Polymerase chain reaction using conjunctival swab samples for detecting Leishmania DNA in dogs

A review of non-invasive samples and tools in kala-azar diagnosis and test of cure

The recurrence of visceral leishmaniasis (VL), also called kala-azar (KA), in endemic regions of tropical countries like India, is primarily attributed to asymptomatic VL, post-kala azar dermal leishmaniasis (PKDL), and human immunodeficiency virus (HIV) co-infection. To effectively manage VL cases and elimination targets, an early and rapid diagnosis as well as accurate field surveillance is highly essential. The traditional sampling methods like bone marrow (BM), spleen, and lymph node (LN) tissue aspirations are invasive, painful, tedious, and prone to nosocomial infections, require skilled persons and hospital facilities, and are not feasible in rural areas. Therefore, there is an urgent requirement for the adoption of a patient-friendly, non-invasive, non-hospitalized sampling procedure that ensures an effective VL diagnosis. This review aims to meticulously evaluate the most recent scientific research that focuses on the precision, feasibility, and applicability of non-invasive sampling (NIS) and techniques for the diagnosis and test of cure of VL, particularly in resource-limited settings. Apart from that, the non-invasive techniques (NIT) that have shown promising results while monitoring VL treatment response and relapse are also reviewed. The limitations associated with NIT and possible improvements in this regard are discussed as well to improve the diagnosis and management of VL.

Sensitivity of PCR in conjunctival swab samples for the diagnosis of canine visceral leishmaniasis: a systematic review and meta-analysis

To compare the sensitivity of conjunctival swab (CS) and conventional samples (blood, spleen, liver, lymphoid and cutaneous tissue) in the diagnosis of canine visceral leishmaniasis (CVL) by polymerase chain reaction (PCR), a systematic review and meta-analysis was carried out using PubMed, Science Direct, Scopus, Web of Science, VHL/BVS (Virtual Health Library), CAPES, and Scielo databases. Articles published from 2002 to 2022 were considered and the review was updated in Jul 2023. From the total of 371 identified studies, 8 met all the eligibility criteria and were included in this review. Data from 658 CVL-positive dogs and 2541 PCR results were considered. Using a random effect model, data on the sensitivity of the test was compared between intervention (CS samples) and comparison (all the other samples) groups. Overall, the use of CS in the PCR diagnosis of CVL produced 12% higher sensitivity (p=0.013) in the test than all the other samples in combination. The animals' clinical condition did not influence (p>0.142) this overall result. However, when CS was individually compared to each of the conventional samples, the consistent result was observed (p=0.012) only in the CS versus bone marrow comparison. Given their rapid acquisition, minimal invasiveness, and lower cost relative to conventional samples, CS samples present a promising alternative for the molecular diagnosis of CVL.

Leishmania V. braziliensis infection in asymptomatic domestic animals within an endemic region in the Northeast of Brazil

Background:

American cutaneous leishmaniasis is a commonly neglected, vector-borne tropical parasitic disease that is a major public health concern in Brazil. Leishmania (Viannia) braziliensis is the main species associated with the disease. Accurate diagnosis is based on epidemiological surveillance, clinical assessment, and laboratory testing. Leishmania (V.) braziliensis has been detected in several wild and synanthropic mammals. Their epidemiological role has not been entirely elucidated. This study aimed to assess potential L. braziliensis infections in asymptomatic domestic animals, by molecular and serological testing in endemic areas, in the metropolitan region of Recife.

Methods:

Blood samples and conjunctival fluids were collected from 232 animals (canids, felids, equines, and caprines) for the detection of L. braziliensis using molecular tests (conventional and real-time polymerase chain reaction [PCR and qPCR]). For immunological detection, blood samples from 115 dogs were assessed using enzyme-linked immunosorbent assay.

Results:

Real-time quantitative PCR showed positive results for blood and conjunctival samples in all investigated species. The results of the blood and conjunctival samples were 68.2% and 26.9% in Canis familiaris, 100% and 41.7% in Felis catus, 77.3% and 30.8% in Equus caballus/Equus asinus, and 50% and 33.3% in Capra hircus samples, respectively.

Conclusions:

Results from this study adds valuable information to our understanding of the role of asymptomatic domestic animals, L. braziliensis life cycle, and American cutaneous leishmaniasis in Northeast Brazil.

Application Progress of High-Throughput Sequencing in Ocular Diseases

Ocular diseases affect multiple eye parts and can be caused by pathogenic infections, complications of systemic diseases, genetics, environment, and old age. Understanding the etiology and pathogenesis of eye diseases and improving their diagnosis and treatment are critical for preventing any adverse consequences of these diseases. Recently, the advancement of high-throughput sequencing (HTS) technology has paved wide prospects for identifying the pathogenesis, signaling pathways, and biomarkers involved in eye diseases. Due to the advantages of HTS in nucleic acid sequence recognition, HTS has not only identified several normal ocular surface microorganisms but has also discovered many pathogenic bacteria, fungi, parasites, and viruses associated with eye diseases, including rare pathogens that were previously difficult to identify. At present, HTS can directly sequence RNA, which will promote research on the occurrence, development, and underlying mechanism of eye diseases. Although HTS has certain limitations, including low effectiveness, contamination, and high cost, it is still superior to traditional diagnostic methods for its efficient and comprehensive diagnosis of ocular diseases. This review summarizes the progress of the application of HTS in ocular diseases, intending to explore the pathogenesis of eye diseases and improve their diagnosis.

Conjunctival Swab Real Time-PCR in Leishmania infantum Seropositive Dogs: Diagnostic and Prognostic Values

Simple Summary

This 10-month-long study describes how conjunctival swab (CS) real time-PCR (qPCR) failed to be a useful diagnostic and prognostic test for canine leishmaniosis (CanL). From the beginning of the study (October 2020), a limited number of Leishmania infantum seropositive dogs remained CS qPCR positive in August 2021, and none of them developed an active CanL. Therefore, the detection of L. infantum kDNA by qPCR, even highly sensitive, may be considered “a random” if not accompanied by a significant clinical score for CanL and/or other direct diagnostic tests positivity. Hence, in seropositive dogs with CS qPCR positivity, sampling time and season variability of results should be considered. In this scenario, testing other significant biological samples (e.g., lymph node, bone marrow, and spleen), although invasive, is strongly advised.

Abstract

Conjunctival swabs (CS) are the most promising non-invasive samples for the diagnosis and the regular screening of Leishmania infantum infection in dogs although knowledge on their diagnostic performance is still inconclusive. This study evaluates CS real time-PCR (qPCR) analysis for the diagnosis of canine leishmaniosis (CanL) and its prognostic value in seropositive dogs from an endemic area. In October 2020 (T0), 26 dogs were enrolled, divided in two groups according to anti-L. infantum antibody titres (n = 13, group low titre (LT) and n = 13, group high titre (HT)), and followed-up in August 2021. At both timepoints, animals underwent clinical examination, complete blood count and biochemical analyses, and serological (indirect fluorescent antibody test) and molecular (CS and peripheral blood qPCR) testing. At T0, 10 out of 26 enrolled dogs were positive at CS qPCR, with the number of positive animals significantly higher in group HT than in LT. After 10 months, only 5 out of 21 dogs that completed the trial still tested CS qPCR positive, and none of them developed an active CanL based on clinical score and antibody titre. None of the dogs required any leishmanicidal and/or leishmaniostatic treatments. This prospective study showed unsatisfying diagnostic and prognostic performances of CS qPCR analysis in L. infantum seropositive asymptomatic dogs from an endemic area.