Emerging Tuberculosis Pathogen Hijacks Social Communication Behavior in the Group-Living Banded Mongoose (Mungos mungo)

Abstract

An emerging Mycobacterium tuberculosis complex (MTC) pathogen, M. mungi, infects wild banded mongooses (Mungos mungo) in Northern Botswana, causing significant mortality. This MTC pathogen did not appear to be transmitted through a primary aerosol or oral route. We utilized histopathology, spoligotyping, mycobacterial interspersed repetitive units-variable number of tandem repeats (MIRU-VNTR), quantitative PCR (qPCR), and molecular markers (regions of difference [RDs] from various MTC members, including region of difference 1 [RD1] from M. bovis BCG [RD1(BCG)], M. microti [RD1(mic)], and M. pinnipedii [RD1(seal)], genes Rv1510 [RD4], Rv1970 [RD7], Rv3877/8 [RD1], and Rv3120 [RD12], insertion element IS1561, the 16S RNA gene, and gene Rv0577 [cfp32]), including the newly characterized mongoose-specific deletion in RD1 (RD1(mon)), in order to demonstrate the presence of M. mungi DNA in infected mongooses and investigate pathogen invasion and exposure mechanisms. M. mungi DNA was identified in 29% of nasal planum samples (n = 52), 56% of nasal rinses and swabs (n = 9), 53% of oral swabs (n = 19), 22% of urine samples (n = 23), 33% of anal gland tissue (n = 18), and 39% of anal gland secretions (n = 44). The occurrence of extremely low cycle threshold values obtained with qPCR in anal gland and nasal planum samples indicates that high levels of M. mungi can be found in these tissue types. Histological data were consistent with these results, suggesting that pathogen invasion occurs through breaks in the nasal planum and/or skin of the mongoose host, which are in frequent contact with anal gland secretions and urine during olfactory communication behavior. Lesions in the lung, when present, occurred only with disseminated disease. No environmental sources of M. mungi DNA could be found. We report primary environmental transmission of an MTC pathogen that occurs in association with social communication behavior.

Importance: Organisms causing infectious disease evolve modes of transmission that exploit environmental and host conditions favoring pathogen spread and persistence. We report a novel mode of environmental infectious disease transmission that occurs in association with olfactory secretions (e.g., urine and anal gland secretions), allowing pathogen exposure to occur within and between social groups through intricate social communication behaviors of the banded mongoose host. The presence of M. mungi in these environmentally deposited secretions would effectively circumvent natural social barriers (e.g., territoriality), facilitating between-group pathogen transmission in the absence of direct physical contact, a rare occurrence in this highly territorial species. This work identifies an important potential mechanism of pathogen transmission of epidemiological significance in social species. We also provide evidence of a novel mechanism of pathogen transmission for the MTC complex, where pathogen movement in the environment and host exposure dynamics are driven by social behavior.

FIG 1

Nasal turbinate from Mycobacterium mungi-infected banded mongoose. (A) Submucosa (SM) is markedly expanded by infiltrates of macrophages, with abundant foamy eosinophilic cytoplasm. Lesser numbers of lymphocytes are also present. Expanded submucosa is covered by intact, ciliated nasal mucosal epithelium (between arrows) (HE staining; magnification, ×10). (B) Submucosa contains numerous magenta acid-fast bacilli. (C) Cartilage (Zeihl-Neelsen staining; magnification, ×40).

FIG 2

Mycobacterium mungi invasion occurs through injuries to the nasal planum and/or skin of banded mongooses. (A) Healthy adult mongooses. (B) Adult mongooses with advanced tuberculosis disease: tuberculosis lesions are found in the hairless parts of the mongoose nose (nasal planum and cavity), with granulomatous inflammation, erosion, and ulcerations, as well as distortion of the nasal cavity. M. mungi also appears to invade the mongoose host through skin lesions, often sites of previous injury. Pulmonary infection has only been detected in advanced (e.g., disseminated) disease.

FIG 3

Skin sample from Mycobacterium mungi-infected banded mongoose. Note magenta acid-fast bacilli in debris and desquamated epithelial cells on the surface of intact epidermis. Zeihl-Neelsen staining; magnification, ×40.

FIG 4

Lung tissue from Mycobacterium mungi-infected banded mongoose. Lung lesions are characterized by multifocal granulomas oriented around vasculature (long arrows) rather than airways (asterisk). Subpleural lesions expand the subpleural space and extend into the parenchyma (short arrows). HE staining; magnification, ×10.

FIG 5

Spoligotype analysis of the emerging pathogen Mycobacterium mungi and representative M. tuberculosis complex organisms. The unique spoligotype of M. mungi (672600000000671) is identified in tissues of infected banded mongooses BM10109 and BM9209; MTC typing panel results are also shown in Fig. 6, and external lesions of M. mungi infection in mongoose BM10109 are shown in Fig. 2 (bottom right, see facial and leg lesions). Clinical diagnostic cases are included for comparison: the M. bovis isolate (264073777777600) was recovered from a cow, and the M. tuberculosis isolate (777777777760751) from a nonhuman primate. Strains H36Rv and BCG are used as controls.

FIG 6

Mycobacterium mungi evaluation with an M. tuberculosis complex (MTC) typing panel. M. mungi can be distinguished from other MTC organisms by the presence or absence of PCR amplicons. M. mungi and M. africanum present with a similar pattern on this panel, as would the other lineage 6 members, dassie bacillus and M. suricattae. However, M. mungi can be differentiated from these MTC members by the presence of a unique deletion in region of difference 1 (RD1^mon; see Table 2).

FIG 7

Schematic of region of difference 1 (RD1) in Mycobacterium mungi and other organisms.

FIG 8

Environmental sampling sites in the home range of infected banded mongooses. The study site is within the black box on the map of Botswana (inset).

FIG 9

Mycobacterium mungi can infect the banded mongoose host through anal gland secretions and urine used in social communication behavior. (A) Banded mongooses can be injured through behavioral interactions with conspecifics, other vertebrate and invertebrate organisms, as well as injuries from the physical environment. (B) Contact with infected anal gland secretions through communication behavior allows the pathogen to invade the mongoose host through these injuries and pathogen transmission to occur between and within social groups, overcoming social barriers to transmission. (C) Pathogen invasion results in tuberculosis disease that causes high levels of mortality among banded mongooses, threatening smaller groups with extirpation (second and third photographs, mongoose BM10109; see Fig. 5 for spoligotype results and Fig. 6 for MTC typing panel results).

FIG 10

Range overlap for known reservoir hosts of lineage 6 Mycobacterium tuberculosis complex (MTC) organisms most closely related to M. mungi. The only known populations of M. mungi-infected banded mongoose occur in Northern Botswana and northwest Zimbabwe. The banded mongoose range distribution overlaps areas with other MTC lineage 6 reservoir hosts—the rock hyrax, Procavia capensis (dassie bacillus), and meerkat, Suricata suricatta (Mycobacterium suricattae). In areas where M. mungi-infected populations of banded mongoose have been identified (dashed line), no range overlap with these species or any other known wildlife or domestic animal reservoirs of tuberculosis occurs. Distribution data were obtained from references to 60).