Monday, June 8, 2009

Cholera and spirochetes: Introducing Brachyspira!

ResearchBlogging.orgCholera results in a severe form of diarrhea that can lead to dehydration, shock, and ultimately death without prompt treatment. The disease afflicts the poor in developing countries lacking clean water sources and sanitation infrastructure. Vibrio cholerae is the causative agent and can be viewed by microscopic examination of the so-called "rice-water" stool samples from cholera patients.

rice-water stool from a cholera patient (Figure 1 from Sack et al., 2004)

As reported in a recent issue of Emerging Infectious Diseases, Nelson and colleagues, while examining a cholera outbreak in Bangladesh back in 2006, found that stool samples in over a third of cholera patients contained spirochetes mingling with V. cholerae. Samples were fluorescently stained to aid identification of bacteria. One example is shown below. V. cholerae were visualized with a FITC-conjugated monoclonal antibody to its lipopolysaccharide (in red), and bacterial DNA was stained wtih DAP I (green). Only the merged image is shown below. V. cholerae are the rods with a slight bend and appear yellow (combination of red and green) with a red edge; the spirochetes are the W-shaped forms stained green.

bar = 10 ┬Ám

This wasn't the first time spirochetes were observed in rice-water stool. Over a century ago, Theodor Escherich (the discoverer of E. coli) was the first to witness spiral-shaped microbes in fecal samples from cholera victims.

What was the identity of these spirochetes? They were not any of the "Big 3" of Borrelia, Treponema, and Leptospira, which garner the most attention from spirochete researchers (and from the writer of this blog). Nelson and colleagues guessed that they were members of the genus Brachyspira as they are the only spirochetes known to live in the human intestine. They turned out to be correct. They successfully amplified the gene encoding the 16s rRNA with Brachyspira-specific PCR primers. The sequence of the PCR product revealed the spirochetes to be Brachyspira pilosicoli and Brachyspira aalborgi.

Brachyspira account for most cases of human intestinal spirochetosis, defined as the presence of spirochetes in the colon. Although colonization of the large intestine by spirochetes is uncommon in the Western world, up to half of those in developing nations may harbor intestinal spirochetes. A typical example is shown below (click on image for larger version).

Figure 3 from Esteve et al., 2006

The sectioned tissue, which was stained with H&E, was obtained by colonic biopsy. The left panel reveals a fuzzy layer covering the colonic epithelium. These are Brachyspira attached at one end to the lining of the colon. The density of spirochetes can reach up to 1,700 per square millimeter. The right panel shows a colonic biopsy from the same patient after successful treatment with the antimicrobial agent metronidazole. Note that the fuzzy layer has disappeared.

Whether intestinal spirochetes cause disease in humans is unclear. Many people with intestinal spirochetes do not suffer any ill effects, but others endure chronic diarrhea. The mode of transmission of Brachyspira is unknown, but scientists have surmised that ingestion of contaminated water is involved.

The role of Brachyspira in cholera, if any, is even more of a mystery. In the conclusion to their article, Nelson et al. present the hypothesis that intestinal spirochetes exacerbate the already devastating clinical course of cholera.

Featured paper

Nelson, E.J., Tanudra, A., Chowdhury, A., Kane, A.V., Qadri, F., Calderwood, S.B., Coburn, J., Camilli, A. (2009). High Prevalence of Spirochetosis in Cholera Patients, Bangladesh Emerging Infectious Diseases, 15 (4), 571-573 DOI: 10.3201/eid1504.081214

Other references

Esteve, M., Salas, A., Fernandez-Banares, F., Lloreta, J., Marine, M., Gonzalez, C.I., Forne, M., Casalots, J., Santaolalla, R., Espinos, J.C., Munshi, M.A., Hampson, D.J., and Viver, J.M. (2006). Intestinal spirochetosis and chronic watery diarrhea: Clinical and histological response to treatment and long-term follow up. Journal of Gastroenterology and Hepatology 21(8):1326-1333. DOI: 10.1111/j.1440-1746.2006.04150.x

Sack, D.A., Sack, R.B., Nair, G.B., and Siddique, A.K. (2004). Cholera. Lancet 363(9404):223-233. DOI: 10.1016/S0140-6736(03)15328-7