The Spirochete Brachyspira pilosicoli, Enteric Pathogen of Animals and Humans

Abstract

SUMMARY Brachyspira pilosicoli is a slow-growing anaerobic spirochete that colonizes the large intestine. Colonization occurs commonly in pigs and adult chickens, causing colitis/typhlitis, diarrhea, poor growth rates, and reduced production. Colonization of humans also is common in some populations (individuals living in village and peri-urban settings in developing countries, recent immigrants from developing countries, homosexual males, and HIV-positive patients), but the spirochete rarely is investigated as a potential human enteric pathogen. In part this is due to its slow growth and specialized growth requirements, meaning that it is not detectable in human fecal samples using routine diagnostic methods. Nevertheless, it has been identified histologically attached to the colon and rectum in patients with conditions such as chronic diarrhea, rectal bleeding, and/or nonspecific abdominal discomfort, and one survey of Australian Aboriginal children showed that colonization was significantly associated with failure to thrive. B. pilosicoli has been detected in the bloodstream of elderly patients or individuals with chronic conditions such as alcoholism and malignancies. This review describes the spirochete and associated diseases. It aims to encourage clinicians and clinical microbiologists to consider B. pilosicoli in their differential diagnoses and to develop and use appropriate diagnostic protocols to identify the spirochete in clinical specimens.

Severe Human Intestinal Spirochetosis: An Unusual Cause of Diffuse Colonic Ulcerations in a Patient Living With HIV

“…B. pilosicoli surface lipoproteins may be involved in facilitating this attachment by undergoing protein-protein interactions with speci c receptors on the cell surface. e appearance of a "false brush border" is shown if a su cient number of cells become attached and where massive colonization occurs, it may cause a physical impedance to water and electrolyte absorption through the colonic enterocytes and hence contribute to diarrhea [5].…”

Hiding in Plain Sight: Colonic Spirochetosis in Humans

“…Currently, nine Brachyspira species are recognized (B. aalborgi, B. alvinipulli, B. hampsonii, B. hyodysenteriae, B. innocens, B. intermedia, B. murdochii, B. pilosicoli, and B. suanatina), but to date only B. aalborgi and B. pilosicoli are known to colonize humans. While the natural host ranges of these organisms have not been studied thoroughly, B. aalborgi is reported to colonize humans, nonhuman primates, and opossums, whereas B. pilosicoli has been found in humans, swine, dogs, and birds (5,6). A new species, "B. catarrhinii," has been proposed; it encompasses a group of organisms (previously characterized as subset of B. aalborgi) that colonize monkeys (7).…”

“…However, Walker et al (18) noted that the occurrence of clusters of eosinophils in the subepithelial tissue of the colon was significantly associated with HCS. Additionally, clearance of HCS spontaneously or through treatment with metronidazole or other antimicrobial agents may result in resolution of symptoms in chronic diarrhea in some cases (6,16,19). Perhaps the occurrence of gastrointestinal symptoms may result from the combination of HCS and as yet undefined host factors.…”

“…Should a more extensive, blinded, and controlled inoculation study in humans be performed, as has been done with norovirus and other human gastrointestinal pathogens? How is HCS transmitted: through direct human-tohuman contact, through animal-to-human transmission (in the case of B. pilosicoli), via contaminated water or food supplies (6,23,24), or by other means? Do humans vary in susceptibility to colonization or disease manifestations, and to what extent is this aspect related to genetic factors, immune status, hygiene, overall health, sexual activity, socioeconomic influences, climate, and additional parameters?…”

Isolates from colonic spirochaetosis in humans show high genomic divergence and carry potential pathogenic features but are not detected by 16S amplicon sequencing using standard primers for the human microbiota

“…The nucleotide sequences were aligned using muscle and a phylogenetic tree was 7 reconstructed using PhyML as described above. 8 9 To study the genetic variability between the CS strains and hitherto described genomes 10 within the Brachyspira genus listed in Table S1, an average nucleotide identity (ANI) analysis 11 was performed using MUMmer alignment 32 implemented in the pyani software v. 0.2.7 12 (https://github.com/widdowquinn/pyani). 13 B. sp.…”