Standardization of a rapid immunochromatographic test with the recombinant antigens K39 and K26 for the diagnosis of canine visceral leishmaniasis

Rapid and reliable detection of Leishmania antibodies in canine serum with double-antigen sandwich homogeneous chemical luminescence

BACKGROUND

Leishmaniasis, caused by Leishmania spp. parasites, is an important zoonotic disease globally, posing severe threats to humans and animals. In the absence of effective vaccines, reliable serological diagnostic methods are critical for disease control. However, the enzyme-linked immunosorbent assay (ELISA) and immunochromatographic assay have limitations due to complexity, time required and/or sensitivity. Therefore, our objective was to develop an accurate, rapid and user-friendly detection method of canine leishmania antibody based on double-antigen sandwich homogeneous chemical luminescence.

METHODS

Homogeneous chemiluminescent technology was employed, and expressed recombinant fusion proteins containing full-length K9, K39 and K26 repeat sequences were used as diagnostic antigens. To establish a dual-antigen sandwich serological assay capable of detecting various antibody types, a factorial design was used to optimize concentrations of diagnostic antigen-receptor microspheres and of biotinylated diagnostic antigens, as well as of reaction solution composition and reaction duration. To evaluate and validate this newly developed method, we collected 41 Leishmania-positive serum samples, 30 Leishmania-negative control serum samples and 78 clinical serum samples for which no diagnostic information was available. Comparative analyses were performed using parasitological testing and an indirect ELISA as reference methods, focusing on diagnostic sensitivity and specificity.

RESULTS

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis confirmed the purification of the diagnostic antigens, which exhibited clear bands without impurities. Based on results from the 41 Leishmania-positive samples and 30 Leishmania-negative samples, there was sufficient sensitivity to detect samples diluted up to 256-fold, with analytical specificity of 100%. Overall diagnostic sensitivity was 100% and diagnostic specificity was 93.3%. Diagnostic performance was highly consistent between the newly developed method and the indirect ELISA (Kappa = 0.82, P < 0.01). Testing could be completed within 35 min with the new method CONCLUSIONS: We have developed a novel double-antigen sandwich homogeneous chemical luminescence method to detect canine Leishmania antibodies, with high sensitively and specificity, a short incubation interval and a simple protocol. This streamlined approach not only offers a sensitive and efficient method for clinical diagnosis but also has great potential for use in automated testing.

Comparative Study of a Novel Lateral Flow Rapid Test with Conventional Serological Test Systems for the Diagnosis of Canine Leishmaniosis in Croatia and Brazil

Control of canine infections with Leishmania infantum (L. infantum), a major zoonotic disease in Brazil and southern Europe, is becoming increasingly important due to its close proximity to humans, the increasing import of dogs from endemic regions and the impact of climate change on vector spreading. Simple, rapid and reliable diagnostic tests are therefore needed to detect infected dogs. Here, we re-evaluated different serological methods for the diagnosis of canine leishmaniosis (CanL) in Croatia and Brazil. The diagnostic performance of the indirect fluorescent antibody test (IFAT) and the VetLine® Leishmania ELISA (GSD Frankfurt, Germany) was compared with three rKLi8.3-based diagnostic test systems, the rKLi8.3 ELISA (GSD Frankfurt, Germany), the INgezim® Leishma CROM (GSD Madrid, Spain) lateral flow test (LFT) and the VetBlot®Leishmania LineBlot (GSD Frankfurt, Germany). CanL symptomatic dogs were efficiently diagnosed by all tests, except the VetLine® Leishmania ELISA, which is based on whole Leishmania antigens. The advantage of rKLi8.3 was also observed in oligo- and asymptomatic dogs from Brazil and Croatia, although with reduced diagnostic efficiency compared to symptomatic dogs. Similar to IFAT and rKLi8.3 ELISA, the LFT did not cross-react with other common canine pathogens; it showed very high specificity for healthy dogs from endemic regions in both countries and did not react with healthy, vaccinated dogs in Brazil. In conclusion, serodiagnostic tests based on the rKLi8.3 antigens are superior to whole parasite antigens, and the LFT has the advantage of providing a laboratory-independent, rapid and specific diagnosis of CanL.

Serodiagnosis of leishmaniasis in asymptomatic and symptomatic dogs by use of the recombinant dynamin-1-like protein from Leishmania infantum: A preliminary study

Visceral leishmaniasis (VL) is a fatal manifestation of an infection caused by intracellular protozoa of the Leishmania genus. In New World countries, VL is classified as a zoonotic disease with domestic dogs acting as its main reservoir. Asymptomatic dogs are as competent to transmit Leishmania to the vectors as symptomatic dogs, however current diagnostic tests are limited and present low sensitivity for this important group. The development of accurate tests is fundamental to the early diagnosis, treatment, and control of canine leishmaniasis. In this study, we investigated the use of a recombinant protein (dynamin-1-like protein, Dyn-1) from L. infantum, as a potential target antigen for leishmaniasis serodiagnosis in both symptomatic and asymptomatic dogs. The antigenic performance of the protein was evaluated by means of ELISA assays using sera from symptomatic (n = 25), asymptomatic (n = 34) and non-infected dogs (n = 36) using ELISA. In addition, sera from dogs experimentally infected with Trypanosoma cruzi (n = 49) and naturally infected with Babesia sp. (n = 8) were tested to evaluate possible cross-reactivity. A crude soluble antigen (CSA) of Leishmania was used as an antigen control and K39 and K26 were used as reference antigens because they are already widely used in commercial tests. rDyn-1-based assay showed the highest sensitivity (97%) compared to the antigens K39 (88%), K26 (86%) and crude extract (95%). The highest specificity among the tests was also obtained with the protein rDyn-1 (94%), compared with the other antigens K39 (81%), K26 (87%), and crude extract (77%). This study showed that the rDyn-1 ELISA assay was able to identify 100% of asymptomatic dogs, establishing its potential as a target for the diagnosis of canine leishmaniasis.

Validation of an immunochromatographic assay kit based on colored latex particles for the identification of the canine visceral leishmaniasis

Visceral leishmaniasis is a zoonotic infectious disease with a severe impact on humans and animals. Infection is transmitted by phlebotomine sand flies. The dogs are main reservoir for human infection. A rapid and accurate diagnosis of canine visceral leishmaniasis is essential for an efficient surveillance program. The aim of this study was to assess the performance of a rapid immunochromatographic strip test based on functionalized colored particles and a new recombinant antigenic protein, as a visual "in situ" method for the diagnosis of canine visceral leishmaniasis. The results were evaluated using an in-house ELISA assay with the same antigen. Both tests produced concordant results and the immunochromatographic strip test showed good diagnostic sensitivity (98%) and specificity (95%). Finally, meta-analysis was used to compare the sensitivity and specificity of the here developed test with the results of commercial immunochromatographic strip tests obtained from literature.

Chagas Immunochromatographic Rapid Test in the Serological Diagnosis of Trypanosoma cruzi Infection in Wild and Domestic Canids

Canis lupus familiaris (domestic dog) represents a reliable sentinel for the occurrence of a well-established transmission cycle of Trypanosoma cruzi among wild mammals in the surroundings and, consequently, where the risk of human infection exists. Serological diagnosis is the chosen method to identify T. cruzi infection in dogs that, in Brazil, rarely present positive parasitological tests. The use of recombinant chimeric parasitic antigens results in a sensitive and specific serological diagnostic test in contrast to the use of crude T. cruzi antigens. Our objective was to evaluate the Chagas/Bio-Manguinhos Lateral Flow Immunochromatographic Rapid Test (Chagas-LFRT) for the diagnosis of T. cruzi infection in domestic dogs and the potential of application of this diagnostic platform to wild canid species. Two recombinant proteins (IBMP-8.1 and IBMP-8.4) that displayed the best performance in the enzyme immunoassay (ELISA) in previous studies were tested in a platform with two diagnostic bands. A panel of 281 dog serum samples was evaluated: 133 positive for T. cruzi by serological diagnosis, including 20 samples with positive blood cultures belonging to different discrete typing units (DTUs); 129 negative samples; and 19 samples from dogs infected by other trypanosomatids: Leishmania infantum, Trypanosoma rangeli, Trypanosoma caninum and Crithidia mellificae, in addition to samples infected by Anaplasma platys, Dirofilaria immitis and Erlichia sp. that were employed to evaluate eventual cross-reactions. We also evaluated the Chagas-LFRT to detect T. cruzi infection in 9 serum samples from six wild canid species. We observed that the intensity pattern of the bands was directly proportional to the serological titer observed in IFAT. The sensitivity was 94%, the specificity was 91% according to the ROC curve, and the defined cutoff was an optical density of 4.8. The agreement obtained was considered substantial by the kappa analysis (84%). From T. cruzi positive hemoculture samples, 88.9% were positive by Chagas-LFRT. The test was efficient in recognizing infections by five of the six T. cruzi DTUs. Cross-reactions were not observed in infections by L. infantum, T. rangeli, T. caninum and D. immitis; however, they were observed in sera of dogs infected by Crithidia mellificae, Anaplasma sp. and Erlichia sp. A strong reaction was observed when serum samples from wild canids were submitted to the Protein A affinity test, confirming its applicability for these species. This test will allow rapid preventive actions in areas with high risk to the emergence of Chagas disease in a safer, reliable, low-cost and immediate manner, without the need for more complex laboratory tests.

Leishmania infantum infecting the carnivore Nasua nasua from urban forest fragments in an endemic area of visceral leishmaniasis in Brazilian Midwest

Introduction

The aim of the present study was to investigate the occurrence of Leishmania infantum in South American coatis inhabiting two forest fragments in Campo Grande, Mato Grosso do Sul, Midwest region of Brazil, an endemic area of human and canine visceral leishmaniasis (VL).

Material and methods

A total of 110 South American coatis were sampled in the conservation unit "Parque Estadual do Prosa" (PEP) and in the residential area "Vila da Base Aérea" (VBA) from March 2018 to April 2019. As a longitudinal study that include up to six recaptures of the same individual, a total of 190 capture events were obtained. Blood, bone marrow and skin samples were obtained for parasitological (axenic culture), serological (Enzyme Linked Immunosorbent Assay - ELISA and Dual-path Platform immunoassay - DPP^® CVL) and molecular diagnostic assays (targeting kDNA for Leishmania spp. and L. infantum; and HSP70 followed by sequence analysis).

Results

Seropositivity for L. infantum was found in 33 individuals, six in PEP and 27 in VBA. Furthermore, L. infantum was detected by molecular analysis in 16 individuals, seven from PEP and nine from VBA. We also isolated L. infantum from bone marrow of one individual and detected a single positive skin sample in molecular assay from other individual, both from VBA.

Discussion

An overall infection rate of 36.4% (40/110) was observed, significantly higher in the VBA (49.1%) than in the PEP (21.6%), probably because VBA presents: (i) a large number of resident dogs and chickens that would be attracting sandflies; (ii) a denser population of this wild mammal species; and (iii) physical barriers and a lack of functional connectivity in the surroundings, preventing these animals to disperse out. We conclude that South American coati populations living in urban forest fragments of Campo Grande are affected by the epidemiological scenario of VL, known to involve dogs, vectors and humans. We highlight the importance of investigate the parasitism by L. infantum in this and other potential L. infantum reservoirs that inhabit urbanized regions endemic to VL.

Epidemiology of Vector-Borne Pathogens Among U.S. Government Working Dogs

Surveillance of U.S. domestic dogs for exposure to vector-borne pathogens can identify regions of transmission that are relevant for human and animal health. Working dogs with high levels of outdoor exposure may be sensitive indicators of local risk, owing to increased contact with vectors. We randomly selected 476 high-value government working dogs from 40 states to determine the prevalence of infection with Dirofilaria immitis and Rickettsia spp., and exposure to Ehrlichia spp., Anaplasma spp., and Borrelia burgdorferi, and identify risk factors for positivity. Additionally, we tested 100 of these dogs from Texas for Leishmania spp. where sand fly vectors occur. Previously published Trypanosoma cruzi infection data on these dogs were used to identify coinfection or co-exposures. Infection prevalence was 0.84% for D. immitis, and all dogs were negative for Rickettsia spp. DNA. Seroprevalence of each pathogen was: B. burgdorferi 0.84%, Ehrlichia spp. 1.3%, Anaplasma spp. 1.5%, Leishmania spp. 2.0%, and T. cruzi 12.2%. Coinfection or co-exposure took place in four (0.84%) dogs. In bivariable analysis, we found that D. immitis-positive and Ehrlichia-seropositive dogs were significantly older than negative dogs (p < 0.05). Furthermore, seroprevalence of Anaplasma spp. was significantly higher among dogs in the Northeast United States relative to other areas of the country (4.7% vs. ≤1.4%; p = 0.041). Although autochthonous Leishmania infections have been described in the United States, the cases reported herein may represent imported Leishmania infection. Most federal working dogs are bred in Europe, where the parasite is endemic and congenitally transmitted. Serological cross-reaction between T. cruzi and Leishmania spp. complicates diagnosis. In this study, the use of multiple testing strategies in a comparative complementary manner provided evidence for these dogs' true exposures. Comprehensive surveillance for vector-borne pathogens in dogs can improve clinician awareness and target prevention and treatment in a One Health manner.

Canine visceral leishmaniasis in area with recent Leishmania transmission: prevalence, diagnosis, and molecular identification of the infecting species

INTRODUCTION:

Canine visceral leishmaniasis (CVL) is an endemic disease in Brazil, and integrated control actions have been adopted by the Brazilian Ministry of Health to control its spread. However, the transmission profile is unknown in areas with recent CVL cases, including Itaúna, located in the Brazilian state of Minas Gerais, where the present study was carried out.

METHODS:

A total of 2,302 dogs from 12 neighborhoods were serologically tested for canine VL using the current diagnostic protocol adopted by the Brazilian Ministry of Health. Test positivity rate (TPR) and CVL prevalence were determined for each neighborhood. The presence of Leishmania was assessed in 60 seropositive dogs which had been recommended for euthanasia. Twenty-two of them (37%) were asymptomatic, and 38 (63%) were symptomatic for CVL. Parasitological (myeloculture and smear/imprint) and molecular (PCR) methods were employed for Leishmania detection in bone marrow, spleen, mesenteric lymph nodes, and ear skin. The infecting Leishmania species was identified by DNA sequencing.

RESULTS:

CVL prevalence (per 1,000 dogs) varied from 0.0-166.67, depending on the neighborhood, with a mean of 68.96 (SD 51.38). Leishmania DNA was detected in at least one tissue from all seropositive dogs, with comparable TPR among tissues. Leishmania parasites were identified in most (54/60) seropositive dogs, and the infecting parasite was identified as Leishmania infantum in all of these.

CONCLUSIONS:

Prevalence of CVL is a contributor to the spread of visceral leishmaniasis in Itaúna.

Canine visceral leishmaniasis biomarkers and their employment in vaccines

The natural history of canine visceral leishmaniasis (CVL) has been well described, particularly with respect to the parasite load in different tissues and immunopathological changes according to the progression of clinical forms. The biomarkers evaluated in these studies provide support for the improvement of the tools used in developing vaccines against CVL. Thus, we describe the major studies using the dog model that supplies the rationale for including different biomarkers (tissue parasitism, histopathology, hematological changes, leucocytes immunophenotyping, cytokines patterns, and in vitroco-culture systems using purified T-cells subsets and macrophages infected with L. infantum) for immunogenicity and protection evaluations in phases I and II applied to pre-clinical and clinical vaccine trials against CVL. The search for biomarkers related to resistance or susceptibility has revealed a mixed cytokine profile with a prominent proinflammatory immune response as relevant for Leishmania replication at low levels as observed in asymptomatic dogs (highlighted by high levels of IFN-γ and TNF-α and decreased levels in IL-4, TGF-β and IL-10). Furthermore, increased levels in CD4⁺ and CD8⁺ T-cell subsets, presenting intracytoplasmic proinflammatory cytokine balance, have been associated with a resistance profile against CVL. In contrast, a polyclonal B-cell expansion towards plasma cell differentiation contributes to high antibody production, which is the hallmark of symptomatic dogs associated with high susceptibility in CVL. Finally, the different studies used to analyze biomarkers have been incorporated into vaccine immunogenicity and protection evaluations. Those biomarkers identified as resistance or susceptibility markers in CVL have been used to evaluate the vaccine performance against L. infantum in a kennel trial conducted before the field trial in an area known to be endemic for visceral leishmaniasis. This rationale has been a guiding force in the testing and selection of the best vaccine candidates against CVL and provides a way for the veterinary industry to register commercial immunobiological products.

Validation of the Dual-path Platform chromatographic immunoassay (DPP® CVL rapid test) for the serodiagnosis of canine visceral leishmaniasis

BACKGROUND Visceral leishmaniasis is a major public health challenge in South America, and dogs are its main urban reservoir. OBJECTIVE Validation of the canine Dual-path Platform immunoassay for canine visceral leishmaniasis (DPP® CVL) for a sample set composed of 1446 dogs from different Brazilian endemic areas. METHODS A well-defined reference standard by means of parasitological culture, immunohistochemistry, and histopathology was used. Animals were classified as asymptomatic, oligosymptomatic, or symptomatic. Sensitivity and specificity were assessed as a single set and in clinical groups. A reproducibility assessment of the tests was conducted using the Kappa (κ) index at three different laboratories (A, B, and C). FINDINGS Overall, 89% sensitivity and 70% specificity were obtained for the entire sample set. Analysis of the clinical groups showed a gradual decrease in the sensitivity and an increase in the specificity with the reduction of clinical signs in the dogs that were assessed, reaching a sensitivity of 75% (42.8-94.5%) among asymptomatic dogs and lower specificity of 56% (46.2-66.3%) among symptomatic dogs. Inter-laboratory agreement was substantial (κAB= 0.778; κAC= 0.645; κCB= 0.711). MAIN CONCLUSIONS The test performance is somewhat dependent on canine symptomatology, but such influence was less evident than in previous studies. Favourable results for sensitivity and specificity can be obtained even in asymptomatic animals; however, caution is needed in these evaluations, and the results suggest that the immunochromatographic test may be further improved for better investigation in asymptomatic dogs. The results obtained confirm the usefulness of DPP® CVL for application in serological surveys.

Canine visceral leishmaniasis: Diagnosis and management of the reservoir living among us

This article reviews essential topics of canine visceral leishmaniasis (CVL) due to Leishmania infantum infection. It focuses on the current serological and molecular diagnostic methods used in epidemiological research and veterinary clinics to diagnose CVL and includes new point-of-care (POC) tests under development. The efficacy of different treatment regimens on the clinical improvement and infectiousness of dogs is also addressed. In the last section, the review provides a critical appraisal of the effectiveness of different control measures that have been implemented to curb disease transmission.

Dogs are the principal reservoir hosts of L. infantum and consequently play a critical role in the transmission cycle of urban VL, which also affects humans. This review provides updated information on important topics such as diagnostic tests and dog treatments that improve dog health and decrease their transmission efficacy to insect vectors. A critical review of control measures is also provided.

Diagnostic accuracy of rKLO8 versus rK26 ELISAs for screening of canine visceral leishmaniasis

Canine visceral leishmaniasis (CVL) represents an important public health issue. Despite numerous diagnostic tests available, CVL diagnosis still needs to be improved to achieve a more accurate detection rate. Recently, rKLO8, a new antigenic protein of Sudanese Leishmania donovani, was studied for the first time in diagnosis of human visceral leishmaniasis (HVL) and showed good performance. The present study aimed to evaluate serum reactivity to rKL08 and the reference antigen rK26, and to compare both diagnostic proteins with the combined DPP^® CVL rapid test and ELISA (EIE-Bio-Manguinhos) confirmatory test, which are both recommended for the diagnosis of CVL in Brazil. Serum samples of dogs were grouped into: (I) DPP^®/EIE negative (n=100) and (II) DPP^®/EIE positive sera (n=100). Enhanced levels of IgG, mainly IgG2, to both rKLO8 and rK26 were found in group II. Sensitivity was 68% and 77% and specificity was 92% and 91%, for rKLO8 and rK26 antigens, respectively. Moreover, the combination of rKLO8 and rK26 antigens (rKLO8+rK26) exhibited higher sensitivity (85%) and specificity (93%). Thus, our results show that apart from the improved diagnostic power of rKLO8 in HVL, this new antigen is also suitable for the diagnosis of CVL. Further, the combination of rKLO8 and rK26 antigens increases the diagnostic accuracy of CVL.

Immunogenicity in dogs and protection against visceral leishmaniasis induced by a 14kDa Leishmania infantum recombinant polypeptide

In areas were human visceral leishmaniasis (VL) is endemic, the domestic dog is the main parasite reservoir in the infectious cycle of Leishmania infantum. Development of prophylactic strategies to lower the parasite burden in dogs would reduce sand fly transmission thus lowering the incidence of zoonotic VL. Here we demonstrate that vaccination of dogs with a recombinant 14kDa polypeptide of L. infantum nuclear transport factor 2 (Li-ntf2) mixed with adjuvant BpMPLA-SE resulted in the production of specific anti-Li-ntf2 IgG antibodies as well as IFN-γ release by the animals' peripheral blood mononuclear cells stimulated with the antigen. In addition, immunization with this single and small 14kDa poplypeptide resulted in protracted progression of the infection of the animals after challenging with a high dose of virulent L. infantum. Five months after challenge the parasite load was lower in the bone marrow of immunized dogs compared to non-immunized animals. The antibody response to K39, a marker of active VL, at ten months after challenge was strong and significantly higher in the control dogs than in vaccinated animals. At the study termination vaccinated animals showed significantly more liver granulomas and lymphoid hyperplasia than non-vaccinated animals, which are both histological markers of resistance to infection. Together, these results indicate that the 14kDa polypeptide is an attractive protective molecule that can be easily incorporated in a leishmanial polyprotein vaccine candidate to augment/complement the overall protective efficacy of the final product.

Multi-antigen print immunoassay (MAPIA)-based evaluation of novel recombinant Leishmania infantum antigens for the serodiagnosis of canine visceral leishmaniasis

Background

Domestic dogs are the principal reservoir hosts of Leishmania infantum in regions where visceral leishmaniasis (VL) is endemic. Although serologic methods are frequently used for the screening of infected dogs, antibody-based tests require further assessment, due to lack of sensitivity and specificity. In this study, we employed a multi-antigen printing immunoassay (MAPIA) to compare the antibody responses to novel recombinant proteins of L. infantum with the potential for the detection of canine VL.

Findings

MAPIA strips were prepared employing 12 recombinant proteins. Antibody reactivity to these antigens was compared using a panel of sera collected from clinically asymptomatic (n = 16) and symptomatic (n = 41) culture-positive animals. Our findings showed that the canine immune response to antigen differs between dogs and depends on infection status. Using this screening assay, when five out of the 12 antigens were combined, an overall 81% detection rate of L. infantum-infected dogs was achieved.

Conclusions

We conclude that MAPIA is an effective screening tool to rapidly select multiple antigens of diagnostic utility to be used in a more sensitive point of care diagnostic test such as the Dual-Path Platform (DPP) multiplex test for the rapid detection of infected dogs.

Comparative evaluation of the DPP(®) CVL rapid test for canine serodiagnosis in area of visceral leishmaniasis

We investigated the performance of the DPP(®) canine visceral leishmaniasis (CVL) rapid test, a novel immunochromatographic assay launched by BioManguinhos (Brazil), which was recently included in the new Brazilian protocol for screening CVL in serological surveys. The present study compared the DPP(®) with the ELISA and IFA produced by BioManguinhos (Brazil) both with L. major-like antigens and with in-house tests using Leishmania infantum chagasi (in-house ELISA and in-house IFA). We analyzed the sera from clinically symptomatic (n=47) and asymptomatic (n=38) infected dogs from an endemic area of CVL, as well as from healthy (n=18) dogs, in addition to the sera of dogs (n=81) infected with other pathogens. The DPP(®) and the in-house ELISA showed a sensitivity of 90.6% and 94.1%, respectively, and specificity of 95.1% and 97.5%, respectively, and both presented cross-reactivity only with the sera of dogs with babesiosis, 44% for the DPP(®) and 22% for the in-house ELISA. The clinical groups were detected equally by the two assays. The ELISA BioManguinhos, IFA BioManguinhos, and in house-IFA showed a good sensitivity, 90.6%, 96.5% and 89.4%, respectively, but very low specificity, 77.8%, 69.1% and 65.8%, respectively, due to the high cross-reactivity with the sera from the animals harboring other pathogens. The in-house ELISA provided the highest accuracy (95.8%), followed by the DPP(®) (92.7%), ELISA BioManguinhos (84.3%), IFA BioManguinhos (83.1%), and in-house IFA (78.0%). The simultaneous use of the DPP(®) and ELISA BioManguinhos reached a sensitivity of 99.1% and 82.1% when used sequentially. In conclusion, the DPP(®) performed well as serological test for CVL, and detected both asymptomatic and symptomatic dogs in equal proportions. Although its sensitivity is not ideal yet, discarding the IFA and including the DPP(®) improved the accuracy of the new Brazilian CVL diagnostic protocol, particularly of detecting truly infected dogs. Moreover, considering the higher specificity of DPP(®) (95.1% vs 77.8%), positive predictive value (95.1% vs 81.1%) and positive likelihood value (18.3% vs 4.1%) in comparison with the ELISA BioManguinhos, the use of DPP(®) as a confirmatory test instead of a screening test is suggested.

Evaluation of change in canine diagnosis protocol adopted by the visceral leishmaniasis control program in Brazil and a new proposal for diagnosis

The techniques used for diagnosis of canine visceral leishmaniasis (CVL) in Brazil ELISA and IFAT have been extensively questioned because of the accuracy of these tests. A recent change in the diagnosis protocol excluded IFAT and included the Dual-Path Platform (DPP). We evaluated the prevalence and incidence rates of Leishmania spp. before and after the change in the protocol. In addition, based on our results, we propose a new alternative that is less expensive for the screening and confirmation of CVL. Plasma samples were obtained from a serobank from dogs evaluated in a cross-sectional study (1,226 dogs) and in a cohort study of susceptible animals (n = 447), followed for 26 months. Serology testing was performed using ELISA, IFAT, and DPP. The incidence and prevalence of CVL were determined by using the protocol of the Visceral Leishmaniasis Control and Surveillance Program until 2012 (ELISA and IFAT using filter paper) and the protocol used after 2012 (DPP and ELISA using plasma). The prevalence was 6.2% and the incidence was 2.8 per 1,000 dog-months for the protocol used until 2012. For the new diagnosis protocol for CVL resulted in an incidence of 5.4 per 1,000 dog-months and a prevalence of 8.1%. Our results showed that the prevalence and incidence of infection were far greater than suggested by the previously used protocol and that the magnitude of infection in endemic areas has been underestimated. As tests are performed sequentially and euthanasia of dogs is carried out when the serological results are positive in both tests, the sequence does not affect the number of animals to be eliminated by the Control Program. Then we suggest to municipalities with a large demand of exams to use ELISA for screening and DPP for confirmation, since this allows easier performance and reduced cost.

Characterization of the biology and infectivity of Leishmania infantum viscerotropic and dermotropic strains isolated from HIV+ and HIV- patients in the murine model of visceral leishmaniasis

BACKGROUND

Leishmaniasis is a group of diseases with a variety of clinical manifestations. The form of the disease is highly dependent on the infective Leishmania species and the immunological status of the host. The infectivity of the parasite strain also plays an important role in the progression of the infection. The aim of this work is to understand the influence of the natural infectivity of Leishmania strains in the outcome of visceral leishmaniasis.

METHODS

In this study we have characterized four strains of L. infantum in terms of molecular typing, in vitro cultivation and differentiation. Two strains were isolated from HIV+ patients with visceral leishmaniasis (Bibiano and E390M), one strain was isolated from a cutaneous lesion in an immunocompetent patient (HL) and another internal reference strain causative of visceral leishmaniasis (ST) also from an immunocompetent patient was used for comparison. For this objective, we have compared their virulence by in vitro and in vivo infectivity in a murine model of visceral leishmaniasis.

RESULTS

Molecular typing unraveled a new k26 sequence attributed to MON-284 zymodeme and allowed the generation of a molecular signature for the identification of each strain. In vitro cultivation enabled the production of promastigotes with comparable growth curves and metacyclogenesis development. The HL strain was the most infective, showing the highest parasite loads in vitro that were corroborated with the in vivo assays, 6 weeks post-infection in BALB/c mice. The two strains isolated from HIV+ patients, both belonging to two different zymodemes, revealed different kinetics of infection.

CONCLUSION

Differences in in vitro and in vivo infectivity found in the murine model were then attributed to intrinsic characteristics of each strain. This work is supported by other studies that present the parasite's inherent features as factors for the multiplicity of clinical manifestations and severity of leishmaniasis.

Polymorphism in the HASPB repeat region of East African Leishmania donovani strains

BACKGROUND/OBJECTIVES

Visceral leishmaniasis (VL) caused by Leishmania donovani is a major health problem in Ethiopia. Parasites in disparate regions are transmitted by different vectors, and cluster in distinctive genotypes. Recently isolated strains from VL and HIV-VL co-infected patients in north and south Ethiopia were characterized as part of a longitudinal study on VL transmission.

METHODOLOGY/PRINCIPAL FINDINGS

Sixty-three L. donovani strains were examined by polymerase chain reaction (PCR) targeting three regions: internal transcribed spacer 1 (ITS1), cysteine protease B (cpb), and HASPB (k26). ITS1- and cpb--PCR identified these strains as L. donovani. Interestingly, the k26--PCR amplicon size varied depending on the patient's geographic origin. Most strains from northwestern Ethiopia (36/40) produced a 290 bp product with a minority (4/40) giving a 410 bp amplicon. All of the latter strains were isolated from patients with HIV-VL co-infections, while the former group contained both VL and HIV-VL co-infected patients. Almost all the strains (20/23) from southwestern Ethiopia produced a 450 bp amplicon with smaller products (290 or 360 bp) only observed for three strains. Sudanese strains produced amplicons identical (290 bp) to those found in northwestern Ethiopia; while Kenyan strains gave larger PCR products (500 and 650 bp). High-resolution melt (HRM) analysis distinguished the different PCR products. Sequence analysis showed that the k26 repeat region in L. donovani is comprised of polymorphic 13 and 14 amino acid motifs. The 13 amino acid peptide motifs, prevalent in L. donovani, are rare in L. infantum. The number and order of the repeats in L. donovani varies between geographic regions.

CONCLUSIONS/SIGNIFICANCE

HASPB repeat region (k26) shows considerable polymorphism among L. donovani strains from different regions in East Africa. This should be taken into account when designing diagnostic assays and vaccines based on this antigen.

Evaluation of rK39 rapid diagnostic tests for canine visceral leishmaniasis: longitudinal study and meta-analysis

Background

There is a need for sensitive and specific rapid diagnostic tests (RDT) for canine visceral leishmaniasis. The aims of this study were to evaluate the diagnostic performance of immunochromatographic dipstick RDTs using rK39 antigen for canine visceral leishmaniasis by (i) investigating the sensitivity of RDTs to detect infection, disease and infectiousness in a longitudinal cohort study of natural infection in Brazil, and (ii) using meta-analysis to estimate the sensitivity and specificity of RDTs from published studies.

Methodology

We used a rK39 RDT (Kalazar Detect Canine Rapid Test; Inbios) to test sera collected from 54 sentinel dogs exposed to natural infection in an endemic area of Brazil. Dogs were sampled bimonthly for up to 27 months, and rK39 results compared to those of crude antigen ELISA, PCR, clinical status and infectiousness to sandflies. We then searched MEDLINE and Web of Knowledge (1993–2011) for original studies evaluating the performance of rK39 RDTs in dogs. Meta-analysis of sensitivity and specificity was performed using bivariate mixed effects models.

Principal Findings

The sensitivity of the rK39 RDT in Brazil to detect infection, disease and infectiousness was 46%, 77% and 78% respectively. Sensitivity increased with time since infection, antibody titre, parasite load, clinical score and infectiousness. Sixteen studies met the inclusion criteria for meta-analysis. The combined sensitivity of rK39 RDTs was 86.7% (95% CI: 76.9–92.8%) to detect clinical disease and 59.3% (37.9–77.6%) to detect infection. Combined specificity was 98.7% (89.5–99.9%). Both sensitivity and specificity varied considerably between studies.

Conclusion

The diagnostic performance of rK39 RDTs is reasonable for confirmation of infection in suspected clinical cases, but the sensitivity to detect infected dogs is too low for large-scale epidemiological studies and operational control programmes.

Canine visceral leishmaniasis is a vector-borne disease caused by the intracellular parasite Leishmania infantum. It is an important veterinary disease, and dogs are also the main animal reservoir for human infection. The disease is widespread in the Mediterranean area, and parts of Asia and South and Central America, and is potentially fatal in both dogs and humans unless treated. Diagnosis of canine infections requires serological or molecular tests. Detection of infection in dogs is important prior to treatment, and in epidemiological studies and control programmes, and a sensitive and specific rapid diagnostic test would be very useful. Rapid diagnostic tests (RDTs) have been developed, but their diagnostic performance has been reported to be variable. We evaluated the sensitivity of a RDT based on serological detection of the rK39 antigen in a cohort of naturally infected Brazilian dogs. The sensitivity of the test to detect infection was relatively low, but increased with time since infection and the severity of infection. We then carried out a meta-analysis of published studies of rK39 RDTs, evaluating the sensitivity to detect disease and infection. The results suggest that rK39 RDTs may be useful in a veterinary clinical setting, but the sensitivity to detect infection is too low for operational control programmes.

Improved canine and human visceral leishmaniasis immunodiagnosis using combinations of synthetic peptides in enzyme-linked immunosorbent assay

BACKGROUND

Zoonotic visceral leishmaniasis (VL) is a severe infectious disease caused by protozoan parasites of the genus Leishmania and the domestic dogs are the main urban parasite reservoir hosts. In Brazil, indirect fluorescence antibody tests (IFAT) and indirect enzyme linked immunosorbent assay (ELISA) using promastigote extracts are widely used in epidemiological surveys. However, their sensitivity and specificity have often been compromised by the use of complex mixtures of antigens, which reduces their accuracy allowing the maintenance of infected animals that favors transmission to humans. In this context, the use of combinations of defined peptides appears favorable. Therefore, they were tested by combinations of five peptides derived from the previously described Leishmania diagnostic antigens A2, NH, LACK and K39.

METHODOLOGY/PRINCIPAL FINDINGS

Combinations of peptides derived A2, NH, LACK and K39 antigens were used in ELISA with sera from 44 human patients and 106 dogs. Improved sensitivities and specificities, close to 100%, were obtained for both sera of patients and dogs. Moreover, high sensitivity and specificity were observed even for canine sera presenting low IFAT anti-Leishmania antibody titers or from asymptomatic animals.

CONCLUSIONS/SIGNIFICANCE

The use of combinations of B cell predicted synthetic peptides derived from antigens A2, NH, LACK and K39 may provide an alternative for improved sensitivities and specificities for immunodiagnostic assays of VL.

Control of visceral leishmaniasis in latin america-a systematic review

BACKGROUND

While three countries in South Asia decided to eliminate anthroponotic visceral leishmaniasis (VL) by 2015, its control in other regions seems fraught with difficulties. Is there a scope for more effective VL control in the Americas where transmission is zoonotic? We reviewed the evidence on VL control strategies in Latin America-diagnosis, treatment, veterinary interventions, vector control-with respect to entomological and clinical outcomes.

METHODOLOGY/PRINCIPAL FINDINGS

We searched the electronic databases of MEDLINE, LILACS, and the Cochrane Central Register of Controlled Trials, from 1960 to November 2008 and references of selected articles. Intervention trials as well as observational studies that evaluated control strategies of VL in the Americas were included. While the use of rapid diagnostic tests for VL diagnosis seems well established, there is a striking lack of evidence from clinical trials for drug therapy and few well designed intervention studies for control of vectors or canine reservoirs.

CONCLUSION

Elimination of zoonotic VL in the Americas does not seem a realistic goal at this point given the lack of political commitment, gaps in scientific knowledge, and the weakness of case management and surveillance systems. Research priorities and current strategies should be reviewed with the aim of achieving better VL control.

Transmission, reservoir hosts and control of zoonotic visceral leishmaniasis

Zoonotic visceral leishmaniasis (ZVL) caused by Leishmania infantum is an important disease of humans and dogs. Here we review aspects of the transmission and control of ZVL. Whilst there is clear evidence that ZVL is maintained by sandfly transmission, transmission may also occur by non-sandfly routes, such as congenital and sexual transmission. Dogs are the only confirmed primary reservoir of infection. Meta-analysis of dog studies confirms that infectiousness is higher in symptomatic infection; infectiousness is also higher in European than South American studies. A high prevalence of infection has been reported from an increasing number of domestic and wild mammals; updated host ranges are provided. The crab-eating fox Cerdocyon thous, opossums Didelphis spp., domestic cat Felis cattus, black rat Rattus rattus and humans can infect sandflies, but confirmation of these hosts as primary or secondary reservoirs requires further xenodiagnosis studies at the population level. Thus the putative sylvatic reservoir(s) of ZVL remains unknown. Review of intervention studies examining the effectiveness of current control methods highlights the lack of randomized controlled trials of both dog culling and residual insecticide spraying. Topical insecticides (deltamethrin-impregnated collars and pour-ons) have been shown to provide a high level of individual protection to treated dogs, but further community-level studies are needed.

Identification of highly specific and cross-reactive antigens of Leishmania species by antibodies from Leishmania (Leishmania) chagasi naturally infected dogs

The Leishmania species present a genetic homology that ranges from 69 to 90%. Because of this homology, heterologous antigens have been used in the immunodiagnosis and vaccine development against Leishmania infections. In the current work, we describe the identification of species-specific and cross-reactive antigens among several New World Leishmania species, using symptomatic and asymptomatic naturally Leishmania chagasi-infected dog sera. Soluble antigens from five strains of New World Leishmania were separated by electrophoresis in SDS-PAGE and immunoblotted. Different proteins were uniquely recognized in the L. chagasi panel by either symptomatic or asymptomatic dog sera suggesting their use as markers for the progression of disease and diagnosis of the initial (sub-clinical) phase of the infection. Cross-reactive antigens were identified using heterologous antigenic panels (L. amazonensis strains PH8 and BH6, L. guyanensis and L. braziliensis). L. guyanensis panel showed the highest cross-reactivity against L. chagasi specific antibodies, suggesting that proteins from this extract might be suitable for the diagnosis of visceral canine leishmaniasis. Interestingly, the 51 and 97 kDa proteins of Leishmania were widely recognized (77.8% to 100%) among all antigenic panels tested, supporting their potential use for immunodiagnosis. Finally, we identified several leishmanial antigens that might be useful for routine diagnosis and seroepidemiological studies of the visceral canine leishmaniasis.

Methods for diagnosis of canine leishmaniasis and immune response to infection

Canine leishmaniasis (CanL) caused by Leishmania infantum (syn. L. chagasi, in Latin America), which is transmitted by the bite of phlebotomine sand flies, is endemic and affects millions of dogs in Europe, Asia, North Africa and South America. It is an emergent disease in North America. Early detection and treatment of infected animals may be critical in controlling the spread of the disease and is an essential part of human zoonotic visceral leishmaniasis control. The laboratory diagnosis of CanL still poses a challenge, despite progress made in the development of several direct and indirect methods. An effective diagnosis test, apart of being able to confirm a clinical suspicion in a single patient as well as to detect infection in asymptomatic dogs, should have high sensitivity, specificity and reproducibility; it must be simple, easy to perform, non-expensive, feasible in regional laboratories or adaptable for field conditions. Ideally, it should detect all Leishmania-infected dogs, preferentially using non-invasive collection of biological samples. In this paper we review the advantages and shortcomings of the available procedures for CanL diagnosis in the different phases, e.g. pre-patent and patent period of the infection and methods to determine the related immune response.

Canine visceral leishmaniasis: performance of a rapid diagnostic test (Kalazar Detect) in dogs with and without signs of the disease

Current visceral leishmaniasis (VL) control programs in Brazil include the infected dog elimination but, despite this strategy, the incidence of human VL is still increasing. One of the reasons is the long delay between sample collection, analysis, control implementation and the low sensitivity of diagnostic tests. Due to the high prevalence of asymptomatic dogs, the diagnosis of these animals is important considering their vector infection capacity. Hence, a rapid and accurate diagnosis of canine visceral leishmaniasis is essential for an efficient surveillance program. In this study we evaluated the performance of rK39 antigen in an immunochromatographic format to detect symptomatic and asymptomatic Leishmania chagasi infection in dogs and compared the results with those using a crude antigen ELISA. The sensitivity of rK39 dipstick and ELISA were 83% vs. 95%, respectively, while the specificity was both 100%. Our results also demonstrated that the dipstick test was able to detect infected dogs presenting different clinical forms.

Development and evaluation ofLeishmania infantumrK26 ELISA for serodiagnosis of visceral leishmaniasis in Iran

The purpose of this study was to prepare recombinant K26 antigen fromLeishmania infantumand evaluate its performance by enzyme-linked immunosorbent assay (ELISA) test for serodiagnosis of visceral leishmaniasis (VL) in endemic regions of Iran. The results were compared with those obtained by direct agglutination test (DAT) and whole cell ELISA using crude parasite antigen. Of 93 sera from patients with confirmed VL, 90 sera were positive with rK26 ELISA (sensitivity=96·8%), whereas 85 sera were positive with DAT (sensitivity=91·4%) and 89 sera were positive with whole cell ELISA (sensitivity=95·7%). Of 130 subjects who either had other infectious diseases (n=30) or were healthy (n=100), rK26 ELISA were negative in all cases (specificity=100%), whereas DAT were negative in 116 cases (specificity=89·2%) and whole cell ELISA was negative in 114 cases (specificity=87·7%). The results of this study indicate that the rK26 ELISA is more sensitive and specific than conventional methods and could be used for reliable diagnosis of VL caused byLeishmania infantum.

Kinetoplastids: related protozoan pathogens, different diseases

Kinetoplastids are a group of flagellated protozoans that include the species Trypanosoma and Leishmania, which are human pathogens with devastating health and economic effects. The sequencing of the genomes of some of these species has highlighted their genetic relatedness and underlined differences in the diseases that they cause. As we discuss in this Review, steady progress using a combination of molecular, genetic, immunologic, and clinical approaches has substantially increased understanding of these pathogens and important aspects of the diseases that they cause. Consequently, the paths for developing additional measures to control these "neglected diseases" are becoming increasingly clear, and we believe that the opportunities for developing the drugs, diagnostics, vaccines, and other tools necessary to expand the armamentarium to combat these diseases have never been better.

Comparative evaluation of enzyme-linked immunosorbent assays based on crude and recombinant leishmanial antigens for serodiagnosis of symptomatic and asymptomatic Leishmania infantum visceral infections in dogs

The diagnosis of visceral leishmaniasis remains difficult in rural areas where the disease is endemic, and serologic methods still need assessment, as they are not very sensitive for the detection of asymptomatic infectious dogs. Here we present data on the development of enzyme-linked immunosorbent assay (ELISA)-based methods for the detection of antibodies against recombinant leishmanial antigens (namely, the recombinant K26 [rK26] and rK39 antigens from Leishmania infantum and the rA2 protein from Leishmania donovani) in comparison to ELISAs employing crude soluble antigen (CSA). The assays utilized sera from known negative controls (n=25) and clinically asymptomatic (n=50) and symptomatic (n=50) dogs with confirmed L. infantum infections. Additional studies were also done using sera from animals harboring other infections (n=14) for the evaluation of cross-reactivity. Our study indicated that rK26 and rK39 used in ELISAs provided very high sensitivities for the detection of symptomatic dogs (94% and 100%, respectively), followed by CSA (88%) and rA2 (70%). Conversely, rA2 was more sensitive for asymptomatic dogs (88%) than rK39 and rK26 (both 66%) and CSA (30%). Some cross-reactivity in sera from dogs with other infections (Leishmania braziliensis and Leptospira interrogans) was identified, but the rA2 protein provided the greatest specificity (98%). Data further indicate that all three recombinant proteins must be used in parallel to detect essentially all infected dogs. Efforts should be made to develop a cheap and reliable serologic test based on epitope selection from these diagnostic markers for the sensitive detection of L. infantum-infected dogs.

Evaluation of an ELISA rapid device for the serological diagnosis of Leishmania infantum infection in dog as compared with immunofluorescence assay and Western blot

In this study we compared a commercial enzyme linked immunosorbent assay (ELISA) rapid test (Snap CLATK Canine Leishmania Antibody Test Kit, IDEXX-Snap) with indirect immunofluorescence assay (IFA) and Western blot (WB) for the detection of Leishmania infantum antibodies in dogs. In total sera from 234 dogs were collected: 59 positives and 51 doubtful sera (IFA 1:40-1:80) from an L. infantum endemic area and 124 negative sera from a non-endemic area were tested. To evaluate the Snap CLATK's performances on whole blood, blood in EDTA and sera from 37 dogs were tested in parallel with Snap CLATK. Snap CLATK sensitivity and specificity compared to IFA were 91.1% and 99.2%, while compared to WB were 93.4% and 98.3%, respectively. When IFA doubtful sera (titers of 1:40 or 1:80) were tested Snap CLATK, using WB as reference, sensitivity and specificity were 90.9% and 100%, respectively. Moreover, a complete concordance was observed when Snap CLATK rapid assay was carried out on whole blood or sera from 37 dogs. The Snap CLATK has demonstrated simplicity and performance and can be considered a quick and reliable alternative for the diagnosis of L. infantum infection in dogs.