishmaniasis

Leishmania donovani (a causative agent of visceral leishmaniasis) poses a serious health threat to the human population which is fatal if left untreated. The life cycle of Leishmania alternates between vertebrate host and Phlebotomine fly as intermediate ones. Due to the difficulties linked to vector (sandfly) control and the lack of an effective vaccine, the control of leishmaniasis relies mostly on chemotherapy. Unfortunately, the prevalence of parasites becoming resistant to the first-line drug pentavalent antimonial (Sb^V )/sodium antimony gluconate (SAG) and some other anti-leishmanial drug is increasing in several parts of the world. With the alarming rise of drug resistance and other issues related to VL, there is an urgent need to focus on early detection and quick diagnosis of VL case. Therefore, we have reviewed most of the methods used in the diagnostic process of VL. Along with existing diagnostic methods, developing more effective and sensitive diagnostic methods and biomarkers is also vital for enhancing VL identification and control programs. This review gathers the comprehensive information on diagnostics methods of VL under a single umbrella that could be the prominent tools for the development of rapid, accurate and cost-effective diagnostic kits for VL which can be used in field conditions.

Comparison of recombinant A2-ELISA with rKE16 dipstick and direct agglutination tests for diagnosis of visceral leishmaniasis in dogs in Northwestern Iran

INTRODUCTION

Various methods are used for the diagnosis of visceral leishmaniasis (VL), such as microscopic examination, culture and inoculation of laboratory animals; however, serological assays are commonly used for the detection of antibodies in serum samples with a wide range of specificity and sensitivity.

METHODS

The purpose of this study was to compare three serological methods, including rA2-ELISA, the recombinant KE16 (rKE16) dipstick test and the direct agglutination test (DAT), for the detection of antibodies against VL antigens. The assays utilized 350 statistically based random serum samples from domestic dogs with clinical symptoms as well as samples from asymptomatic and healthy dogs from rural and urban areas of the Meshkinshahr district, northwestern Iran.

RESULTS

Samples were assessed, and the following positive rates were obtained: 11.5% by rKE16, 26.9% by DAT and 49.8% by ELISA. The sensitivity among symptomatic dogs was 32.4% with rKE16, 100% with DAT and 52.9% with ELISA. Conversely, rA2-ELISA was less specific for asymptomatic dogs, at 46.5%, compared with DAT, at 88.9%.

CONCLUSIONS

This study recommends rA2-ELISA as a parallel assay combined with DAT to detect VL infection among dogs. Further evaluations should be performed to develop an inexpensive and reliable serologic test for the detection of Leishmania infantum among infected dogs.

Rapid tests for the diagnosis of visceral leishmaniasis in patients with suspected disease

BACKGROUND

The diagnosis of visceral leishmaniasis (VL) in patients with fever and a large spleen relies on showing Leishmania parasites in tissue samples and on serological tests. Parasitological techniques are invasive, require sophisticated laboratories, consume time, or lack accuracy. Recently, rapid diagnostic tests that are easy to perform have become available.

OBJECTIVES

To determine the diagnostic accuracy of rapid tests for diagnosing VL in patients with suspected disease presenting at health services in endemic areas.

SEARCH METHODS

We searched MEDLINE, EMBASE, LILACS, CIDG SR, CENTRAL, SCI-expanded, Medion, Arif, CCT, and the WHO trials register on 3 December 2013, without applying language or date limits.

SELECTION CRITERIA

This review includes original, phase III, diagnostic accuracy studies of rapid tests in patients clinically suspected to have VL. As reference standards, we accepted: (1) direct smear or culture of spleen aspirate; (2) composite reference standard based on one or more of the following: parasitology, serology, or response to treatment; and (3) latent class analysis.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed quality of included studies using the QUADAS-2 tool. Discrepancies were resolved by a third author. We carried out a meta-analysis to estimate sensitivity and specificity of rapid tests, using a bivariate normal model with a complementary log-log link function. We analysed each index test separately. As possible sources of heterogeneity, we explored: geographical area, commercial brand of index test, type of reference standard, disease prevalence, study size, and risk of bias (QUADAS-2). We also undertook a sensitivity analysis to assess the influence of imperfect reference standards.

MAIN RESULTS

Twenty-four studies containing information about five index tests (rK39 immunochromatographic test (ICT), KAtex latex agglutination test in urine, FAST agglutination test, rK26 ICT, and rKE16 ICT) recruiting 4271 participants (2605 with VL) were included. We carried out a meta-analysis for the rK39 ICT (including 18 studies; 3622 participants) and the latex agglutination test (six studies; 1374 participants). The results showed considerable heterogeneity. For the rK39 ICT, the overall sensitivity was 91.9% (95% confidence interval (95% CI) 84.8 to 96.5) and the specificity 92.4% (95% CI 85.6 to 96.8). The sensitivity was lower in East Africa (85.3%; 95% CI 74.5 to 93.2) than in the Indian subcontinent (97.0%; 95% CI 90.0 to 99.5). For the latex agglutination test, overall sensitivity was 63.6% (95% CI 40.9 to 85.6) and specificity 92.9% (95% CI 76.7 to 99.2).

AUTHORS' CONCLUSIONS

The rK39 ICT shows high sensitivity and specificity for the diagnosis of visceral leishmaniasis in patients with febrile splenomegaly and no previous history of the disease, but the sensitivity is notably lower in east Africa than in the Indian subcontinent. Other rapid tests lack accuracy, validation, or both.

Developments in diagnosis and treatment of visceral leishmaniasis during the last decade and future prospects

Human visceral leishmaniasis (VL) continues to be a life-threatening neglected tropical disease, with close to 200 million people at risk of infection globally. Epidemics and resurgence of VL are associated with negligence by the policy makers, economic decline and population movements. Control of the disease is hampered by the lack of proficient vaccination, rapid diagnosis in a field setting and severe side effects of current drug therapies. The diagnosis of VL relied largely on invasive techniques of detecting parasites in splenic and bone marrow aspirates. rK39 and PCR, despite problems related to varying sensitivities and specificities and field adaptability, respectively, are considered the best options for VL diagnosis today. No single therapy of VL currently offers satisfactory efficacy along with safety. The field of VL research only recently shifted toward actively identifying new drugs for safe and affordable treatment. Oral miltefosine and safe AmBisome along with better use of amphotericin B have been rapidly implemented in the last decade. A combination therapy will substantially reduce the required dose and duration of drug administration and reduce the chance of the development of resistance. In addition, identification of asymptomatic cases, vector control and treatment of post-kala-azar dermal leishmaniasis would allow new perspectives in VL control and management.

Canine visceral leishmaniasis: a comparative study of real-time PCR, conventional PCR, and direct agglutination on sera for the detection of Leishmania infantum infection

Canine visceral leishmaniasis (CVL) is endemic in northwestern Iran. This study aimed to compare real-time PCR, conventional PCR, and the direct agglutination test (DAT) for the diagnosis Leishmania infantum infection in 167 serum samples of domestic dog. Bone marrow was used for parasitological examination (smears and/or culture) in symptomatic visceral leishmaniasis, and serum was used for detection of L. infantum kinetoplast DNA (kDNA) by both conventional PCR and real-time PCR, while anti-L. infantum antibodies in sera were measured by DAT. The sera were collected from 37 symptomatic and 112 asymptomatic dogs during April to May 2011. Eighteen presumed negative samples were obtained from healthy dogs kept in non-endemic areas with no history of CVL and used as controls. All 18 samples were negative by DAT and Dipstick rK39. DAT confirmed previous exposure to L. infantum for all 149 serum samples collected from symptomatic and asymptomatic dogs in CVL endemic areas of Iran. Among the 37 symptomatic dogs, 20 (54%), 25 (67.6%), 36 (97.3%), and 37 (100%) showed L. infantum infection by parasitological methods, conventional PCR, real-time PCR, and DAT (≥ 1:80), respectively. Of 112 asymptomatic dogs, 79 (70.5%), 111 (99.1%), and 112 (100%) were shown to be positive by conventional PCR, and DAT (≥ 1:80), respectively. For ethical reasons, no asymptomatic or healthy control dogs were examined by parasitological methods. Three (16.7%) control dogs were positive by real-time PCR, but were negative by DAT, dipstick rK39, and conventional PCR methods. Parasitemia levels were measured by real-time PCR targeting kDNA using SYBR(®) green assay. This quantitative technique detected infection in 89.9% (150/167) of the domestic dogs that harbored L. infantum kDNA, ranging from 0.01 49 to 310.1 parasites/ml. The average was 16.60 parasites/ml. A good agreement (0.97) was found between real-time PCR and DAT at ≥ 1:80 titer, used as cut-off value by Kappa analysis. Thus, real-time PCR as a quantitative PCR assay on serum samples represents a valuable tool for initial diagnosis of CVL when whole blood is not available.