Preventing Maritime Transfer of Toxigenic Vibrio cholerae

Nicole J. Cohen

, Douglas D. Slaten, Nina Marano, Jordan W. Tappero, Michael Wellman, Ryan J. Albert, Vincent R. Hill, David Espey, Thomas Handzel, Ariel Henry, and Robert V. Tauxe

Author affiliations: Centers for Disease Control and Prevention, Atlanta, Georgia, USA (N.J. Cohen, D.D. Slaten, N. Marano, J.W. Tappero, M. Wellman, V.R. Hill, D. Espey, T. Handzel, R.V. Tauxe); US Environmental Protection Agency, Washington, DC, USA (R.J. Albert); and Haitian Ministry of Public Health and Population, Port-au-Prince, Haiti (A. Henry)

Abstract

Organisms, including Vibrio cholerae, can be transferred between harbors in the ballast water of ships. Zones in the Caribbean region where distance from shore and water depth meet International Maritime Organization guidelines for ballast water exchange are extremely limited. Use of ballast water treatment systems could mitigate the risk for organism transfer.

Cholera is an acute diarrheal illness caused by toxigenic strains of the bacterium Vibrio cholerae serogroups O1 and O139. V. cholerae, like other vibrios, is found commonly in marine and estuarine environments, living freely or on surfaces, such as plants and animal shells, and in intestinal contents of marine animals (1). V. cholerae infection is typically acquired by ingestion of contaminated water or food (2).
Ballast water is collected in ships to regulate their stability; the discharge of ballast water can transfer toxigenic V. cholerae O1 from one harbor to another (3). During 1992, shellfish in Mobile Bay, Alabama, on the US coast of the Gulf of Mexico, were contaminated with an epidemic strain of toxigenic V. cholerae O1 from Latin America, although no human illnesses were reported (4). V. cholerae transfer by cargo ship was documented when the same strain was isolated from ballast and other nonpotable water samples collected from 5 cargo ships from ports in Latin America that arrived in the US Gulf of Mexico (5).
To reduce the risk for transfer of invasive species and pathogens between harbors by introduction of contaminated ballast water, the International Maritime Organization (IMO) adopted the International Convention for the Control and Management of Ships’ Ballast Water and Sediments (BWM Convention) on February 13, 2004 (6). Regulation D-2 of the convention establishes numeric ballast water discharge standards, to be phased in with a start date of January 1, 2012, that limit the concentration of viable organisms and human pathogens (including toxigenic V. cholerae, Escherichia coli, and intestinal enterococci). The limit for toxigenic V. cholerae is <1 ballast="ballast" bwm="bwm" cfu="cfu" class="text-underline" conduct="conduct" convention="convention" exchange="exchange" g="g" in="in" interim="interim" ml="ml" or="or" possible="possible" requires="requires" samples.="samples." ships="ships" span="span" that="that" the="the" water="water" weight="weight" wet="wet" whenever="whenever" zooplankton="zooplankton">>
200 nautical miles from the nearest land and in water >200 m deep. If these requirements cannot be met, the exchange should be performed as far from the nearest land as possible, but at a minimum >50 nautical miles from the nearest land and in water >200 m deep. When these requirements cannot be met, areas may be designated where ships can conduct ballast water exchange. Ballast water exchange is based on the principles that 1) organisms from coastal areas will not survive in the open ocean and 2) fewer organisms (including fewer human pathogens) will be taken up in the open ocean, and these will be less likely to adapt to coastal waters. A cholera epidemic emerged in Haiti in October 2010; lack of safe water and sanitation infrastructure and the devastation caused by the January 2010 earthquake contributed to its spread (7). Concerns were raised that cholera could be transferred from Haiti to other countries through contamination of coastal waters by ship ballast water. Ship traffic to Haiti (233 vessel calls in Port-au-Prince in 2008) consists predominantly of cargo vessels with destinations in the United States, other Caribbean islands, and Latin America (8). During an assessment of cholera contamination of fresh and marine water sources in Haiti during the epidemic conducted by the US Centers for Disease Control and Prevention (CDC), US Food and Drug Administration, and the Haitian Ministry of Health and Population, water and seafood collected from harbors at Port-au-Prince and St. Marc were tested for viable V. cholerae and for the cholera toxin gene (ctxA) (9). Toxigenic V. cholerae O1 serotype Ogawa indistinguishable from the outbreak strain was isolated from seafood samples from Port-au-Prince. Although V. cholerae was not isolated from marine water samples, the ctxA gene was detected in broth cultures of seawater samples from both harbors, suggesting that harbor waters were contaminated with toxigenic V. cholerae.