British Red Squirrels Remain the Only Known Wild Rodent Host for Leprosy Bacilli

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.

Shifts in immune responses of an invasive alien species: A test of the evolution of increased competitive ability hypothesis using American Eastern gray squirrels in Italy

Based on the Evolution of Increased Competitive Ability (EICA) hypothesis, a reduced investment in immunity, consequent to parasite loss, could partly explain the success of invasive alien species. We investigated variation in parasite load and immune responses of alien Eastern gray squirrels (Sciurus carolinensis) along the invasion wave of an expanding population. We first verified by fecal analyses that 1) parasite abundance decreased moving from the core towards the invasion front. Next, we used multiple measures of immunity to investigate whether, in response to the lower parasite pressure, individuals at the invasion front 2) dampened their costly inflammatory response, and 3) increased their investment in less expensive acquired immunity. We first explored variation in hematological variables related either to the inflammatory or the acquired response. On a subset of individuals, we carried out ex vivo cell cultures to analyse the basal expression of MHC class II genes and the expression of TNF-α genes in response to an immune challenge. Platelet counts and TNF-α expression suggested higher inflammation in individuals living at the invasion core, whereas parameters associated with an acquired response (lymphocyte counts and MHC II expression by spleen cells), conversely, were higher in squirrels at the front. Overall, our results suggest a shift between different immune strategies along the invasion wave, supporting a reduced investment in costly inflammatory responses and an increased investment in acquired immunity in individuals at the expanding edge of the range, which are subjected to high selective pressures for dispersal and reproduction.

Interactions between native and invasive species: A systematic review of the red squirrel-gray squirrel paradigm

The eastern gray squirrel (Sciurus carolinensis) has been labeled as one of the 100 worst invasive alien species by the IUCN. In Europe, the species has been introduced to Britain, Ireland and Italy, and its subsequent spread has resulted in wide-scale extinction of native Eurasian red squirrels (Sciurus vulgaris) from the areas colonized by the gray squirrel. This replacement of a native by an alien competitor is one of the best documented cases of the devastating effects of biological invasions on native fauna. To understand how this replacement occurs, we present a systematic review of the literature on competition and interactions between red and gray squirrels. We describe the patterns of red and gray squirrel distribution in those parts of Europe where gray squirrels occur and summarize the evidence on the different processes and mechanisms determining the outcome of competition between the native and alien species including the influence of predators and pathogens. Some of the drivers behind the demise of the red squirrel have been intensively studied and documented in the past 30 years, but recent field studies and mathematical models revealed that the mechanisms underlying the red-gray paradigm are more complex than previously thought and affected by landscape-level processes. Therefore, we consider habitat type and multi-species interactions, including host-parasite and predator-prey relationships, to determine the outcome of the interaction between the two species and to better address gray squirrel control efforts.

Mycobacterium leprae in Armadillo Tissues from Museum Collections, United States

We examined armadillos from museum collections in the United States using molecular assays to detect leprosy-causing bacilli. We found Mycobacterium leprae bacilli in samples from the United States, Bolivia, and Paraguay; prevalence was 14.8% in nine-banded armadillos. US isolates belonged to subtype 3I-2, suggesting long-term circulation of this genotype.

Biocultural perspectives of infectious diseases and demographic evolution: Tuberculosis and its comorbidities through history

Anthropologists recognize the importance of conceptualizing health in the context of the mutually evolving nature of biology and culture through the biocultural approach, but biocultural anthropological perspectives of infectious diseases and their impacts on humans (and vice versa) through time are relatively underrepresented. Tuberculosis (TB) has been a constant companion of humans for thousands of years and has heavily influenced population health in almost every phase of cultural and demographic evolution. TB in human populations has been dramatically influenced by behavior, demographic and epidemiological shifts, and other comorbidities through history. This paper critically discusses TB and some of its major comorbidities through history within a biocultural framework to show how transitions in human demography and culture affected the disease-scape of TB. In doing so, I address the potential synthesis of biocultural and epidemiological transition theory to better comprehend the mutual evolution of infectious diseases and humans.

The Presence of Mycobacterium leprae in Wild Rodents

Leprosy is a chronic infection caused by Mycobacterium leprae. There is a lack of data regarding environmental reservoirs, which may represent a serious public health problem in Brazil, especially in the state of Pará, which occupies the fourth position in incidence of cases in the country. Previous studies report evidence of infection occurring among armadillos, mangabei monkeys, and chimpanzees. In the present study, wild animals were captured and tested for the presence of anti-PGL-1 antibodies and M. leprae DNA. Fieldwork was carried out from October to November of 2016 in the cities of Curionópolis and Canaã dos Carajás, southeast of Pará state. Small and medium-sized wild animals were captured using appropriate traps. A total of 15 animals were captured. Sera and viscera fragments were collected and tested by ELISA and PCR methods. The presence of M. leprae DNA was confirmed by sequencing of specific gyrase gene in three animals of two different species, including one Necromys lasiurus (liver sample) and two Proechimys roberti (kidney and liver samples). This unprecedented finding suggests that species other than those previously reported are responsible for maintaining M. leprae in nature.

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.

Mycobacterium lepromatosis as a Second Agent of Hansen's Disease

Mycobacterium lepromatosis was identified as a new species and second causal agent of Hansen's disease (HD, or leprosy) in 2008, 150years after the disease was first attributed to Mycobacterium leprae. M. lepromatosis has been implicated in a small number of HD cases, and clinical aspects of HD caused by M. lepromatosis are poorly characterized. HD is a recognized zoonosis through transmission of M. leprae from armadillos, but the role of M. lepromatosis as a zoonotic agent of HD is unknown. M. lepromatosis was initially associated with diffuse lepromatous leprosy, but subsequent case reports and surveys have linked it to other forms of HD. HD caused by M. lepromatosis has been reported from three endemic countries: Brazil, Myanmar, and Philippines, and three non-endemic countries: Mexico, Malaysia, and United States. Contact with armadillos in Mexico was mentioned in 2/21 M. lepromatosis HD case reports since 2008. M. lepromatosis in animals has been investigated only in non-endemic countries, in squirrels and chipmunks in Europe, white-throated woodrats in Mexico, and armadillos in the United States. To date, there have only been a small number of positive findings in Eurasian red squirrels in Britain and Ireland. A single study of environmental samples found no M. lepromatosis in soil from a Scottish red squirrel habitat. Future studies must focus on endemic countries to determine the true proportion of HD cases caused by M. lepromatosis, and whether viable M. lepromatosis occurs in non-human sources.

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.

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.

Metagenomics of the modern and historical human oral microbiome with phylogenetic studies on Streptococcus mutans and Streptococcus sobrinus

We have recently developed bioinformatic tools to accurately assign metagenomic sequence reads to microbial taxa: SPARSE for probabilistic, taxonomic classification of sequence reads; EToKi for assembling and polishing genomes from short-read sequences; and GrapeTree, a graphic visualizer of genetic distances between large numbers of genomes. Together, these methods support comparative analyses of genomes from ancient skeletons and modern humans. Here, we illustrate these capabilities with 784 samples from historical dental calculus, modern saliva and modern dental plaque. The analyses revealed 1591 microbial species within the oral microbiome. We anticipated that the oral complexes of Socransky et al., which were defined in 1998, would predominate among taxa whose frequencies differed by source. However, although some species discriminated between sources, we could not confirm the existence of the complexes. The results also illustrate further functionality of our pipelines with two species that are associated with dental caries, Streptococcus mutans and Streptococcus sobrinus. They were rare in historical dental calculus but common in modern plaque, and even more common in saliva. Reconstructed draft genomes of these two species from metagenomic samples in which they were abundant were combined with modern public genomes to provide a detailed overview of their core genomic diversity. This article is part of the theme issue 'Insights into health and disease from ancient biomolecules'.

Mycobacterium uberis Infection in the Subcutaneous Tissue of the Radius/Ulna Area of a Cow

Mycobacterium uberis (M. uberis) is a recently described non-tuberculous mycobacterium phylogenetically close to Mycobacterium leprae (M. leprae) and Mycobacterium lepromatosis (M. lepromatosis). This pathogen classically causes nodular thelitis in cattle and goats. Here, we discuss what seems to be the first described case of M. uberis infection in a novel anatomical site, in the proximal or distal position (information not available) of the radius/ulna area of a cow. As this case was discovered in the framework of bovine tuberculosis (bTB) surveillance program in France, this type of infection could interfere with the screening and diagnostic tools employed for bTB.

Molecular epidemiology of leprosy: An update

Molecular epidemiology investigations are notoriously challenging in the leprosy field mainly because the inherent characteristics of the disease as well as its yet uncultivated causative agents, Mycobacterium leprae and M. lepromatosis. Despite significant developments in understanding the biology of leprosy bacilli through genomic approaches, the exact mechanisms of transmission is still unclear and the factors underlying pathological variation of the disease in different patients remain as major gaps in our knowledge about leprosy. Despite these difficulties, the last two decades have seen the development of genotyping procedures based on PCR-sequencing of target loci as well as by the genome-wide analysis of an increasing number of geographically diverse isolates of leprosy bacilli. This has provided a foundation for molecular epidemiology studies that are bringing a better understanding of strain evolution associated with ancient human migrations, and phylogeographical insights about the spread of disease globally. This review discusses the advantages and drawbacks of the main tools available for molecular epidemiological investigations of leprosy and summarizes various methods ranging from PCR-based genotyping to genome-typing techniques. We also describe their main applications in analyzing the short-range and long-range transmission of the disease. Finally, we summarise the current gaps and challenges that remain in the field of molecular epidemiology of leprosy.

Genomic Characterization of Mycobacterium leprae to Explore Transmission Patterns Identifies New Subtype in Bangladesh

Mycobacterium leprae, the causative agent of leprosy, is an unculturable bacterium with a considerably reduced genome (3.27 Mb) compared to homologues mycobacteria from the same ancestry. In 2001, the genome of M. leprae was first described and subsequently four genotypes (1-4) and 16 subtypes (A-P) were identified providing means to study global transmission patterns for leprosy. In order to understand the role of asymptomatic carriers we investigated M. leprae carriage as well as infection in leprosy patients (n = 60) and healthy household contacts (HHC; n = 250) from Bangladesh using molecular detection of the bacterial element RLEP in nasal swabs (NS) and slit skin smears (SSS). In parallel, to study M. leprae genotype distribution in Bangladesh we explored strain diversity by whole genome sequencing (WGS) and Sanger sequencing. In the studied cohort in Bangladesh, M. leprae DNA was detected in 33.3% of NS and 22.2% of SSS of patients with bacillary index of 0 whilst in HHC 18.0% of NS and 12.3% of SSS were positive. The majority of the M. leprae strains detected in this study belonged to genotype 1D (55%), followed by 1A (31%). Importantly, WGS allowed the identification of a new M. leprae genotype, designated 1B-Bangladesh (14%), which clustered separately between the 1A and 1B strains. Moreover, we established that the genotype previously designated 1C, is not an independent subtype but clusters within the 1D genotype. Intraindividual differences were present between the M. leprae strains obtained including mutations in hypermutated genes, suggesting mixed colonization/infection or in-host evolution. In summary, we observed that M. leprae is present in asymptomatic contacts of leprosy patients fueling the concept that these individuals contribute to the current intensity of transmission. Our data therefore emphasize the importance of sensitive and specific tools allowing post-exposure prophylaxis targeted at M. leprae-infected or -colonized individuals.

Reservoirs and transmission routes of leprosy; A systematic review

Leprosy is a chronic infectious disease caused by Mycobacterium leprae (M. leprae) and the more recently discovered Mycobacterium lepromatosis (M. lepromatosis). The two leprosy bacilli cause similar pathologic conditions. They primarily target the skin and the peripheral nervous system. Currently it is considered a Neglected Tropical Disease, being endemic in specific locations within countries of the Americas, Asia, and Africa, while in Europe it is only rarely reported. The reason for a spatial inequality in the prevalence of leprosy in so-called endemic pockets within a country is still largely unexplained. A systematic review was conducted targeting leprosy transmission research data, using PubMed and Scopus as sources. Publications between January 1, 1945 and July 1, 2019 were included. The transmission pathways of M. leprae are not fully understood. Solid evidence exists of an increased risk for individuals living in close contact with leprosy patients, most likely through infectious aerosols, created by coughing and sneezing, but possibly also through direct contact. However, this systematic review underscores that human-to-human transmission is not the only way leprosy can be acquired. The transmission of this disease is probably much more complicated than was thought before. In the Americas, the nine-banded armadillo (Dasypus novemcinctus) has been established as another natural host and reservoir of M. leprae. Anthroponotic and zoonotic transmission have both been proposed as modes of contracting the disease, based on data showing identical M. leprae strains shared between humans and armadillos. More recently, in red squirrels (Sciurus vulgaris) with leprosy-like lesions in the British Isles M. leprae and M. lepromatosis DNA was detected. This finding was unexpected, because leprosy is considered a disease of humans (with the exception of the armadillo), and because it was thought that leprosy (and M. leprae) had disappeared from the United Kingdom. Furthermore, animals can be affected by other leprosy-like diseases, caused by pathogens phylogenetically closely related to M. leprae. These mycobacteria have been proposed to be grouped as a M. leprae-complex. We argue that insights from the transmission and reservoirs of members of the M. leprae-complex might be relevant for leprosy research. A better understanding of possible animal or environmental reservoirs is needed, because transmission from such reservoirs may partly explain the steady global incidence of leprosy despite effective and widespread multidrug therapy. A reduction in transmission cannot be expected to be accomplished by actions or interventions from the human healthcare domain alone, as the mechanisms involved are complex. Therefore, to increase our understanding of the intricate picture of leprosy transmission, we propose a One Health transdisciplinary research approach.

Leprosy is a chronic infectious disease caused by Mycobacterium leprae (M. leprae) and the more recently discovered Mycobacterium lepromatosis (M. lepromatosis). The two leprosy bacilli cause similar stigmatizing pathologic conditions. M. leprae primarily targets the skin and the peripheral nervous system. Currently it is considered a Neglected Tropical Disease. The transmission pathways of M. leprae are not fully understood. Solid evidence exists of an increased risk for individuals living in close contact with leprosy patients, most likely through infectious aerosols, created by coughing and sneezing, but possibly also through direct contact. However, this systematic review underscores that human-to-human transmission is not the only way leprosy can be acquired. Anthroponotic and zoonotic transmission have both been proposed as modes of contracting the disease, based on data showing identical M. leprae strains shared between humans and armadillos. A better understanding of possible animal or environmental reservoirs is needed, because transmission from such reservoirs may partly explain the steady global incidence of leprosy despite effective and widespread multidrug therapy. Reducing transmission cannot be expected from the human healthcare domain alone, as the mechanisms involved are complex. Therefore, we propose a One Health transdisciplinary research approach.