Detection of humoral immunity to mycobacteria causing leprosy in Eurasian red squirrels (Sciurus vulgaris) using a quantitative rapid test

Molecular and Serological Surveillance for Mycobacterium leprae and Mycobacterium lepromatosis in Wild Red Squirrels (Sciurus vulgaris) from Scotland and Northern England

Leprosy is a poverty-associated infectious disease in humans caused by Mycobacterium leprae or M. lepromatosis, often resulting in skin and peripheral nerve damage, which remains a significant public health concern in isolated areas of low- and middle-income countries. Previous studies reported leprosy in red squirrels in the British Isles, despite the fact that autochthonous human cases have been absent for centuries in this region. To investigate the extent of M. leprae and M. lepromatosis presence in wild red squirrels in the northern UK, we analyzed 220 blood/body cavity fluid samples from opportunistically sampled red squirrels (2004-2023) for specific antibodies against phenolic glycolipid-I, a cell wall component specific for these leprosy bacilli. Additionally, we assessed bacillus-derived DNA by real-time PCR (qPCR) in 250 pinnae from the same cohort. M. lepromatosis and M. leprae DNA were detected by qPCR in 20.4% and 0.8% of the squirrels, respectively. No cases of co-detection were observed. Detectable levels of anti-PGL-I antibodies by UCP-LFA were observed in 52.9% of animals with the presence of M. lepromatosis determined by qPCR, and overall in 15.5% of all animals. In total, 22.6% (n = 296) of this UK cohort had at least some exposure to leprosy bacilli. Our study shows that leprosy bacilli persist in red squirrels in the northern UK, emphasizing the necessity for ongoing molecular and serological monitoring to study leprosy ecology in red squirrels, gain insight into potential zoonotic transmission, and to determine whether the disease has a conservation impact on this endangered species.

Development of lateral flow assays to detect host proteins in cattle for improved diagnosis of bovine tuberculosis

Bovine tuberculosis (bTB), caused by Mycobacterium bovis (M. bovis) infection in cattle, is an economically devastating chronic disease for livestock worldwide. Efficient disease control measures rely on early and accurate diagnosis using the tuberculin skin test (TST) and interferon-gamma release assays (IGRAs), followed by culling of positive animals. Compromised performance of TST and IGRA, due to BCG vaccination or co-infections with non-tuberculous mycobacteria (NTM), urges improved diagnostics. Lateral flow assays (LFAs) utilizing luminescent upconverting reporter particles (UCP) for quantitative measurement of host biomarkers present an accurate but less equipment- and labor-demanding diagnostic test platform. UCP-LFAs have proven applications for human infectious diseases. Here, we report the development of UCP-LFAs for the detection of six bovine proteins (IFN-γ, IL-2, IL-6, CCL4, CXCL9, and CXCL10), which have been described by ELISA as potential biomarkers to discriminate M. bovis infected from naïve and BCG-vaccinated cattle. We show that, in line with the ELISA data, the combined PPDb-induced levels of IFN-γ, IL-2, IL-6, CCL4, and CXCL9 determined by UCP-LFAs can discriminate M. bovis challenged animals from naïve (AUC range: 0.87-1.00) and BCG-vaccinated animals (AUC range: 0.97-1.00) in this cohort. These initial findings can be used to develop a robust and user-friendly multi-biomarker test (MBT) for bTB diagnosis.

Host biomarker-based quantitative rapid tests for detection and treatment monitoring of tuberculosis and COVID-19

Diagnostic services for tuberculosis (TB) are not sufficiently accessible in low-resource settings, where most cases occur, which was aggravated by the COVID-19 pandemic. Early diagnosis of pulmonary TB can reduce transmission. Current TB-diagnostics rely on detection of Mycobacterium tuberculosis (Mtb) in sputum requiring costly, time-consuming methods, and trained staff. In this study, quantitative lateral flow (LF) assays were used to measure levels of seven host proteins in sera from pre-COVID-19 TB patients diagnosed in Europe and latently Mtb-infected individuals (LTBI), and from COVID-19 patients and healthy controls. Analysis of host proteins showed significantly lower levels in LTBI versus TB (AUC:0 · 94) and discriminated healthy individuals from COVID-19 patients (0 · 99) and severe COVID-19 from TB. Importantly, these host proteins allowed treatment monitoring of both respiratory diseases. This study demonstrates the potential of non-sputum LF assays as adjunct diagnostics and treatment monitoring for COVID-19 and TB based on quantitative detection of multiple host biomarkers.

Detection of anti-M. leprae antibodies in healthy children in China: A systematic review of Chinese literature

Leprosy is an infectious disease caused by Mycobacterium leprae (M. leprae) that mainly involves the skin and peripheral nerves, causing lifelong deformities and social stigma. As evident from the practically stable number of new cases reported worldwide during the past decade, transmission is still ongoing. On route to leprosy elimination, an appropriate tool is needed to monitor M. leprae transmission. M. leprae-specific antibodies indicate infection with M. leprae, but do not differentiate between present and past infection. Nevertheless, detection of M. leprae infection in young children per definition indicates recent infection. Hence, seroprevalence in young children can be used to monitor recent M. leprae transmission. Despite having eliminated leprosy in most parts of the country, studies on transmission conducted in China are not sufficiently reported in the English literature. Therefore, we performed a systematic review of Chinese literature describing serological studies in healthy children in (former) leprosy endemic areas in China, available in the Chinese databases: China National Knowledge Infrastructure (CNKI), China Science and Technology Journal Database (VIP), and Wanfang Database. From the 710 articles identified in these three Chinese databases, only four full-text articles fulfilled all inclusion criteria regarding sufficiently detailed descriptions of anti-M. leprae antibodies in healthy children. Two additional papers were identified through snowballing, resulting in a total of six articles considered for this review reporting quantitative serological data from three Chinese provinces between 1987 and 2003. All studies used ELISAs to quantify antibody levels. Seroprevalence in healthy children ranged from 7.93% (Yunnan) to 32.35% (Jiangsu). If the same method was used (in Jiangsu), direct comparison of studies at different time points indicated that decrease in disease prevalence (0.28 to 0.16 per 100,000) or new case detection rate (2.6 to 1.0 per 100,000) from 1987-1991 corresponded to decrease in anti-M. leprae antibody seroprevalence (30.86% to 22.61%) in healthy children. Thus, these findings are consistent with the previous finding that anti-M. leprae antibody seroprevalence in young children represents a surrogate indicator to monitor transmission.

CLINICAL PROGRESSION OF LEPROSY IN EURASIAN RED SQUIRRELS (SCIURUS VULGARIS) IN A NATURALLY INFECTED WILD POPULATION

Leprosy has been described in Eurasian red squirrel (Sciurus vulgaris; ERS) carcasses since 2014. Studies of ERS carcasses have not provided information about incubation or disease progression in this host but have provided important insights into pathogen presence and distribution throughout the United Kingdom. Here we present field study data on 31 live ERS from an island population naturally infected with Mycobacterium leprae that were assessed longitudinally over a 2-yr time period. Clinical assessment, serologic (anti-phenolic glycolipid-I antibody [αPGL-I] detection) and molecular methods (polymerase chain reaction) were used to diagnose and categorize ERS at each assessment as a leprosy case, a leprosy suspect, colonized by M. leprae, or a contact ERS. Eight ERS (25.8%) were identified as leprosy cases: four at initial assessment, two at 6 mon and two at 24 mon after initial assessment. One ERS was categorized a leprosy suspect when it developed typical lesions 12 mon after initial assessment, despite negative serologic and molecular test results at this time, though M. leprae DNA had been isolated during the initial assessment. Seven ERS (22.6%) were categorized as colonized and of these, six were reassessed but did not develop clinical signs of leprosy within 6 (n = 2), 12 (n = 3), and 18 (n = 1) mon. Most (48.4%, n = 15) were categorized as contact ERS. Progression of leprosy lesions varied between ERS, but always increased in severity over time and was paralleled with increased antibody response. Based on our dataset, we propose the hypotheses: 1) leprosy in ERS is a chronic, slowly progressing disease in this species, similar to that described for other hosts; 2) lesions can undergo repeated ulceration-healing cycles; and 3) in some instances M. leprae DNA and αPGL-I antibodies are detectable before the onset of clinical signs of disease. Future studies addressing the progression of leprosy in ERS should follow affected animals over a longer time period and include tissue samples to pair molecular diagnostics with serologic results.

Quantitative Rapid Test for Detection and Monitoring of Active Pulmonary Tuberculosis in Nonhuman Primates

Nonhuman primates (NHPs) are relevant models to study the pathogenesis of tuberculosis (TB) and evaluate the potential of TB therapies, but rapid tools allowing diagnosis of active pulmonary TB in NHPs are lacking. This study investigates whether low complexity lateral flow assays utilizing upconverting reporter particles (UCP-LFAs) developed for rapid detection of human serum proteins can be applied to detect and monitor active pulmonary TB in NHPs. UCP-LFAs were used to assess serum proteins levels and changes in relation to the MTB challenge dosage, lung pathology, treatment, and disease outcome in experimentally MTB-infected macaques. Serum levels of SAA1, IP-10, and IL-6 showed a significant increase after MTB infection in rhesus macaques and correlated with disease severity as determined by pathology scoring. Moreover, these biomarkers could sensitively detect the reduction of bacterial levels in the lungs of macaques due to BCG vaccination or drug treatment. Quantitative measurements by rapid UCP-LFAs specific for SAA1, IP-10, and IL-6 in serum can be utilized to detect active progressive pulmonary TB in macaques. The UCP-LFAs thus offer a low-cost, convenient, and minimally invasive diagnostic tool that can be applied in studies on TB vaccine and drug development involving macaques.

Detection and Monitoring of Mycobacterium leprae Infection in Nine Banded Armadillos (Dasypus novemcinctus) Using a Quantitative Rapid Test

Leprosy is an infectious disease caused by Mycobacterium leprae with tropism for skin and peripheral nerves. Incessant transmission in endemic areas is still impeding elimination of leprosy. Although detection of M. leprae infection remains a challenge in asymptomatic individuals, the presence of antibodies specific for phenolglycolipid-I (PGL-I) correlate with bacterial load. Therefore, serosurveillance utilizing field-friendly tests detecting anti-PGL-I antibodies, can be applied to identify those who may transmit bacteria and to study (reduction of) M. leprae transmission. However, serology based on antibody detection cannot discriminate between past and present M. leprae infection in humans, nor can it detect individuals carrying low bacillary loads. In humans, anti-PGL-I IgM levels are long-lasting and usually detected in more individuals than anti-PGL-I IgG levels. Inherent to the characteristically long incubation time of leprosy, IgM/IgG relations (antibody kinetics) in leprosy patients and infected individuals are not completely clear. To investigate the antibody response directly after infection, we have measured antibody levels by ELISA, in longitudinal samples of experimentally M. leprae infected, susceptible nine-banded armadillos (Dasypus novemcinctus). In addition, we assessed the user- and field-friendly, low-cost lateral flow assay (LFA) utilizing upconverting reporter particles (UCP), developed for quantitative detection of human anti-PGL-I IgM (UCP-LFA), to detect treatment- or vaccination-induced changes in viable bacterial load. Our results show that serum levels of anti-PGL-I IgM, and to a lesser extent IgG, significantly increase soon after experimental M. leprae infection in armadillos. In view of leprosy phenotypes in armadillos, this animal model can provide useful insight into antibody kinetics in early infection in the various spectral forms of human leprosy. The UCP-LFA for quantitative detection of anti-PGL-I IgM allows monitoring the efficacy of vaccination and rifampin-treatment in the armadillo leprosy model, thereby providing a convenient tool to evaluate the effects of drugs and vaccines and new diagnostics.

Detection of anti-M. leprae antibodies in children in leprosy-endemic areas: A systematic review

BACKGROUND

Leprosy elimination primarily targets transmission of Mycobacterium leprae which is not restricted to patients' households. As interruption of transmission is imminent in many countries, a test to detect infected asymptomatic individuals who can perpetuate transmission is required. Antibodies directed against M. leprae antigens are indicative of M. leprae infection but cannot discriminate between active and past infection. Seroprevalence in young children, however, reflects recent M. leprae infection and may thus be used to monitor transmission in an area. Therefore, this literature review aimed to evaluate what has been reported on serological tests measuring anti-M. leprae antibodies in children without leprosy below the age of 15 in leprosy-endemic areas.

METHODS AND FINDINGS

A literature search was performed in the databases Pubmed, Infolep, Web of Science and The Virtual Health Library. From the 724 articles identified through the search criteria, 28 full-text articles fulfilled all inclusion criteria. Two additional papers were identified through snowballing, resulting in a total of 30 articles reporting data from ten countries. All serological tests measured antibodies against phenolic glycolipid-I or synthetic derivatives thereof, either quantitatively (ELISA or UCP-LFA) or qualitatively (ML-flow or NDO-LID rapid test). The median seroprevalence in children in endemic areas was 14.9% and was stable over time if disease incidence remained unchanged. Importantly, seroprevalence decreased with age, indicating that children are a suitable group for sensitive assessment of recent M. leprae infection. However, direct comparison between areas, solely based on the data reported in these studies, was impeded by the use of different tests and variable cut-off levels.

CONCLUSIONS

Quantitative anti-PGL-I serology in young children holds promise as a screening test to assess M. leprae infection and may be applied as a proxy for transmission and thereby as a means to monitor the effect of (prophylactic) interventions on the route to leprosy elimination.

DIAGNOSING AND CATEGORIZING LEPROSY IN LIVE EURASIAN RED SQUIRRELS (SCIURUS VULGARIS) FOR MANAGEMENT, SURVEILLANCE, AND TRANSLOCATION PURPOSES

The presence of Mycobacterium lepromatosis and Mycobacterium leprae in Eurasian red squirrel (Sciurus vulgaris, ERS) carcasses throughout the British Isles, and leprosy as a disease, have recently been reported using histological and molecular diagnostic methods. In 2016, the first longitudinal study of ERS affected by leprosy was initiated. One of the main challenges was the reliable diagnosis of leprosy in live ERS, which is important for (a) welfare and case management and (b) surveillance or pretranslocation screening efforts. We explored diagnostic methods ranging from detailed clinical assessment and informative categorization of observed lesions, thermal imaging, serology (antiphenolic glycolipid-I antibody [αPGL-I] detection) to molecular methods (polymerase chain reaction [PCR]). For PCR the ear was established as the optimal sampling site. Based on the experiences from this 2-yr study we propose an objective categorization system for clinical lesions and a diagnostic framework for the combination of the diagnostic tools we found to be effective in live ERS: clinical assessment, αPGL-I serology, and PCR. Thermal imaging did not offer additional information for leprosy diagnostics in ERS. We propose an amended definition of leprosy lesions in ERS as "skin areas of local hair loss, in which a firm-rubbery, glossy swelling develops, that may ulcerate" and standardized terminology for describing ERS leprosy status. The information presented forms the basis of a consistent, reliable diagnostic and reporting system for leprosy cases in ERS.

Fatal exudative dermatitis in island populations of red squirrels (Sciurus vulgaris): spillover of a virulent Staphylococcus aureus clone (ST49) from reservoir hosts

Fatal exudative dermatitis (FED) is a significant cause of death of red squirrels (Sciurus vulgaris) on the island of Jersey in the Channel Islands where it is associated with a virulent clone of Staphylococcus aureus, ST49. S. aureus ST49 has been found in other hosts such as small mammals, pigs and humans, but the dynamics of carriage and disease of this clone, or any other lineage in red squirrels, is currently unknown. We used whole-genome sequencing to characterize 228 isolates from healthy red squirrels on Jersey, the Isle of Arran (Scotland) and Brownsea Island (England), from red squirrels showing signs of FED on Jersey and the Isle of Wight (England) and a small number of isolates from other hosts. S. aureus was frequently carried by red squirrels on the Isle of Arran with strains typically associated with small ruminants predominating. For the Brownsea carriage, S. aureus was less frequent and involved strains associated with birds, small ruminants and humans, while for the Jersey carriage S. aureus was rare but ST49 predominated in diseased squirrels. By combining our data with publicly available sequences, we show that the S. aureus carriage in red squirrels largely reflects frequent but facile acquisitions of strains carried by other hosts sharing their habitat ('spillover'), possibly including, in the case of ST188, humans. Genome-wide association analysis of the ruminant lineage ST133 revealed variants in a small number of mostly bacterial-cell-membrane-associated genes that were statistically associated with squirrel isolates from the Isle of Arran, raising the possibility of specific adaptation to red squirrels in this lineage. In contrast there is little evidence that ST49 is a common carriage isolate of red squirrels and infection from reservoir hosts such as bank voles or rats, is likely to be driving the emergence of FED in red squirrels.

Synthetic Phenolic Glycolipids for Application in Diagnostic Tests for Leprosy

Point-of-care (POC) diagnostic tests for the rapid detection of individuals infected with Mycobacterium leprae, the causative pathogen of leprosy, represent efficient tools to guide therapeutic and prophylactic treatment strategies in leprosy control programs, thus positively contributing to clinical outcome and reducing transmission of this infectious disease. Levels of antibodies directed against the M. leprae-specific phenolic glycolipid I (PGL-I) closely correlate with an individual's bacterial load and a higher risk of developing leprosy. We describe herein the assembly of a set of PGL glycans carrying the characteristic phenol aglycon and featuring different methylation patterns. The PGL trisaccharides were applied to construct neoglycoproteins that were used to detect anti-PGL IgM antibodies in leprosy patients. ELISAs and quantitative lateral-flow assays based on up-converting nanoparticles (UCP-LFAs) showed that the generated PGL-I and PGL-II trisaccharide neoglycoconjugates can be applied for the detection of anti M. leprae IgM antibodies in POC tests.

Bacterial Pathogens and Symbionts Harboured by Ixodes ricinus Ticks Parasitising Red Squirrels in the United Kingdom

Red squirrels (Sciurus vulgaris) are native to most of Eurasia; in much of the United Kingdom, they have been supplanted by the non-native grey squirrel, and are considered an endangered species. Very little is known about the range of tick-borne pathogens to which UK red squirrels are exposed. As part of trap-and-release surveys examining prevalence of Mycobacterium spp. in red squirrel populations on two UK islands, Ixodes ricinus ticks were removed from squirrels and PCR screened for Borrelia spp., intracellular arthropod-borne bacteria and the parasitic wasp Ixodiphagus hookeri. At both sites, the most commonly encountered tick-transmitted bacterium was Borrelia burgdorferi sensu lato (overall minimum prevalence 12.7%), followed by Anaplasma phagocytophilum (overall minimum prevalence 1.6%). Single ticks infected with Spiroplasma were found at both sites, and single ticks infected with Borrelia miyamotoi or an Ehrlichia sp. at one site. Ticks harbouring Wolbachia (overall minimum prevalence 15.2%) were all positive for I. hookeri. Our study shows that UK red squirrels are potentially exposed to a variety of bacterial pathogens via feeding ticks. The effects on the health and survival of this already vulnerable wildlife species are unknown, and further studies are needed to evaluate the threat posed to red squirrels by Borrelia and other tick-borne pathogens.

Susceptibility and resistance in leprosy: Studies in the mouse model

Leprosy is a chronic granulomatous infectious disease caused by the pathogen, Mycobacterium leprae, and the more recently discovered, M. lepromatosis. Described in 1873, M. leprae was among the first microorganisms to be proposed as a cause of a human infectious disease. As an obligate intracellular bacterium, it has still not thus far been reproducibly cultivated in axenic medium or cell cultures. Shepard's mouse footpad assay, therefore, was truly a breakthrough in leprosy research. The generation of immunosuppressed and genetically engineered mice, along with advances in molecular and cellular techniques, has since offered more tools for the study of the M. leprae–induced granuloma. While far from perfect, these new mouse models have provided insights into the immunoregulatory mechanisms responsible for the spectrum of this complex disease.

Lack of evidence for the presence of leprosy bacilli in red squirrels from North-West Europe

Leprosy is a human infectious disease caused by Mycobacterium leprae or Mycobacterium lepromatosis that can also occur in animals and even manifest as zoonosis. Recently, both mycobacteria were detected in red squirrels (Sciurus vulgaris) from the British Isles. To further explore the presence of leprosy bacilli in North-West Europe, we screened Belgian and Dutch squirrels. Tissue samples from 115 animals tested by qPCR were negative for both pathogens. No molecular or pathological evidence was found of the presence of these zoonotic pathogens in North-West Europe.