Vibrio cholerae is unusual in that it competes in the natural environmental community of bacteria in estuarine and brackish waters worldwide. V. cholerae bacteria can increase their numbers in the environment by successfully infecting humans. For a person to be infected by cholera, the bacteria’s genetic material must be present in the intestine. One person infected with cholera can shed into the environment a one-million fold increase in V. cholerae numbers through a single episode of diarrhea. Below are some highlights of recent cholera research by NIAID-supported investigators.
Evolution on the Crab Shell
A research team led by NIAID grantee Gary Schoolnik, Ph.D., of Stanford University in Palo Alto, California, showed how well V. cholerae could evolve and persist in the environment. Cholera bacteria colonizing chitin surfaces, like those present on aquatic crustaceans, were able to exchange complete sets of the DNA that determined the virulence of the bacteria.
- Meibom KL, Blokesch M, Dolganov NA, Wu CY, Schoolnik GK. Chitin induces natural competence in Vibrio cholerae. Science. 310(5755):1824-7 (2005).
- Blokesch M, Schoolnik GK. Serogroup conversion of Vibrio cholerae in aquatic reservoirs. PLoS Pathogens. 3(6):e81 (2007).
Cholera Emergence in Haiti
Following a devastating earthquake in January 2010, Haiti experienced a confirmed cholera outbreak later in the year. Bioinformatic analysis revealed that the five Haitian cholera isolates sequenced to date are very closely related to one another, supporting a theory that cholera arrived in Haiti from a single source. Genetic comparisons with 23 other sequenced cholera strains showed that the strains in Haiti were more closely related to strains from South Asia than to strains from East Africa or Latin America. The genetic analysis also found that Haitian strains had the genetic features of novel variant cholera strains that cause increased virulence, drug resistance, and possibly more robust environmental persistence. The authors warned that the Haitian isolate presents a renewed threat of cholera to the Western hemisphere. They recommended that healthcare professionals consider public health measures including vaccination to control cholera in Haiti and counter its spread.
- Chin CS, Sorenson J, Harris JB, Robins WP, Charles RC, Jean-Charles RR, Bullard J, Webster DR, Kasarskis A, Peluso P, Paxinos EE, Yamaichi Y, Calderwood SB, Mekalanos JJ, Schadt EE, Waldor MK. The origin of the Haitian cholera outbreak strain. New Engl J Med. 364(1):33-42 (2011). Epub 2010 Dec 9.
Improved sanitation would greatly aid cholera prevention, but populations throughout the world lacking safe water increase every year due to poverty, insufficient housing, and flooding from atmospheric or oceanic extremes.