Brachyspira pilosicoli

Lore & Background

Although spirochetes were described as early as 1877, Brachyspira pilosicoli was first described in 1980 when isolates from pigs with diarrhea were found to differ from Brachyspira hyodysenteriae in morphology and pathology. It was later attributed as the agent of 'intestinal spirochetosis,' a name reflecting the microscopic appearance of spirochetes coating enterocytes like a brush border, though Dr. Claude O. Burdick disputed this, suggesting the appearance was due to tangential sectioning of normal microvilli. Following these early descriptions, the bacterium was discovered in various human populations, including Asian communities, homosexual communities, and communities in Muscat, Oman, as well as in chickens, where it caused production losses. It was not until the mid-1990s that the pathogen was unified under the species name Brachyspira pilosicoli across pigs, chickens, and humans.

Reader's Guide

Brachyspira pilosicoli is significant as a pathogen that affects both animal agriculture and human public health. In pigs, it causes porcine intestinal spirochetosis, characterized by diarrhea with a 'wet cement' appearance, reduced productivity, and economic losses, especially during weaning and mixing. In poultry, it causes avian intestinal spirochetosis, primarily in laying hens and breeding flocks, leading to decreased egg production, delayed onset of lay, and increased mortality. In humans, infection is uncommon but associated with colonic spirochetosis, with highest prevalence in developing countries and conditions of poverty. The bacterium's ability to colonize multiple host species—including pigs, chickens, dogs, wild birds, rodents, and humans—makes it a unique and important pathogen. Its resilience, such as tolerance to direct oxygen exposure despite being anaerobic, and its difficult culture on media, requiring genetic sequencing for accurate identification, add to the challenges of studying and controlling it. The variability in disease severity, from subclinical to severe, and the role of diet and spirochete burden in pathogenesis, underscore the complexity of infections. The bacterium's lipooligosaccharide cell wall and flagella are implicated in virulence, though specific adhesins and toxins have not been identified.

Did You Know?

• Brachyspira pilosicoli was first described in 1980 from pigs with diarrhea, distinguishing it from Brachyspira hyodysenteriae.
• It creates a 'false brush border' by attaching end-on to colonic enterocytes, a feature disputed by Dr. Claude O. Burdick as possibly being normal microvilli sectioned tangentially.
• The bacterium is difficult to grow in culture, taking at least 3 days on trypticase soy blood agar, and species-level identification requires genetic sequencing like PCR.
• Brachyspira pilosicoli colonizes a wide range of hosts including pigs, chickens, dogs, wild birds, rodents, and humans, making it unique among Brachyspira species.