Serological and molecular detection of infection with Mycobacterium leprae in Brazilian six banded armadillos (Euphractus sexcinctus)

Leprosy was recognized as a zoonotic disease, associated with nine-banded armadillos (Dasypus novemcinctus) in the Southern United States of America in 2011. In addition, there is growing evidence to support a role for armadillos in zoonotic leprosy in South America. The current study evaluated twenty specimens of the six-banded armadillo (Euphractus sexcinctus), collected from rural locations in the state of Rio Grande do Norte (RN), Brazil for evidence of infection with Mycobacterium leprae. Serum was examined using two "in-house" enzyme-linked immunosorbent assays (ELISAs) and via two commercially available (ML flow and NDO-LID®) immunochromatographic lateral flow (LF) tests, for detection of the PGL-I and/or LID-1 antigens of the bacterium. The presence of M. leprae DNA in liver tissue was examined using the multi-copy, M. leprae-specific repetitive element (RLEP), as target in conventional and nested PCR assays. Molecular and anti-PGL-I-ELISA data indicated that 20/20 (100 %) of the armadillos were infected with M. leprae. The corresponding detection levels recorded with the LF tests were 17/20 (85 %) and 16/20 (85 %), for the NDO-LID® and ML flow tests, respectively. Our results indicate that, in common with D. novemcinctus, six banded armadillos (a species hunted and reared as a food-source in some regions of Brazil, including RN), represent a potential reservoir of M. leprae and as such, their role in a possible zoonotic cycle of leprosy within Brazil warrants further investigation.

Expression and characterization of recombinant interferon gamma (IFN-gamma) from the nine-banded armadillo (Dasypus novemcinctus) and its effect on Mycobacterium leprae-infected macrophages

Armadillos (Dasypus novemcinctus) manifest the full histopathological spectrum of leprosy, and are hosts of choice for in vivo propagation of Mycobacterium leprae. Though potentially useful as a model of leprosy pathogenesis, few armadillo-specific reagents exist. We have identified a region of high homology to the interferon gamma (IFN-gamma) of other mammals within the recently published armadillo whole genomic sequence. cDNA was made from ConA-stimulated armadillo peripheral blood mononuclear cells (PBMC), amplified, and cloned into a pET expression vector for transformation and over-expression in Escherichia coli. The recombinant protein (rDnIFN-gamma) was characterized by western blot and its biological function confirmed with bioassays including intracellular killing of Toxoplasma gondii and induction of indoleamine 2, 3-dioxygenase activity. In using rIFN-gamma to activate macrophages from mice, humans or armadillos, similar to humans, rIFN-gamma-activated armadillo MPhi did not produce nitrite and or inhibit the viability of M. leprae in vitro. Conversely, murine rIFN-gamma-activated mouse MPhi produced high levels of nitrite and killed intracellular M. leprae in vitro. These data indicate that the response of armadillo MPhi to rDnIFN-gamma is similar to that which occurs in humans, and demonstrates a potentially important value of the armadillo as a model in leprosy research.

The continuing challenges of leprosy

Leprosy is best understood as two conjoined diseases. The first is a chronic mycobacterial infection that elicits an extraordinary range of cellular immune responses in humans. The second is a peripheral neuropathy that is initiated by the infection and the accompanying immunological events. The infection is curable but not preventable, and leprosy remains a major global health problem, especially in the developing world, publicity to the contrary notwithstanding. Mycobacterium leprae remains noncultivable, and for over a century leprosy has presented major challenges in the fields of microbiology, pathology, immunology, and genetics; it continues to do so today. This review focuses on recent advances in our understanding of M. leprae and the host response to it, especially concerning molecular identification of M. leprae, knowledge of its genome, transcriptome, and proteome, its mechanisms of microbial resistance, and recognition of strains by variable-number tandem repeat analysis. Advances in experimental models include studies in gene knockout mice and the development of molecular techniques to explore the armadillo model. In clinical studies, notable progress has been made concerning the immunology and immunopathology of leprosy, the genetics of human resistance, mechanisms of nerve injury, and chemotherapy. In nearly all of these areas, however, leprosy remains poorly understood compared to other major bacterial diseases.

Expression of nine-banded armadillo (Dasypus novemcinctus) interleukin-2 in E. coli

The nine-banded armadillo (Dasypus novemcinctus) is the only immunologically intact animal that regularly develops lepromatous-type leprosy when inoculated with Mycobacterium leprae. However, the ability to exploit this model for understanding the pathogenesis of leprosy has been limited by a lack of suitable immunological reagents. Recently, efforts began to sequence the entire armadillo genome, and this sequence information will help make possible the development of a wide array of new immunological reagents suitable for use with armadillos. Using the available sequence data, a region of high homology to interleukin-2 of other mammals was identified. Primers were designed to amplify the coding region corresponding to the mature peptide and its exact sequence was confirmed. cDNA was made from ConA-stimulated armadillo PBMC. The amplified coding region was sub-cloned into a pET expression vector and transformed into Escherichia coli for over-expression. The subsequent product was characterized by SDS-PAGE and bioassays. Tritiated thymidine incorporation by CTLL-2 and armadillo lymphoblasts confirmed functionality of the recombinant product. The advent of the D. novemcinctus genome sequence and subsequent generation of immunological tools will assist in advancing the armadillo as a translational model for leprosy.

Viable M. leprae as a research reagent

Mycobacterium leprae remain a rare research resource. They cannot be cultivated on artificial media, and the only established means to quantify viability of M. leprae has been by its relative growth in the foot pads of conventional mice (MFP). The MFP method is technically difficult and requires several months to yield results. More effective methods are needed. We examined the association between M. leprae's ability to oxidize 14C-palmitate in axenic culture and the MFP growth results of a large number of suspensions. Oxidative activity was assessed by radiorespirometry (RR) using the Buddemeyer-type biphasic culture vessels containing 7H12 liquid medium and 14C-palmitate, or with commercially prepared BACTEC 12B vessels containing the same medium. The RR results were highly correlated (r = 0.71) with the growth level that each M. leprae suspension achieved by the MFP technique. In using this technique to examine the effects that many common laboratory practices have on M. leprae viability, we found that viability varies markedly between bacillary suspensions derived from different hosts and tissues. The highest viabilities were obtained with bacilli from moderately enlarged nude MFP (< 1 g). Viability tended to be lower among very large nude MFP or long-duration infections and from armadillo tissues. After their harvest from host tissues, leprosy bacilli lost viability quickly. Suspensions stored in 7H12 liquid medium retained < 1% of their viability within 3 weeks of harvest, and freezing bacillary preparations or incubating them at 37 degrees C resulted in nearly an immediate equivalent loss in metabolic activity and viability. M. leprae viability is maintained best when bacilli are stored for only short periods of time at 4 degrees C-33 degrees C. Palmitate oxidation is a rapid, reliable and objective means by which to estimate the viability of M. leprae and can be used effectively as a surrogate for the conventional MFP technique in many studies.

The effect of ultraviolet light radiation on Mycobacterium leprae

Ultraviolet (UV) light is recognized as a potent sterilizing aid, but its relative effectiveness against Mycobacterium leprae has not been shown. We examined the influence of UV on the growth and metabolic activity of M. leprae harvested fresh from foot pads of nude mice. Temporary static suspensions were exposed to timed intervals of UV radiation generated from a fixed source to constitute dosages ranging from 0-12.64 x 10(4) erg/cm2. The metabolic activity of the bacilli was indexed by the oxidation of 14C-palmitate in BACTEC 12-B vials. The long-term effects of irradiation on cell division and growth were assessed by inoculation of BALB/c mouse foot pads. The metabolic activity in BACTEC showed an immediate dose-response-related decline to a maximum of 50% of the control activity after exposure to 6.3 x 10(4) erg/cm2. Mouse foot pad studies showed a similar dose-response pattern. Effective-dose determinations based on metabolic or foot pad data were similar. UV doses of 3.52 x 10(4) erg/cm2 resulted in an average 50% killing, and 7.73 x 10(4) erg/cm2 killed 84% of the M. leprae exposed. This UV sensitivity is similar to that reported for M. tuberculosis. UV sterilization and disinfection practices suitable for M. tuberculosis are likely to be equally effective for M. leprae.

Comparative study of Mitsuda reaction to nude mouse and armadillo lepromin preparations using nine-banded armadillos

In 14 nine-banded armadillos the Mitsuda response to nude mouse-derived lepromin (lepromin-nu/nu) was compared to that of armadillo-derived lepromin (lepromin-A) by injecting the reagents intradermally into either side of the abdomen of the animal and examining the biopsies from the sites after 12 days. The histopathologic responses to both antigens were found to be similar, whether the animal was Mitsuda-negative (lepromatous) or Mitsuda-positive (tuberculoid). It is pointed out that armadillos are good experimental models for leprosy, and their use can replace humans in experimental studies.

Infection of distal peripheral nerves by M. leprae in infected armadillos; an experimental model of nerve involvement in leprosy

Mechanisms of localization of Mycobacterium leprae to the peripheral nerves and of subsequent nerve injury are not understood. No experimental animal model has been available for use in examining the pathogenesis of M. leprae-induced nerve injury. A detailed dissection was, therefore, done of the major peripheral nerves in the extremities of six M. leprae-inoculated armadillos, three of which had developed characteristic disseminated infection. All of the animals with disseminated infection had extensive involvement of the peripheral nerves, increasing in intensity as the nerve was followed distally. No M. leprae were found in the animals without disseminated infection. The degree of infection was greater in epineural tissues than in the intraneural compartment (i.e., Schwann cells) at all levels. The infection of nerves by M. leprae was associated with focal interstitial, mononuclear cell infiltration of involved nerves. These results suggest that: 1) armadillos offer a model for the study of neural involvement in leprosy, since the pattern of neural distribution in susceptible armadillos is comparable to the pattern of nerve involvement in man; 2) early localization of M. leprae may be to the epineural tissues, including lymphatic and vascular structures and extracellular matrix; 3) Schwann cell involvement may be a late event; and 4) mechanisms involving the endothelium of epineural and perineural tissues may be important in the selective localization of M. leprae to peripheral nerves.

Armadillos (Dasypus novemcinctus) as a model to test antileprosy vaccines; a preliminary report

The efficacy of two candidate leprosy vaccines, BCG and a mixture of BCG and killed Mycobacterium leprae, was tested in 62 armadillos caught in the wild. The abilities of the vaccines to convert lepromin-negative armadillos to a positive reaction were compared with a group of control animals. Both vaccines upgraded subsequent lepromin skin-test histopathology. The conversion results parallel the protection values obtained in some BCG vaccine trials against leprosy in humans. Before conducting expensive human trials with new antileprosy vaccines, it would be worthwhile first to evaluate them in the armadillo model.

Comparison of polymerase chain reaction technique with other methods for detection of Mycobacterium leprae in tissues of wild nine-banded armadillos

Thirty, nine-banded armadillos weighing between 3 and 5 kilograms trapped from an area endemic for armadillo leprosy were collected at random; killed, autopsied and examined histopathologically. Also, one of the right inguinal lymph nodes was removed under sterile precautions and examined using PCR, direct smear examination, mouse footpad study, culture in laboratory media and histopathology with a view to detecting Mycobacterium leprae. Blood was collected at death and tested for IgM antibodies to PGL-1. According to the PCR study of the inguinal lymph nodes 16 of 30 armadillos (53.3%) had evidence of M. leprae. Significant levels of IgM antibodies to PGL-1 and identifiable lepromatous granuloma in inguinal lymph nodes were found in 2 animals (6.7%) with advanced disseminated disease. The prevalence of generalized leprosy according to autopsy study was 13.3% and according to histopathological examination of ear tissue 3.3%. The presence of M. leprae in the tissues evoked no special tissue reaction in the early stages. The pattern of spread of the disease in 2 animals closely resembled that found in experimental animals infected intracutaneously. Initiation of infection by inoculation of M. leprae through thorn pricks remains a distinct possibility.

Seasonal and spatial trends in the detectability of leprosy in wild armadillos

A survey for leprosy among 565 armadillos from Louisiana and Texas found IgM antibodies to the phenolic glycolipid-1 antigen of Mycobacterium leprae in 16% of the animals. There were no geographic trends in the distribution of prevalence rates between the sites and the disease probably has a much greater range. Repeat observations in one location showed significant seasonal variations in the observable antibody prevalence rate, but the yearly average remained similar. Infected armadillos tended to be heavier, and the females usually had plasma progesterone concentrations indicative of sexual maturity. Using these characteristics to stratify the populations into adult and sub-adult cohorts, variations in the observable leprosy prevalence rate were seen to be proportional to changes in the age structure of the populations. Leprosy appears to be maintained in steady state within some regions, and nearly a third of the adult armadillos in Louisiana and Texas harbour M. leprae.

Early infection with M. leprae and antibodies to phenolic glycolipid-I in the nine-banded armadillo

Nine-banded armadillos were intravenously infected with 10(9) M. leprae. IgM antibodies to PGL-I were evaluated three times during the six months before and every two months after the infection. A thorough autopsy examination was done on animals that died or were sacrificed at intervals of 3, 4, 6, 12, 15 and 18 months after the infection. Three animals which had acquired the infection in the wild and one experimentally infected animal showed significant increases in antibody levels corresponding to their high bacterial load. In the other five experimentally infected animals, M. leprae infection was established in the cells of the reticulo endothelial system (RES) long before the IgM antibody levels to PGL-I became positive. It is possible that in human leprosy also M. leprae may enter and multiply in the RES initiating antibody production during the incubation period before clinical disease with neuritis becomes manifest.

Antibodies to the phenolic glycolipid-1 antigen for epidemiologic investigations of enzootic leprosy in armadillos (Dasypus novemcinctus)

Other than man, nine-banded armadillos (Dasypus novemcinctus) are the only known natural hosts of leprosy with high rates of disease. The origin, range and risk of their infection is not yet clear and a better description of the rate of leprosy over the armadillo's range is needed. Both histopathological examination of armadillo ear tissues and serologic screening for IgM antibodies to the phenolic glycolipid-1 (PGL-1) antigen of Mycobacterium leprae are good relative indices of enzootic prevalence. A survey of 216 armadillos from Louisiana and Florida detected infection only among Louisiana animals. Average antibody prevalence (12.5%) was five times higher than the fully disseminated disease rate described histopathologically (2.7%). The differences in antibody and histopathological prevalence are due to the sensitivity of the methods for detecting early infection. Histopathological examinations describe an advanced disease. The higher antibody prevalence of wild armadillos is not likely to be the result of false positive serologies from self-healing infections or other casual encounters with M. leprae as might be mimicked by lepromin injection. The environmental reservoir of M. leprae represented by infected armadillos is greater than could be previously estimated.

Surveillance for naturally acquired leprosy in a nine-banded armadillo population

Samples from 77 nine-banded armadillos (Dasypus novemcinctus) inhabiting a 16.7 km portion of the East Atchafalaya River Levee, Point Coupee Parish, Louisiana, were serologically tested and/or histopathologically examined for evidence of naturally acquired leprosy. Five of 67 (7.5%) armadillos tested sero-positive with ELISA test for IGM class antibodies to the phenolic-glycolipid-1 antigen of Mycobacterium leprae. One of 74 (1.3%) was histopathologically positive as determined by presence of acid-fast bacteria in nerves.

Evaluation of monitoring antibodies to PGL-I in armadillos experimentally infected with M. leprae

An enzyme-linked immunosorbent assay (ELISA) for IgM antibodies to the phenolic glycolipid-I antigen of Mycobacterium leprae was evaluated for efficacy in monitoring armadillos experimentally infected with the bacillus. IgM antibodies were detected in armadillos from 186 days after experimental infection until the animals were sacrificed. The ELISA demonstrated the establishment of infection earlier and more reliably than the histologic methods previously applied. Satisfactory yields of M. leprae from individual armadillos could be predicted 97% of the time, and the technique may be useful in identifying appropriate harvest times or resistance among armadillos. The ELISA seems to be a valuable adjunct for managing experimental infections of M. leprae in armadillos.

Evaluation of the origin of Mycobacterium leprae infections in the wild armadillo, Dasypus novemcinctus

An enzyme-linked immunosorbent assay (ELISA) using the phenolic glycolipid-1 (PGL-1) antigen of Mycobacterium leprae and cross-reactive antisera specific for human IgM was developed to detect IgM antibodies to M. leprae in the nine-banded armadillo (Dasypus novemcinctus). Statistical definitions for positive and negative interpretations in the ELISA were developed by screening animals recently captured and experimentally inoculated with M. leprae. The ELISA was shown to have high sensitivity and specificity. Modern day armadillos of central Louisiana were observed to have a PGL-1 antibody prevalence rate as high as 20%, and a clinical disease rate as high as 5%. A retrospective serological survey of 182 armadillos taken in the years 1960-1964 and predating the use of armadillos in leprosy research was used to evaluate the 1968 environmental contamination hypothesis for the origin of M. leprae infections in the wild armadillo. Antibodies to the apparently species-specific PGL-1 antigen were detected in 17 of the samples taken in 1960-1964. Absorption with whole M. leprae, M. intracellulare, M. terrae, M. rhodesiae, M. scrofulaceum, M. diernhoferi, M. kansasii, M. phlei, M. avium, BCG, and 2 new armadillo-derived mycobacterial species showed these antibody reactions to be specific for PGL-1. Apparently, M. leprae was enzootic in armadillos as early as 1961, and original infection of these animals could not have occurred in 1968.

Effect of subcutaneous pox vaccination of young chicks on immune responses and weight gains

Two fowl pox and two pigeon pox vaccines were administered subcutaneously in the dorsum of the neck of specific-pathogen-free (SPAFAS) chicks at day of hatch in separate studies. Treatment levels used were 1:2, 1:10, or 1:50 dilution of the recommended wing web dose. Both pigeon pox vaccines and one fowl pox vaccine depressed body weight gains significantly by day 14. Mean body weight gains of female chicks were less affected by pigeon pox vaccines than by fowl pox vaccines. The mean hemagglutination-inhibition (HI) antibody titer to Newcastle disease virus (NDV) of chicks given one pigeon pox vaccine at the 1:2 dilution was significantly lower (P less than .01) than titers of sham-treated controls. The number of immunoglobulin-M (IgM) secreting cells in the spleen was significantly less (P less than .05) at day 14 in all pox vaccinated chicks when compared to sham-treated controls.

A modified technique for assaying avian immunoglobulin-M-secreting cells

A localized complement-dependent hemolytic assay in modified Cunningham chambers for enumerating avian immunoglobulin-M (IgM)-secreting spleen cells is defined. The maximum number of IgM-secreting spleen cells was present six days after sheep red blood cells (SRBCs) were injected. Intra-abdominal injection of SRBCs resulted in greater but more variable numbers of IgM-secreting cells at the time of maximum response than did either intramuscular or intravenous injection. Fresh chicken serum (FCS) with 10% guinea pig serum was an equally or more effective source of complement for the assay than was FCS alone.